Respiratory

Latent TB infection: screening and chemoprophylaxis

Clinical Overview and When to Suspect Latent TB Infection

— Foreign-born from high-prevalence regions (Asia, Africa, Latin America, Eastern Europe, Russia)

— Residents/employees of congregate settings: correctional facilities, homeless shelters, long-term care, nursing homes

— Healthcare workers with patient contact

— Close contacts of a person with active pulmonary TB

— Immunosuppressed: HIV, TNF-α inhibitor candidates, transplant recipients, chronic steroids (≥15 mg/day prednisone ≥1 month), chemotherapy

— Patients with silicosis, ESRD on dialysis, diabetes, gastrectomy/jejunoileal bypass, head/neck cancer, untreated fibrotic lesions on CXR

— IV drug users

Board pearl: Do not screen low-risk patients — a positive test in a low-prevalence population has poor positive predictive value, and the harms of unnecessary hepatotoxic therapy outweigh benefits. The screening decision itself is the test of Step 3 reasoning: target, then test, then treat.

Definition: Latent TB infection (LTBI) = persistent immune response to Mycobacterium tuberculosis antigens without clinical, bacteriologic, or radiographic evidence of active disease. Patients are asymptomatic, non-contagious, and have a ~5–10% lifetime risk of reactivation (highest in the first 2 years after exposure).

Epidemiology in the US: ~13 million people harbor LTBI. The vast majority of new active TB cases arise from reactivation of LTBI, so the 2016 USPSTF Grade B recommendation focuses screening on asymptomatic adults at increased risk — not population-wide.

Whom to screen (targeted testing = intent to treat):

When to suspect active TB instead (and stop the LTBI workflow): cough >2–3 weeks, hemoptysis, night sweats, weight loss, fevers, or abnormal CXR. Active disease must be excluded before initiating LTBI therapy because monotherapy in active TB selects for resistance.

Presentation Patterns and Key History

— New immigrant establishing primary care

— Healthcare worker annual screen or pre-employment

— Pre-biologic screening (psoriasis, RA, IBD before infliximab/adalimumab/etanercept)

— Newly diagnosed HIV — TB screening is part of the initial workup regardless of CD4

— Contact investigation after a household or workplace TB exposure

— Pre-transplant or pre-chemotherapy evaluation

— Dialysis initiation or nursing home admission screen

— Country of birth and residence history (>1 month in high-burden country)

— Prior TB exposure, prior positive PPD/IGRA, prior treatment (document regimen and completion)

— BCG vaccination history — affects TST interpretation but not IGRA

— Symptoms suggestive of active TB (the "review of systems for TB": cough, fever, night sweats, weight loss, hemoptysis, anorexia)

— HIV status, diabetes, CKD, malignancy, immunosuppressants, alcohol use, hepatitis B/C

— Pregnancy status and breastfeeding

— Current medications, especially hepatotoxic drugs and rifamycin interactions (OCPs, warfarin, methadone, protease inhibitors)

Step 3 management: Before ordering any LTBI test, ask yourself: "If positive, will I treat?" If the answer is no, do not test. This is the cornerstone of targeted tuberculin testing and avoids the cascade of unnecessary CXRs, LFTs, and patient anxiety. The history visit is where the screening decision is finalized.

Core principle: LTBI is, by definition, asymptomatic. The "presentation" is almost always a positive screening test in an at-risk patient, an abnormal CXR incidentally found, or pre-treatment screening before immunosuppression.

Common Step 3 vignette setups:

Key history elements to elicit:

Exposure risk stratification matters for TST cutoffs (5 vs 10 vs 15 mm) — see Chunk 4.

