Immune System

Primary immunodeficiency in adults: when to suspect and workup

Clinical Overview and When to Suspect Primary Immunodeficiency in Adults

— ≥2 pneumonias in 1 year, or ≥4 sinopulmonary infections/year

— Need for IV antibiotics to clear infection

— Recurrent deep-tissue or organ abscesses

— Persistent thrush or invasive fungal infection

— Infection with opportunistic or unusual pathogens (PJP, disseminated NTM, chronic norovirus, JC virus)

— Family history of PID or unexplained early death

— Bronchiectasis without obvious cause (CF, smoking)

— Recurrent severe encapsulated organism infection (S. pneumoniae, H. influenzae, N. meningitidis)

— Granulomatous disease mimicking sarcoidosis (CVID)

— Autoimmune cytopenias, especially ITP + AIHA = Evans syndrome in CVID

— Unexplained lymphoproliferation or splenomegaly

— GI: chronic diarrhea, nodular lymphoid hyperplasia, sprue-like enteropathy

— Early-onset lymphoma in a young adult

Board pearl: Think PID in any adult with bronchiectasis + recurrent sinopulmonary infections + low immunoglobulins — the answer is CVID until proven otherwise. Step 3 management: First move is quantitative immunoglobulins (IgG, IgA, IgM) plus HIV testing — don't jump to genetic panels.

Primary immunodeficiency (PID) is increasingly recognized in adults — median diagnostic delay is 6–9 years from symptom onset, and roughly 25–40% of patients with PID are diagnosed after age 18.

Adult-onset PID is predominantly humoral (antibody deficiency): common variable immunodeficiency (CVID), selective IgA deficiency, specific antibody deficiency, IgG subclass deficiency.

Less common but high-yield in adults: complement deficiencies (recurrent Neisseria), C1-esterase inhibitor deficiency (hereditary angioedema), late-presenting combined immunodeficiency, CTLA-4 haploinsufficiency, NF-κB pathway defects.

Jeffrey Modell Foundation "10 warning signs" — adult-adapted red flags:

Non-infectious clues that PID is hiding underneath:

Presentation Patterns and Key History

— Severe infections (sepsis, meningitis, empyema)

— Persistent infections (chronic sinusitis, thrush failing fluconazole)

— Unusual organisms or Unusual sites (PJP in non-HIV, disseminated MAC, brain abscess from Aspergillus)

— Recurrent infections (≥2 pneumonias, ≥4 sinusitis/otitis episodes per year)

— Encapsulated bacteria (pneumococcus, Hib, meningococcus) → humoral or complement

— Recurrent Neisseria (meningitis or gonococcemia) → terminal complement C5–C9 or properdin

— PJP, CMV, disseminated fungal, chronic cryptosporidium → T-cell or combined

— Staphylococcal skin/liver abscesses, Aspergillus, Serratia, Burkholderia → chronic granulomatous disease (phagocyte)

— Disseminated NTM or salmonella → IFN-γ/IL-12 axis defect

— Recurrent HSV/VZV severe disease → NK-cell or TLR3 defects

— Autoimmune disease (ITP, AIHA, thyroiditis, vitiligo, IBD-like enteritis)

— Atopic and allergic history (hyper-IgE thinking)

— Family deaths from infection or lymphoma; consanguinity

— Transfusion history (need irradiated products if T-cell defect suspected)

— Live vaccine reactions (BCG-itis suggests T-cell defect)

— Medications: rituximab, chronic steroids, anti-seizure drugs, mycophenolate — cause secondary hypogammaglobulinemia (must exclude)

— Protein loss: nephrotic syndrome, protein-losing enteropathy

Key distinction: Adult CVID typically presents 20s–40s with sinopulmonary infections plus autoimmunity or GI disease; selective IgA deficiency is usually asymptomatic but flags risk of anaphylaxis to blood products containing IgA. Board pearl: Always ask about rituximab in the past 12 months before calling new hypogammaglobulinemia "primary."

Step 3 stems frequently disguise PID as "recurrent sinusitis" or "third pneumonia this year" in a 25–45-year-old. Pattern recognition saves the question.

Infection-pattern history — the SPUR mnemonic:

Pathogen-to-defect mapping (high yield):

Non-infectious history to elicit:

Physical Exam Findings and Bedside Assessment

— Chronic rhinorrhea, nasal polyps, septal perforation

— Tympanic membrane scarring, conductive hearing loss from recurrent otitis

— Oral thrush, angular cheilitis, severe periodontitis (think LAD, hyper-IgE, neutrophil defects)

— Absent tonsils/adenoids in young adult → X-linked agammaglobulinemia (Bruton) clue

— Coarse crackles, clubbing, hyperinflation

— Bronchiectasis sequelae — productive cough, hemoptysis

— Splenomegaly (CVID, ALPS, granulomatous disease)

— Diffuse adenopathy — granulomatous-lymphocytic interstitial lung disease (GLILD) often coexists

— Absent lymphoid tissue → agammaglobulinemia

— Eczema + cold abscesses + coarse facies + retained primary teeth → Hyper-IgE (Job) syndrome

— Oculocutaneous albinism + recurrent infections → Chédiak-Higashi

— Telangiectasias on conjunctiva/ears + ataxia → Ataxia-telangiectasia

— Petechiae + eczema in a male → Wiskott-Aldrich (rare in adults but tested)

— Non-healing umbilical stump history, delayed wound healing → LAD

— Recurrent painless, non-pitting angioedema without urticaria → HAE (C1-INH deficiency)

CCS pearl: On a CCS case, after history pointing to PID, order vitals, pulse ox, CBC with differential, CMP, quantitative immunoglobulins, HIV, CXR as your opening move — this batch reliably advances the case. Board pearl: Absent tonsils in an adult male with recurrent encapsulated infections = XLA presenting late.