Physical Exam Findings (and Hemodynamic Assessment)

— General: weight, BMI trend, cachexia, temperature (low-grade fevers in active TB)

— HEENT: cervical/supraclavicular lymphadenopathy (scrofula suggests extrapulmonary TB)

— Pulmonary: auscultate for apical crackles, consolidation, post-tussive rales, decreased breath sounds (effusion); active pulmonary TB classically affects upper lobes

— Cardiac: baseline assessment; pericardial rub is rare but indicates TB pericarditis

— Abdominal: hepatosplenomegaly (disseminated/miliary TB, HIV co-infection); ascites in peritoneal TB

— Skin: erythema nodosum (a hypersensitivity phenomenon), prior BCG scar on left deltoid, lupus vulgaris

— MSK/spine: vertebral tenderness, kyphosis (Pott disease), cold abscess

— Neuro: cranial nerve deficits, meningismus (TB meningitis) — rare but catastrophic to miss

Key distinction: Any abnormal pulmonary, lymphatic, or constitutional finding on exam upgrades the workup from "LTBI evaluation" to "rule out active TB" — which mandates sputum AFB smear ×3, NAAT, and culture, plus respiratory isolation if hospitalized, before any single-drug therapy.

Expected exam in LTBI: Entirely normal. There are no physical findings of latent TB itself — abnormal findings should redirect the workup toward active disease or an alternative diagnosis.

Targeted exam to rule out active TB before treating LTBI:

Document the TST induration measurement transversely across the forearm in millimeters at 48–72 hours. Measure induration, not erythema. A flat erythematous patch is a negative test regardless of size.

BCG scar inspection: A small, round, hypopigmented scar on the left deltoid suggests prior BCG. Recall that BCG does not invalidate the TST — it modestly reduces specificity but does not affect IGRA.

Diagnostic Workup — Initial Tests: TST vs IGRA, CXR, HIV

— Tuberculin Skin Test (TST/Mantoux): 0.1 mL PPD intradermal, read 48–72 h, measure induration in mm. Three cutoffs:

◦ ≥5 mm positive: HIV+, recent TB contact, fibrotic CXR changes consistent with prior TB, organ transplant, immunosuppression (≥15 mg prednisone ≥1 month, TNF-α inhibitors)

◦ ≥10 mm positive: Recent immigrants (<5 years) from high-prevalence countries, IV drug users, mycobacteriology lab personnel, congregate setting residents/employees, high-risk comorbidities (DM, CKD, silicosis, gastrectomy, leukemia/lymphoma, head/neck cancer), children <4 years, children exposed to high-risk adults

◦ ≥15 mm positive: Persons with no known risk factors (who arguably shouldn't have been tested)

— Interferon-Gamma Release Assay (IGRA): QuantiFERON-TB Gold Plus or T-SPOT.TB; single blood draw, results <24 h, no return visit, unaffected by prior BCG

— Chest X-ray (PA and lateral) to exclude active pulmonary TB — apical fibronodular scarring, cavitation, or infiltrate triggers sputum workup

— HIV testing if status unknown — co-infection changes everything

— Symptom screen documented in chart

Board pearl: A negative TST or IGRA does not rule out TB infection in the immunosuppressed or in recent exposure within the 8–10 week window period. Repeat testing 8–10 weeks after the last exposure for contacts initially negative. The two-step TST (boosted reaction) is used at baseline in serial-testing programs (healthcare, nursing home staff) to distinguish booster effect from new conversion.

Two acceptable screening modalities — either is appropriate per CDC; choose based on context:

CDC prefers IGRA in: BCG-vaccinated patients and those unlikely to return for TST reading (homeless, IVDU, healthcare workers)

TST preferred in: Children <5 years (data more robust), serial testing programs where IGRA variability is a concern

Mandatory next steps if screening test is positive:

Diagnostic Workup — Advanced and Confirmatory Studies

— Sputum AFB smear and culture ×3 specimens collected ≥8 hours apart, with at least one early-morning specimen

— Nucleic acid amplification test (NAAT) — Xpert MTB/RIF on at least one sputum sample; detects M. tuberculosis DNA and rifampin resistance within hours

— Mycobacterial culture remains gold standard (4–8 weeks); allows drug susceptibility testing

— Respiratory isolation (negative-pressure room, N95) until 3 negative AFB smears

— Chest CT if CXR equivocal — better for detecting tree-in-bud, miliary pattern, cavitation, mediastinal adenopathy