PID exam is a systems sweep looking for chronic infection sequelae, lymphoid abnormalities, and syndromic clues.

HEENT:

Pulmonary:

Lymphoreticular:

Skin (high yield for syndromic PID):

GI/Hepatic: hepatosplenomegaly, chronic diarrhea, weight loss; nodular lymphoid hyperplasia on prior endoscopy.

Neuro: chronic enteroviral meningoencephalitis (XLA), cerebellar ataxia (A-T).

Vitals/hemodynamics: during acute infection, assess for sepsis (qSOFA, lactate); chronic disease patients may decompensate quickly because of poor reserve.

Diagnostic Workup — Initial Labs, Imaging, and Biomarkers

— CBC with differential — lymphopenia (<1000) is abnormal in adults and demands a cause; neutropenia or eosinophilia clues

— Comprehensive metabolic panel — albumin (rule out protein loss), LFTs

— Quantitative immunoglobulins: IgG, IgA, IgM, IgE

— HIV 4th-generation Ag/Ab — mandatory before labeling primary

— Urinalysis — proteinuria suggests nephrotic loss

— HIV-negative + low IgG/IgA ± low IgM is the gateway to humoral PID workup

— Specific antibody titers to prior vaccines: tetanus, diphtheria, pneumococcal (23-valent polysaccharide), H. influenzae

— If low → immunize with Pneumovax-23 and recheck titers in 4–6 weeks; failure to mount a 2-fold rise to ≥70% of serotypes = specific antibody deficiency

— IgG subclasses (IgG1–4) — interpret cautiously; isolated subclass deficiency rarely clinically meaningful without functional defect

— High-resolution chest CT if recurrent pneumonia or chronic cough — defines bronchiectasis distribution, GLILD, lymphadenopathy

— Sinus CT for chronic sinusitis evaluation

— Abdominal imaging if splenomegaly or lymphoma suspicion

— β2-microglobulin, LDH if lymphoproliferation

— C3, C4, CH50 screen complement; AH50 screens alternative pathway

— C4 low + recurrent angioedema → C1-INH level and function (HAE)

— Flow cytometry for lymphocyte subsets (CD3, CD4, CD8, CD19, CD56) — quantitates T, B, NK cells

— Tryptase, IgE if hyper-IgE suspected

Step 3 management: When IgG is low, always confirm it's not secondary — check albumin, urine protein, medication list (rituximab, anti-epileptics, MMF, chronic steroids), and exclude multiple myeloma with SPEP/UPEP and free light chains in older adults. Board pearl: Low IgG + monoclonal spike + recurrent infection in a 60-year-old = multiple myeloma, not CVID.

Tier 1 screen — order on every suspected adult PID:

Tier 2 — humoral function (the actual test of B-cell competence):

Imaging:

Biomarkers and adjuncts:

Diagnostic Workup — Advanced and Confirmatory Studies

— CVID diagnostic criteria (ESID): age ≥4, marked decrease in IgG + low IgA and/or IgM, poor vaccine response, exclusion of secondary causes, symptoms ≥4 years (recent update allows shorter if criteria clear)

— XLA: male, CD19+ B cells <2%, absent or very low all immunoglobulin classes, BTK gene mutation

— Hyper-IgM syndrome: low IgG/IgA, normal or elevated IgM; CD40L flow cytometry (X-linked) or AID/UNG sequencing

— Selective IgA deficiency: IgA <7 mg/dL with normal IgG and IgM

— Lymphocyte subset flow cytometry with CD4/CD8 ratio

— Mitogen and antigen proliferation assays (PHA, ConA, candida, tetanus)

— DHR (dihydrorhodamine) flow assay — gold standard for chronic granulomatous disease; replaced NBT in most centers

— NK-cell function if recurrent herpesvirus disease

— Low CH50 + normal AH50 → classical pathway defect (C1, C2, C4)

— Low AH50 + normal CH50 → alternative pathway (factor B, properdin)

— Both low → C3 or terminal (C5–C9) deficiency — terminal = recurrent Neisseria

— Order targeted gene panels when phenotype is suggestive (NGS PID panels of 200–400 genes)

— Whole-exome sequencing for atypical or syndromic presentations

— Counseling and informed consent for incidental findings; coordinate with clinical immunology and genetics

— Lung biopsy for GLILD vs lymphoma vs infection

— GI biopsy for sprue-like enteropathy (no plasma cells in CVID enteritis)

— Bone marrow if cytopenias or to exclude lymphoma/myeloma

Key distinction: Failure of vaccine response (not just low IgG) is what makes the diagnosis of antibody deficiency — a normal IgG with poor specific titers can still mean specific antibody deficiency. Board pearl: Recurrent Neisseria meningitidis = check CH50/AH50 and treat presumptively as terminal complement deficiency.

When Tier 1–2 confirm humoral deficiency, classify the defect:

T-cell evaluation when indicated (opportunistic infections, lymphopenia):

Complement workup:

Genetic testing — Step 3 framework:

Tissue/procedure-based:

Risk Stratification and First-Line Management Logic

— High risk / urgent IVIG initiation: IgG <300–400 mg/dL with active infection, bronchiectasis, or sepsis history; combined immunodeficiency phenotype; ongoing organ damage

— Moderate risk: Recurrent infections with IgG 400–600 and poor vaccine response — start replacement after confirming functional defect

— Surveillance only: Selective IgA deficiency or isolated IgG subclass deficiency without infections — counsel, vaccinate, no replacement

— Documented antibody deficiency (low IgG and failed vaccine response) plus clinical infections or end-organ damage → YES

— Asymptomatic isolated lab abnormality → generally no

— Baseline IgG trough, IgA (anti-IgA antibodies risk anaphylaxis in IgA-deficient patients), renal function, LFTs

— Hepatitis B/C, HIV serology — establishes pre-replacement status

— Pneumococcal, Hib, tetanus titers (post-replacement they'll reflect donor pool, not patient)

— Vaccination catch-up before starting replacement when possible

— Lower threshold for cultures and antibiotics

— Cover encapsulated organisms empirically (amoxicillin-clavulanate, ceftriaxone) for sinopulmonary

— Avoid live vaccines once combined or T-cell defect suspected

— Clinical immunology, pulmonology (bronchiectasis), GI (enteropathy), hematology (cytopenias/lymphoma)

— Genetic counseling for inherited forms

— Insurance pre-authorization for IVIG/SCIG — a real Step 3 systems issue

Step 3 management: Don't start IVIG on isolated low IgG — document infections + failed vaccine response first. This protects the patient from lifelong therapy they don't need and is explicitly the guideline-driven approach. CCS pearl: Order baseline IgA and hepatitis serologies before the first IVIG dose; the case will penalize you for missing them.

Severity triage of the newly diagnosed adult PID patient:

Decision framework — does this patient need immunoglobulin replacement?

Pre-treatment baseline (must obtain before first IVIG dose):

Acute infection management runs in parallel:

Multidisciplinary coordination:

Pharmacotherapy — First-Line Regimen

— Dose: 400–600 mg/kg every 3–4 weeks, titrate to IgG trough ≥700–800 mg/kg (higher, 800–1000, if bronchiectasis present)

— Premedicate with acetaminophen + diphenhydramine ± hydrocortisone for infusion reactions

— Slow initial rate; monitor for headache, aseptic meningitis, thromboembolism, hemolysis, AKI

— Hydration before infusion reduces renal and thrombotic risk

— 100–200 mg/kg weekly (or biweekly), self-administered at home

— Steadier serum levels, fewer systemic reactions, less wear-off fatigue

— Local site reactions common but mild; ideal for needle-tolerant motivated patients

— Facilitated SCIG (with hyaluronidase) allows monthly dosing

— IVIG: poor venous access fine if port available; monthly clinic visit; useful when high doses needed acutely

— SCIG: better quality of life, fewer systemic reactions, preferred in patients with prior IVIG reactions, renal disease, thrombotic risk, or anti-IgA antibodies

— Azithromycin 250–500 mg 3×/week or daily TMP-SMX or amoxicillin

— Particularly valuable in bronchiectasis with frequent exacerbations

— Inactivated vaccines (influenza, pneumococcal PCV20 or PCV15→PPSV23, Tdap) — still give, though response may be blunted; titers won't be interpretable once on IVIG

— Avoid live vaccines (MMR, varicella, yellow fever, live zoster, nasal flu, BCG) in CVID, XLA, combined defects

— Recombinant zoster (Shingrix) is safe and recommended

— HAE: C1-INH concentrate, ecallantide, icatibant for acute attacks; lanadelumab/berotralstat for prophylaxis

— CGD: lifelong itraconazole + TMP-SMX + IFN-γ

— IPEX, CTLA-4 haploinsufficiency: abatacept, sirolimus

Board pearl: Target IgG trough ≥800 mg/dL in patients with bronchiectasis — higher troughs reduce exacerbations. Step 3 management: A patient on IVIG with sudden flank pain and rising creatinine = IVIG-induced AKI from sucrose-stabilized product or osmotic injury — switch product, hydrate, hold dose.

Immunoglobulin replacement is the cornerstone of antibody-deficiency therapy.

IVIG (intravenous):

SCIG (subcutaneous):

Choosing IVIG vs SCIG:

Antibiotic prophylaxis (adjunct or alternative when replacement insufficient):

Vaccination strategy:

Targeted therapies for specific PIDs:

Expanded Pharmacology and Special Therapeutics

— Headache and aseptic meningitis: slow rate, switch products, pretreat with NSAIDs; high-dose IVIG users at most risk

— Thromboembolism: higher risk in elderly, obese, immobile, prior VTE — choose lower-osmolality, IgA-poor products, hydrate, slower rate

— Hemolysis: anti-A/anti-B isohemagglutinins in IVIG; monitor H/H, especially in non-O blood types

— Anaphylaxis with anti-IgA antibodies: use IgA-depleted products (e.g., specific brands); pretest in IgA-deficient patients with infection history

— Renal injury: avoid sucrose-containing products; ensure hydration; reduce rate

— Lanadelumab (anti-kallikrein mAb) SC every 2–4 weeks — first-line long-term prophylaxis

— Berotralstat oral kallikrein inhibitor daily

— C1-INH concentrate IV twice weekly

— Androgens (danazol) — older, hepatotoxic, contraindicated in pregnancy

— Acute attack: icatibant (bradykinin B2 antagonist) SC, ecallantide SC, or C1-INH IV — NOT epinephrine, antihistamines, or steroids (mechanism is bradykinin, not histamine)