— Calcified granulomas and hilar calcifications without active disease support healed primary TB (Ranke complex = Ghon focus + calcified hilar node)

— AST, ALT, bilirubin, alkaline phosphatase — for all patients on isoniazid or rifamycin; mandatory in: pregnancy/postpartum (≤3 months), chronic liver disease, alcohol use, HIV, age >35 (some sources >50 with isoniazid)

— CBC and platelet count if rifampin used (rare thrombocytopenia)

— HIV test, hepatitis B and C serologies

— Pregnancy test in women of reproductive age

— Vision baseline if ethambutol considered (not used in LTBI, but relevant if regimen modified)

Step 3 management: A positive IGRA in a TNF-α inhibitor candidate with normal CXR and no symptoms = LTBI. Start chemoprophylaxis before initiating biologic, and complete at least 1 month of treatment prior to the first biologic dose when feasible. Document this clearly in the chart — it's a common malpractice pitfall.

When CXR is abnormal or symptoms suggest active TB:

Imaging adjuncts:

Discordant tests (TST+/IGRA− or vice versa): In low-risk patients with one positive test, the negative test takes precedence — generally do not treat. In high-risk patients, treat based on the positive result. In immunocompromised, indeterminate IGRA is common; repeat or use alternative test.

Pre-treatment baseline labs before LTBI therapy:

Risk Stratification and Treatment Decision Logic

— Recent contacts of active pulmonary TB (especially within 2 years)

— HIV-positive patients regardless of CD4

— Recent immigrants <5 years from endemic regions

— Patients about to start TNF-α inhibitors, JAK inhibitors, organ transplant, dialysis, or chemotherapy

— Children <5 with positive test

— Fibrotic changes on CXR consistent with old, untreated TB

— Recent tuberculin converters (>10 mm increase in 2 years)

— Active hepatitis or transaminases >3× ULN with symptoms or >5× ULN without symptoms

— Heavy alcohol use (counsel cessation; consider deferral)

— Pregnancy: not an absolute contraindication, but if low reactivation risk, often defer until 2–3 months postpartum

— Prior completed appropriate course — generally not retreated unless reinfection documented

— Discuss 1–3% risk of clinically significant hepatotoxicity with INH

— Discuss duration commitment (3–9 months depending on regimen)

— Discuss drug interactions, especially rifamycins with OCPs and antiretrovirals

— Document informed consent

Key distinction: Targeted testing implies intent to treat. If a patient declines treatment in advance, weigh whether testing adds value. However, for healthcare workers and immunosuppression candidates, testing is often mandated regardless — a true Step 3 ethical nuance where institutional policy and patient autonomy intersect. Always document the discussion and the patient's preferences before ordering screening tests in borderline cases.

Once LTBI is confirmed (positive test + active TB excluded + CXR clear), the default is to treat — unless contraindications exist. Treatment reduces reactivation risk by 60–90%.

Highest-priority groups for treatment (greatest absolute benefit):

Relative contraindications / caution:

Shared decision-making elements:

Pharmacotherapy — First-Line LTBI Regimens

— 3HP — Isoniazid + Rifapentine weekly × 12 weeks (12 doses)

◦ INH 15 mg/kg (max 900 mg) + rifapentine 900 mg, once weekly

◦ Originally DOT-only; self-administered now acceptable in adults and children ≥2 years

◦ Avoid in pregnancy, HIV on incompatible ART, <2 years old

— 4R — Rifampin daily × 4 months

◦ 10 mg/kg (max 600 mg) daily

◦ Preferred when INH resistance suspected, INH intolerance, or hepatotoxicity concerns

◦ Multiple drug interactions via CYP3A4 induction

— 3HR — Isoniazid + Rifampin daily × 3 months

◦ Acceptable alternative, especially in children

— 6H or 9H — Isoniazid monotherapy × 6 or 9 months

◦ 5 mg/kg adult (max 300 mg) or 10–20 mg/kg pediatric daily

◦ 9 months more effective than 6; historic standard but lower completion rates (~30–60%)