— Curative for severe combined immunodeficiency, CGD, hyper-IgM, Wiskott-Aldrich, some CVID-like monogenic disorders (CTLA-4, LRBA)

— Adult HSCT increasingly viable with reduced-intensity conditioning

— Referral to specialty center; assess organ damage, donor availability

— Approved/emerging for ADA-SCID, X-SCID, WAS, CGD — usually pediatric but adult eligibility expanding

— Sirolimus for ALPS, CTLA-4 haploinsufficiency

— Abatacept for CTLA-4 deficiency, LRBA deficiency

— Ruxolitinib for STAT1 gain-of-function

Key distinction: HAE angioedema does not respond to epinephrine, antihistamines, or steroids — if a patient has recurrent angioedema unresponsive to these, the answer is C1-INH testing and bradykinin-pathway therapy. Board pearl: IVIG-related hemolysis is more common in non-O blood groups and after high-dose therapy (e.g., for ITP).

Managing IVIG/SCIG adverse effects:

Pharmacology of HAE prophylaxis (Step 3 favorite):

Hematopoietic stem cell transplant (HSCT):

Gene therapy:

Targeted small molecules for immune dysregulation:

Special Populations — Elderly and Renal/Hepatic Impairment

— Adults presenting in their 60s–70s with hypogammaglobulinemia must have myeloma, CLL, lymphoma, and thymoma (Good syndrome) excluded

— Good syndrome: thymoma + hypogammaglobulinemia + recurrent infections + diarrhea ± pure red cell aplasia — get chest CT in any older adult with new hypogammaglobulinemia

— Drug-induced hypogammaglobulinemia is common: rituximab, MMF, anti-epileptics (phenytoin, carbamazepine), chronic corticosteroids — review meds

— IVIG carries risk of osmotic nephrosis and AKI, especially with sucrose-stabilized products

— Use non-sucrose, low-osmolality IVIG (10% liquid preparations) in CKD

— Reduce infusion rate; ensure euvolemia; monitor creatinine pre- and post-infusion

— SCIG is renal-safer — preferred in CKD stage ≥3

— Adjust antimicrobial prophylaxis: TMP-SMX raises creatinine and K+; azithromycin generally safe

— Androgens (danazol) for HAE are contraindicated with liver disease

— Itraconazole used in CGD prophylaxis requires LFT monitoring and has drug interactions via CYP3A4

— Hepatitis B/C screening before IVIG; reactivation surveillance if biologics added

— Cumulative risk factors: age >65, immobility, prior VTE, atherosclerosis, high-dose IVIG

— Mitigate: split dose over 2 days, slower rate, IgA-depleted/low-osmolality product, hydration

— PCV20 (or PCV15 + PPSV23), annual influenza, RSV vaccine (≥60), recombinant zoster, Tdap

— Avoid live vaccines as in younger PID

Step 3 management: New hypogammaglobulinemia in a 65-year-old = order SPEP/UPEP, free light chains, chest CT (thymoma), peripheral smear before labeling primary. Board pearl: Good syndrome is the classic Step 3 "older adult with thymoma and recurrent sinopulmonary infections" trap.

Late-onset adult PID — older patient considerations:

Renal impairment considerations:

Hepatic impairment:

Thrombosis risk in elderly PID patients on IVIG:

Vaccination in elderly PID:

Special Populations — Pregnancy and Reproductive Considerations

— IgG actively transports across the placenta in T3 — maternal IgG trough should be maintained ≥600–800 mg/dL to protect the neonate

— IVIG/SCIG dosing typically increases 20–50% in pregnancy due to expanded volume and active transport

— More frequent trough monitoring (every 4–6 weeks)

— IVIG and SCIG are considered safe in pregnancy — pregnancy category historically B-equivalent

— Estrogen surge worsens attacks — anticipate increased frequency

— C1-INH concentrate (plasma-derived) is the first-line therapy for acute attacks and prophylaxis — safe in pregnancy

— Avoid androgens (danazol) — virilization of female fetus

— Tranexamic acid is sometimes used but second-line; lanadelumab data emerging

— Inactivated influenza, Tdap, COVID-19 — all recommended

— Avoid live vaccines (MMR, varicella, yellow fever) — both pregnancy and PID exclude

— Infants born to mothers with XLA carrier status or known monogenic PID — refer for newborn immune evaluation; newborn screening for SCID (TREC assay) catches T-cell defects

— Defer live vaccines in neonates of mothers on biologics until status clarified

— Breastfeeding is safe and recommended; maternal IVIG does not contraindicate

— Estrogen-containing contraception worsens HAE — use progestin-only or non-hormonal methods

— Genetic counseling for known monogenic forms (XLA, CGD, hyper-IgM are X-linked; CVID is mostly polygenic/sporadic)

— Step 3 systems issue: structured handoff from pediatric immunology to adult clinic — confirm dosing, infusion schedule, vaccine history, medication adherence

Key distinction: Estrogen worsens HAE; androgens were historically used therapeutically — but danazol is contraindicated in pregnancy; switch to C1-INH concentrate. Board pearl: Pregnant CVID patient — increase IVIG dose by ~25%, monitor trough monthly, expect neonate to be protected by transplacental IgG for ~6 months.

Pregnancy in women with antibody deficiency:

HAE in pregnancy:

Vaccination of pregnant PID patients:

Neonatal management:

Contraception and family planning:

Adolescent transition to adult care:

Complications and Adverse Outcomes

— Bronchiectasis — develops in 25–60% of CVID; cylindrical pattern, often lower lobe; consider chronic Pseudomonas colonization

— Chronic sinusitis with mucosal thickening, polyps, anosmia

— Recurrent pneumonia → respiratory failure, cor pulmonale

— Chronic enteroviral meningoencephalitis (XLA): subacute neurologic decline, CSF PCR positive

— Opportunistic infections in combined defects: PJP, CMV, disseminated fungal

— Granulomatous-lymphocytic interstitial lung disease (GLILD) — nodular interstitial pattern, often confused with sarcoid; treated with rituximab + azathioprine or MMF

— Autoimmune cytopenias: ITP, AIHA, Evans syndrome — treat with steroids, rituximab; avoid splenectomy if possible

— Enteropathy: sprue-like, nodular lymphoid hyperplasia, atrophic gastritis, B12 deficiency, chronic norovirus

— Splenomegaly with hypersplenism

— Granulomatous disease mimicking sarcoidosis — non-caseating granulomas in lungs, liver, spleen, lymph nodes

— Non-Hodgkin lymphoma — risk increased ~5–10× in CVID

— Gastric adenocarcinoma — risk 10× from atrophic gastritis and pernicious anemia; screen with EGD in symptomatic patients

— Skin cancers

— IVIG: thrombosis, AKI, hemolysis, aseptic meningitis, anaphylaxis (anti-IgA)

— Antibiotic prophylaxis: C. difficile, resistance emergence

— Long-term steroids for autoimmune complications: osteoporosis, diabetes, infection risk compounding

— Chronic disease burden, infusion fatigue, depression

— Sexual and reproductive concerns

Step 3 management: Any CVID patient with new persistent lymphadenopathy, B-symptoms, or LDH elevation → biopsy to exclude lymphoma — do not assume it's granulomatous disease. Board pearl: GLILD shortens survival in CVID more than infections do in the IVIG era — screen with surveillance HRCT every 2–3 years in symptomatic patients.

Infectious complications — major drivers of morbidity:

Non-infectious complications (especially in CVID — affect ~30%):

Malignancy:

Therapy-related complications:

Quality of life and mental health:

When to Escalate Care — ICU, Consult, and Inpatient Triage

— Sepsis with hemodynamic instability — PID patients decompensate faster with lower reserve

— Respiratory failure from pneumonia (PJP, viral, bacterial, fungal)

— Severe HAE attack with laryngeal involvement — secure airway, give C1-INH/icatibant immediately

— IVIG-related severe reaction: anaphylaxis, massive hemolysis, acute renal failure

— Encephalitis (enteroviral in XLA, JC virus PML in T-cell defects)

— Pneumonia with hypoxia, multilobar, or treatment failure

— Severe diarrhea with dehydration or chronic norovirus suspicion

— Febrile neutropenia in phagocytic defects

— New autoimmune cytopenia requiring transfusion or immunosuppression

— Initiation of IVIG in patients with active infection or high reaction risk

— Clinical immunology — diagnosis confirmation, replacement initiation, vaccine response interpretation

— Pulmonology — bronchiectasis management, suspected GLILD, lung biopsy

— Infectious disease — opportunistic or resistant infections, atypical mycobacteria

— Hematology/oncology — cytopenias, lymphoma workup, HSCT evaluation

— Gastroenterology — chronic diarrhea, suspected enteropathy, gastric cancer screening

— Genetics — counseling, panel selection, results interpretation

— Patients with T-cell defects require irradiated, CMV-negative, leukoreduced blood products to prevent transfusion-associated GVHD

— IgA-deficient patients with anti-IgA antibodies need washed RBCs or IgA-deficient donor products

— Early broad coverage but de-escalate with culture data

— Anti-pseudomonal coverage for bronchiectasis exacerbations

— PJP prophylaxis if CD4 <200 or T-cell defect: TMP-SMX

CCS pearl: In a CCS PID case with laryngeal angioedema unresponsive to epi/antihistamines, immediately order C1-INH concentrate or icatibant and prepare for fiberoptic intubation — clock penalties accrue rapidly. Board pearl: Always check IgA status before transfusing a patient with suspected antibody deficiency.

Immediate ICU triage in PID patient:

Inpatient admission criteria:

Consult triggers:

Transfusion safety:

Antibiotic stewardship:

Key Differentials — Other Causes of Recurrent Infection (Same Category)

— CVID — adult onset, low IgG + IgA/IgM, autoimmunity, GI disease, granulomas

— XLA (Bruton) — male, absent B cells, absent tonsils, presents in childhood but mild forms may present in young adulthood

— Selective IgA deficiency — usually asymptomatic; risk of anaphylaxis to blood products

— Specific antibody deficiency — normal IgG but failed vaccine response

— Hyper-IgM syndrome — recurrent sinopulmonary + opportunistic (PJP); CD40L defect

— IgG subclass deficiency — clinical relevance only with functional defect

— C1, C2, C4 — SLE-like syndromes + encapsulated infections

— C3 — severe pyogenic infections in childhood

— C5–C9, properdin, factor D — recurrent Neisseria

— MBL deficiency — generally mild

— Chronic granulomatous disease (CGD) — catalase-positive organisms (Staph aureus, Aspergillus, Serratia, Burkholderia, Nocardia); diagnosis via DHR flow assay

— Leukocyte adhesion deficiency — delayed cord separation, leukocytosis, no pus

— Chédiak-Higashi — albinism, giant granules, recurrent infections

— Severe congenital neutropenia, cyclic neutropenia

— DiGeorge (22q11.2) — adult mild forms with hypocalcemia, cardiac history, mild T-cell dysfunction