◦ Co-administer pyridoxine (vitamin B6) 25–50 mg daily in: pregnancy, breastfeeding, HIV, diabetes, alcohol use, malnutrition, CKD, seizure disorder — to prevent peripheral neuropathy

— Monthly clinical visits for symptom check: nausea, anorexia, RUQ pain, dark urine, jaundice, rash, neuropathy

— Monthly LFTs only if baseline abnormal, age >35–50, alcohol use, pregnancy/postpartum, HIV, hep B/C

— Stop INH if ALT >3× ULN with symptoms or >5× ULN without

— Counsel that rifampin/rifapentine turns secretions orange — tears, urine, sweat; permanently stains contact lenses

Board pearl: 3HP is now first-line for most LTBI patients. Short duration dramatically improves completion. Memorize the "3HP, 4R, 3HR, 9H" hierarchy — exam loves the contemporary shift away from 9H monotherapy.

CDC/NTCA 2020 preferred "short-course" regimens (better completion rates, less hepatotoxicity than 9H):

Alternative regimen:

Drug-specific monitoring:

Expanded Pharmacology — Interactions, Resistance, and Special Situations

— Hormonal contraceptives: decreased efficacy — advise barrier or non-hormonal method (copper IUD, depot)

— Warfarin: INR drops; increase dose or switch anticoagulant

— Methadone: opioid withdrawal — increase dose

— Direct-acting antivirals for HCV, DOACs, statins (simvastatin, atorvastatin), azoles, calcineurin inhibitors (tacrolimus, cyclosporine), certain antiepileptics

— HIV ART: Rifampin contraindicated with most PIs and many INSTIs; rifabutin is the rifamycin of choice in HIV. With dolutegravir, increase dolutegravir to twice daily if using rifampin; avoid rifampin with bictegravir, elvitegravir, rilpivirine

— Inhibits CYP isoenzymes — increases phenytoin, carbamazepine, warfarin, theophylline levels

— Hepatotoxicity: age-related risk, additive with alcohol, rifampin, acetaminophen

— Peripheral neuropathy — give pyridoxine in at-risk patients

— Drug-induced lupus, sideroblastic anemia, optic neuritis (rare)

— Source case with documented INH-monoresistant TB → use 4R (rifampin alone)

— Consult infectious disease/public health; individualized regimens often levofloxacin- or moxifloxacin-based × 6–12 months; no single CDC-preferred MDR-LTBI regimen

— Pill counts, app-based DOT, weekly dosing (3HP) favored for poor adherence

— Public health DOT for high-risk patients

Step 3 management: A 32-year-old on combined OCPs starting rifampin → counsel that pill becomes unreliable; recommend a non-hormonal backup or switch to 4R-alternative regimen 3HR is not a solution (still contains rifampin). Use 9H with pyridoxine if hormonal contraception preservation is critical, or transition to non-CYP-inducing method. Document counseling.

Rifamycin drug interactions (rifampin > rifapentine > rifabutin as CYP3A4 inducers):

Isoniazid interactions and adverse effects:

Suspected INH-resistant exposure:

Suspected MDR-TB contact:

Adherence support tools:

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher INH hepatotoxicity risk — rates approach 2–5% in patients >50; consider 4R or 3HP over 9H

— Polypharmacy raises interaction risk with rifamycins (warfarin, statins, antihypertensives)

— Reactivation risk is elevated in this group, especially in long-term care facilities — outbreaks documented

— Baseline and monthly LFTs strongly recommended

— CXR threshold lower — apical fibrosis common; if any doubt, obtain sputum studies before chemoprophylaxis

— ESRD increases reactivation risk 10–25×; screen at dialysis initiation

— IGRA preferred — fewer indeterminate results than TST in uremia, but both can be falsely negative due to anergy

— No dose adjustment needed for INH, rifampin, rifapentine in CKD/HD (all primarily hepatically cleared)

— Pyridoxine 50 mg daily mandatory with INH in dialysis patients (neuropathy risk)