— Hyper-IgE (Job) syndrome — STAT3 LOF; eczema, cold abscesses, retained teeth, fractures

— Ataxia-telangiectasia — cerebellar ataxia, oculocutaneous telangiectasias, IgA deficiency, lymphoma

— GATA2 deficiency — MonoMAC, NK/B-cell lymphopenia, MDS risk

Key distinction: Pattern of organism = pattern of defect. Encapsulated bacteria → humoral or complement (Neisseria specifically → terminal complement). Catalase-positive → phagocyte (CGD). PJP/CMV/fungal → T-cell or combined. Board pearl: Lupus-like syndrome + recurrent encapsulated infections in an adolescent/young adult → C1q or C2 complement deficiency.

Within primary immunodeficiency, differentiate by infection pattern:

Humoral (antibody) deficiencies:

Complement deficiencies:

Phagocytic disorders:

T-cell / combined:

Key Differentials — Secondary Immunodeficiency and Mimics

— HIV/AIDS — always test; can present identically to PID

— Chronic CMV, EBV-driven lymphoproliferation

— Disseminated tuberculosis

— Rituximab (anti-CD20) — can cause prolonged hypogammaglobulinemia lasting years after last dose

— Anti-epileptics: phenytoin, carbamazepine, valproate, lamotrigine

— Chronic corticosteroids (>20 mg prednisone equivalent)

— Mycophenolate mofetil, methotrexate, cyclophosphamide

— Belimumab, ocrelizumab, ofatumumab

— Captopril, sulfasalazine (rare)

— Multiple myeloma — paradoxically low uninvolved immunoglobulins

— CLL — most common cause of hypogammaglobulinemia in elderly

— Lymphoma, especially after chemotherapy

— Thymoma → Good syndrome — hypogammaglobulinemia + recurrent infection + diarrhea

— Post-HSCT immunodeficiency

— Nephrotic syndrome — albumin low, IgG lost in urine, IgM preserved (too large to filter)

— Protein-losing enteropathy (lymphangiectasia, IBD, Whipple)

— Severe burns, exfoliative skin disease

— Diabetes mellitus — recurrent skin, urinary, mucocutaneous infections

— Splenectomy/asplenia/sickle cell — encapsulated organism susceptibility (post-splenectomy sepsis)

— Malnutrition, alcoholism, cirrhosis — generalized immune dysfunction

— Aging immunosenescence — declining response but not true PID

Step 3 management: Algorithm for low IgG in an adult: (1) HIV, (2) medication review especially rituximab, (3) SPEP/UPEP + free light chains, (4) albumin + UA for protein loss, (5) chest CT for thymoma, (6) only then consider primary. Board pearl: A patient with chronic phenytoin use who develops recurrent sinopulmonary infections — switch the anticonvulsant before diagnosing CVID.

Secondary immunodeficiencies must be excluded before labeling "primary" — they are vastly more common in adults.

Infectious:

Medication-induced hypogammaglobulinemia:

Malignancy-associated:

Protein loss:

Other:

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Immunoglobulin replacement indefinitely with quarterly trough monitoring

— Target IgG trough 700–800 (general) or ≥800–1000 (bronchiectasis or active infection)

— Patient-preferred route (IVIG vs SCIG) revisited yearly

— Indicated when breakthrough infections despite adequate IgG trough or in bronchiectasis

— Azithromycin 250 mg three times weekly — anti-inflammatory + antimicrobial

— Rotating regimens to limit resistance

— Annual influenza (inactivated, not nasal)

— PCV20 once OR PCV15 followed by PPSV23 ≥1 year later

— Tdap every 10 years

— Recombinant zoster (Shingrix) at age ≥50

— RSV vaccine ≥60 (or ≥50 with risk factors)

— Hepatitis B if not immune

— COVID-19 boosters per current schedule

— Avoid all live vaccines

— Annual or biannual labs: CBC, CMP, immunoglobulins, vaccine titers (pre-IVIG history dependent)

— Surveillance HRCT every 2–3 years in CVID with prior lung disease

— EGD if dyspepsia, anemia, or B12 deficiency — gastric cancer risk

— Pulmonary function tests annually

— Bone density (osteoporosis risk from steroids, vitamin D status)

— Smoking cessation — accelerates bronchiectasis

— Hand hygiene, mask use during outbreaks

— Food safety (avoid raw eggs, unpasteurized dairy, deli meats in T-cell defects)

— Pet counseling (avoid reptiles, exotic pets in phagocyte/T-cell defects)

— Travel medicine consultation — live vaccines (yellow fever) contraindicated

— IVIG/SCIG is expensive; specialty pharmacy navigation, prior authorizations

— Patient assistance programs through manufacturers and IDF

Board pearl: No live vaccines in CVID; Shingrix is recombinant and safe and recommended. Step 3 management: Annual flu shot, PCV20, and Shingrix at ≥50 — these are the discharge-summary vaccines for CVID.

Core long-term management of adult antibody deficiency:

Antibiotic prophylaxis options:

Vaccination schedule (inactivated only):

Cancer and complication surveillance:

Lifestyle and patient education:

Insurance and access:

Follow-Up, Monitoring Parameters, and Rehab/Counseling

— First 6 months: IgG trough before each infusion (or monthly for SCIG) to confirm steady state

— Renal function and LFTs before each of the first 3 infusions, then quarterly

— CBC quarterly to monitor for hemolysis or cytopenias

— Annual: vaccine titers (pre-immunoglobulin levels lost meaning post-replacement), HIV/HCV/HBV surveillance per product safety, PFTs, HRCT every 2–3 years if lung disease

— Patient diary of infections, antibiotic courses, missed work

— Reduction in infection frequency by ≥50% is a reasonable benchmark of adequacy

— Airway clearance for bronchiectasis: chest physiotherapy, oscillating PEP devices (Acapella, Flutter), hypertonic saline nebulization

— Pulmonary rehab program for deconditioning

— Sputum cultures every 3–6 months — track Pseudomonas colonization, NTM

— Screen for depression and anxiety; chronic disease + lifelong therapy is burdensome

— Connect with Immune Deficiency Foundation (IDF) for patient resources, peer support

— Vocational counseling — many patients can self-administer SCIG at home preserving work capacity

— Adolescent-to-adult transition: structured handoff with documented PID diagnosis, infusion regimen, vaccine record

— Hospital discharge after exacerbation: confirm next IVIG dose, antibiotic completion, PCP follow-up within 1–2 weeks, pulmonology follow-up within 4 weeks

— Medication reconciliation flags: ensure outpatient immunoglobulin schedule isn't interrupted by admission

— Sick-day rules: fever ≥38.3°C → call provider, low threshold for cultures

— Avoid sick contacts, daycare exposure

— Travel: pretravel consultation; ensure adequate IVIG supply; carry medical letter for needles/medications

Step 3 management: After hospital discharge for CVID pneumonia, schedule PCP follow-up in 7–14 days, confirm next scheduled IVIG infusion isn't delayed, and reinforce airway clearance. CCS pearl: Always order sputum culture in CVID with bronchiectasis exacerbation — chronic Pseudomonas colonization changes antibiotic choice.

Monitoring cadence after IVIG/SCIG initiation:

Symptom tracking:

Pulmonary rehabilitation:

Psychosocial:

Transitions of care (Step 3 emphasis):

Counseling content:

Ethical, Legal, and Patient Safety Considerations

— PID gene panels and WES may identify incidental findings (cancer susceptibility, late-onset neurodegenerative variants)

— Pre-test counseling must cover scope, possible results, implications for family members, and GINA (Genetic Information Nondiscrimination Act) protections — note GINA does not cover life, disability, or long-term care insurance

— Document patient preference about return of secondary findings

— When monogenic PID identified (XLA, CGD, hyper-IgM), recommend testing of at-risk relatives — but respect their autonomy; do not bypass the proband to contact relatives directly

— Hospital discharge with interrupted IVIG schedule → infection risk

— Adolescent transition without warm handoff → loss to follow-up, missed diagnoses

— Change of insurance/specialty pharmacy → therapy gap

— Mitigation: structured medication reconciliation, single point-of-contact case manager, written care plans

— Inadvertent administration of live vaccines (MMR, yellow fever, BCG, nasal flu) to a PID patient is a never event

— Build EHR allergy/precaution flags

— Educate patient to inform every provider before any vaccine

— IgA-deficient patient receiving non-washed product → anaphylaxis

— T-cell deficient patient receiving non-irradiated blood → fatal transfusion-associated GVHD

— Document immunodeficiency clearly in chart and on transfusion order

— Some opportunistic infections (TB, certain meningitis cases, measles) are reportable

— HIV must be reported per state law — establishes secondary cause

— IVIG shortages have occurred; prioritization frameworks favor patients with documented antibody deficiency and active infection over off-label uses

— Patient advocacy when insurance denies indicated therapy

Board pearl: Documenting anti-IgA antibody status in an IgA-deficient patient before transfusion is a Step 3-tested safety issue. Step 3 management: A patient with newly diagnosed XLA gets a flu shot — confirm it was inactivated injectable, not live nasal (FluMist); the latter is contraindicated.

Informed consent for genetic testing:

Family screening:

Transitions of care — high-risk handoff points:

Vaccination errors — patient safety:

Transfusion safety:

Mandatory reporting and public health:

Resource and access ethics:

High-Yield Associations and Rapid-Fire Clinical Facts

— Encapsulated (S. pneumoniae, H. influenzae) → humoral or asplenia

— Neisseria recurrent → terminal complement (C5–C9) or properdin

— PJP, CMV, disseminated fungal → T-cell/combined

— Catalase-positive (Staph aureus, Serratia, Burkholderia, Nocardia, Aspergillus) → CGD

— Disseminated NTM/salmonella → IFN-γ/IL-12 axis

— Severe HSV/VZV → NK-cell, TLR3

— Giardia, enterovirus chronic → humoral

— Absent tonsils + low all-Ig + male → XLA

— Thymoma + hypogammaglobulinemia → Good syndrome

— Eczema + cold abscesses + retained teeth + ↑IgE → Hyper-IgE (Job)

— Ataxia + telangiectasias + ↓IgA + lymphoma → A-T

— Recurrent angioedema, no urticaria, no response to antihistamines → HAE

— Albinism + recurrent infections + giant granules → Chédiak-Higashi

— Tetany + cardiac defect + T-cell low + chromosome 22q11 → DiGeorge

— MonoMAC, MDS, NTM → GATA2 deficiency

— Lupus-like + recurrent encapsulated → C1q/C2 deficiency

— Low IgG + failed vaccine response after Pneumovax challenge = antibody deficiency