— Schedule dosing after hemodialysis on dialysis days

— Child-Pugh A: proceed with caution; baseline + monthly LFTs

— Child-Pugh B/C: defer LTBI treatment unless extremely high reactivation risk; consult hepatology and ID

— Active hepatitis B or C: not an absolute contraindication; treat hepatitis first when possible, then LTBI with rifampin-based regimen (lower hepatotoxicity than INH in some data) and tight LFT monitoring

— Stop drug for ALT >3× ULN with symptoms or >5× ULN asymptomatic; rechallenge with single agent after normalization

— Counsel cessation; concurrent heavy drinking is a relative contraindication

— Consider deferring treatment until alcohol-free; if treating, monthly LFTs and close follow-up

Board pearl: In an 80-year-old nursing home resident with a newly positive TST after a facility outbreak, 4R is preferred over 9H — shorter, better tolerated, fewer drug interactions if monitored carefully, and dramatically higher completion rates.

Elderly (>65 years):

Chronic kidney disease and dialysis:

Hepatic impairment:

Alcohol use disorder:

Special Populations — Pregnancy, Pediatrics, and HIV

— LTBI testing is safe in pregnancy (TST and IGRA both acceptable)

— Treatment timing: If low reactivation risk (e.g., remote conversion in non-immunocompromised) — defer until 2–3 months postpartum

— High-risk situations (recent contact, HIV+, recent immigrant) — treat during pregnancy

— Preferred regimen: INH daily × 9 months with pyridoxine 25–50 mg daily

— 3HP is NOT recommended in pregnancy (insufficient safety data)

— Rifampin is acceptable in pregnancy if INH not tolerated

— Increased hepatotoxicity in postpartum period — monitor LFTs monthly through 3 months postpartum

— Breastfeeding is safe on INH and rifampin; infant should also receive pyridoxine if breastfeeding mother on INH

— TST preferred in children <5; IGRA acceptable ≥2 years per AAP

— Cutoff ≥10 mm in children <4 or with risk factors; ≥5 mm in immunocompromised or contacts

— Regimens:

◦ 3HP for ages ≥2 years (preferred when feasible)

◦ 4R daily × 4 months for any age (well tolerated)

◦ 3HR daily × 3 months — widely used pediatric option

◦ 9H if other regimens unavailable, with pyridoxine for breastfeeding infants and adolescents

— Children <5 with TB exposure but negative initial test: "window prophylaxis" with INH; repeat test 8–10 weeks after last exposure; stop if still negative

— Test all HIV+ patients at diagnosis; repeat annually if ongoing risk

— Treat any positive test regardless of CD4

— 3HP weekly × 12 weeks is preferred and now acceptable with dolutegravir or efavirenz-based ART

— Avoid rifampin with most boosted PIs and many INSTIs; use rifabutin as substitute

— Continue ART throughout

Step 3 management: Pregnant woman with positive IGRA, recent close contact with smear-positive household member → start INH + pyridoxine now, don't defer; reactivation risk is too high to wait until postpartum.

Pregnancy:

Pediatrics:

HIV co-infection:

Complications and Adverse Outcomes

— Most reactivation occurs within first 2 years post-conversion

— Presents as pulmonary TB (cough >3 weeks, hemoptysis, weight loss, night sweats, apical cavitation) or extrapulmonary disease (lymphadenitis, pleural, GU, skeletal, miliary, meningitis)

— Mortality of untreated active TB approaches 50%; even with treatment, 5–10%

— INH: ~0.1–0.6% symptomatic hepatitis; rare fulminant hepatic failure

— Risk factors: age >35, alcohol, hepatitis B/C, pregnancy/postpartum, concurrent hepatotoxins

— Present with anorexia, nausea, RUQ pain, jaundice, dark urine, fatigue

— Stop drug immediately if symptomatic with ALT >3× ULN or asymptomatic ALT >5× ULN

— INH-induced via pyridoxine depletion; preventable with B6 25–50 mg daily in at-risk patients

— Distal symmetric burning, paresthesias

— Orange discoloration of body fluids (benign, counsel)

— Flu-like syndrome (especially with intermittent dosing of rifapentine)

— Thrombocytopenia, hemolytic anemia, acute interstitial nephritis (rare)

— Drug interactions causing therapeutic failure of other meds (see Chunk 8)

— Rash, fever, eosinophilia; rare DRESS, SJS/TEN with INH

Key distinction: Mild asymptomatic transaminase elevation (1–3× ULN) on INH is common (10–20%) and does not require discontinuation — continue with closer monitoring. Stopping prematurely for trivial bumps causes incomplete treatment courses and reactivation — a tested nuance.