— DHR flow = CGD

— CH50 zero → classical pathway; AH50 zero → alternative

— Both CH50 and AH50 abnormal → C3 or terminal common pathway

— IgG trough target: ≥700 (general), ≥800–1000 (bronchiectasis)

— IVIG reaction triad to know: thrombosis, AKI, hemolysis

— HAE acute: C1-INH, icatibant, ecallantide — NOT epi/steroids/antihistamines

— CGD prophylaxis: TMP-SMX + itraconazole + IFN-γ

— PJP prophylaxis: TMP-SMX

— Lymphoma risk ~5–10× — biopsy any persistent lymphadenopathy

— Gastric adenocarcinoma — low threshold for EGD

Board pearl: When you see "bronchiectasis + low IgG + autoimmune cytopenia + granulomas" — CVID is the answer. Key distinction: A normal IgG with failed pneumococcal vaccine response = specific antibody deficiency, still treated.

Pathogen → defect mapping (memorize):

Syndromic pearls:

Diagnostic shortcuts:

Therapy quickies:

Cancer surveillance in CVID:

Board Question Stem Patterns

"A 32-year-old woman with recurrent sinusitis (4 episodes/year), 2 pneumonias in the past year, and chronic diarrhea has IgG 380, IgA 12, IgM 28. Pneumococcal titers fail to rise after PPSV23. HIV negative." → Answer: CVID; start IVIG.

"A 22-year-old man with recurrent otitis since childhood, absent tonsils, IgG 80, IgA 5, IgM 10, B cells <1%." → XLA, start IVIG.

"A 19-year-old with 3 episodes of meningococcal meningitis. Which test?" → CH50 and AH50. Vaccinate against meningococcal serogroups including B; consider prophylactic penicillin.

"A 62-year-old with new hypogammaglobulinemia, recurrent pneumonia, and anterior mediastinal mass on CT." → Thymoma + Good syndrome. Resect thymoma, start IVIG.

"Recurrent lip and laryngeal swelling without urticaria, no response to epi/diphenhydramine/steroids; mother had similar episodes." → HAE; check C4 (low) then C1-INH level/function. Acute: C1-INH, icatibant.

"A 55-year-old on rituximab for RA for 3 years presents with recurrent sinusitis, IgG 350." → Rituximab-induced hypogammaglobulinemia, not CVID.

"A patient with newly diagnosed CVID is offered the live attenuated zoster vaccine." → Contraindicated; use recombinant Shingrix.

"A young adult with recurrent Serratia liver abscess and Aspergillus pneumonia." → CGD; DHR flow assay; prophylaxis with TMP-SMX + itraconazole + IFN-γ.

"Patient on IVIG develops flank pain, dark urine, Hgb drop." → IVIG-induced hemolysis from anti-A/B isohemagglutinins.

"IgA-deficient patient needs RBCs." → Washed RBCs or IgA-deficient donor product.

Step 3 management: Across all stems, the management answer is usually (1) confirm the defect, (2) exclude secondary causes, (3) start replacement or targeted therapy, (4) vaccinate (inactivated only), (5) coordinate longitudinal care. Board pearl: "Failure to mount vaccine response" is often the test-question fingerprint of antibody deficiency.

Stem 1 — Classic CVID:

Stem 2 — XLA late catch:

Stem 3 — Terminal complement:

Stem 4 — Good syndrome:

Stem 5 — HAE:

Stem 6 — Secondary cause trap:

Stem 7 — Vaccine pitfall:

Stem 8 — CGD:

Stem 9 — IVIG complication:

Stem 10 — Transfusion safety:

One-Line Recap

Adult primary immunodeficiency should be suspected in any patient with recurrent, severe, persistent, or unusual infections — especially with bronchiectasis, autoimmunity, or family history — and workup begins with HIV testing, quantitative immunoglobulins, vaccine response titers, and exclusion of secondary causes before targeted classification and lifelong immunoglobulin replacement or condition-specific therapy.

Board pearl: When in doubt on Step 3, the move is quantitative immunoglobulins + HIV + vaccine titers before any specialist referral — those four data points organize the entire differential and the next management step.

Suspicion triggers: ≥2 pneumonias/year, ≥4 sinusitis episodes/year, recurrent encapsulated organism infection, opportunistic pathogens, bronchiectasis without obvious cause, autoimmune cytopenias + infections, recurrent Neisseria, family history, angioedema unresponsive to antihistamines.

Workup ladder: CBC + CMP + HIV + quantitative IgG/IgA/IgM/IgE → pneumococcal/tetanus titers ± PPSV23 challenge → lymphocyte subsets and complement (CH50/AH50) as indicated → HRCT chest if pulmonary → genetic panel for syndromic features → always exclude secondary causes (rituximab, anti-epileptics, myeloma/CLL, thymoma, protein loss, HIV).

Management essentials: Immunoglobulin replacement targeting IgG trough ≥700 (≥800–1000 with bronchiectasis), inactivated-only vaccines (avoid all live vaccines; Shingrix is safe and recommended), antibiotic prophylaxis when needed, condition-specific therapies (C1-INH for HAE, TMP-SMX/itraconazole/IFN-γ for CGD), and surveillance for lymphoma, gastric cancer, and GLILD.

Safety/systems pearls: Document IgA-deficient and T-cell defect status in chart to prevent transfusion catastrophe (use washed/IgA-deficient + irradiated CMV-negative leukoreduced products); never give live vaccines; ensure seamless IVIG continuity across transitions of care; counsel on GINA limitations before genetic testing; refer at-risk family members for screening with appropriate consent.