Reactivation TB (failure of prophylaxis or untreated LTBI):

Hepatotoxicity (most clinically important LTBI treatment complication):

Peripheral neuropathy:

Rifamycin adverse effects:

Hypersensitivity reactions:

Drug-induced lupus (INH): ANA positive, arthralgias, serositis; resolves on discontinuation

Optic neuritis: rare with INH; more concerning with ethambutol (not used in LTBI)

Public health failure: missed contact tracing, untreated source cases → ongoing transmission

When to Escalate Care — Consult and Inpatient Triage

— Active TB cannot be excluded (symptoms, abnormal CXR, AFB+ sputum) — admit to negative-pressure isolation, notify infection control, public health, and ID consult

— Severe drug-induced hepatitis (ALT >5× ULN with symptoms, jaundice, coagulopathy) — stop drug, admit if INR elevated, hepatic encephalopathy, or unable to tolerate PO

— DRESS, SJS/TEN, severe hypersensitivity — admit, dermatology and allergy consult, stop drug, supportive care

— Suspected MDR or XDR exposure — ID consult mandatory before regimen selection

— Infectious Diseases: drug resistance, treatment failure, complex co-morbidities, MDR contacts, severe drug intolerance, pediatric or pregnant complex cases, organ transplant candidates

— Hepatology: baseline cirrhosis, drug-induced liver injury, hepatitis B/C co-management

— Public health department: mandatory reporting of all confirmed TB cases (LTBI is not universally reportable but is in some jurisdictions — check state law); contact investigation

— Occupational health: healthcare worker conversions

— Order CXR (PA and lateral), HIV test, hepatitis serologies, baseline LFTs, CBC

— Symptom screen documented

— If CXR normal and asymptomatic → counsel on LTBI, initiate 3HP weekly × 12 weeks

— Schedule monthly follow-up: clinical assessment, pill count, AE review

— Repeat LFTs monthly if risk factors present

— Notify employee health

CCS pearl: If you suspect active TB and the patient is in the ED, order respiratory isolation, induced sputum ×3, AFB smear, NAAT, and CXR simultaneously — don't wait for one to come back before ordering the next. Empirically isolate before confirming.

LTBI is fundamentally an outpatient diagnosis and treatment. Escalation is needed when:

Specialist consults — when to involve:

CCS workflow for "positive IGRA, healthcare worker, asymptomatic":

Transition-of-care risks: Patients moving between providers mid-course frequently fall through cracks; document regimen, doses received, and remaining duration in problem list and discharge summary.

Key Differentials — Same-Category Infectious Mimics

— M. avium complex (MAC), M. kansasii, M. abscessus

— Can cause false-positive TST (cross-reactive PPD antigens); IGRA is more specific to M. tuberculosis

— Clinical: middle-aged women with bronchiectasis (Lady Windermere syndrome), nodular bronchiectatic disease, hot-tub lung

— Treatment: multi-drug, prolonged; do not treat as LTBI

— TST/IGRA may remain positive for life

— Documented adequate prior treatment → do not retreat unless reinfection or reactivation

— Calcified granulomas on CXR without active changes = healed disease

— Vaccination >10 years prior rarely produces TST >10 mm

— Recent BCG (<5 years) can cause modest TST positivity

— IGRA unaffected — use IGRA in BCG-vaccinated patients

— Histoplasmosis (Ohio/Mississippi valleys), coccidioidomycosis (Southwest), blastomycosis

— May show similar calcified granulomas

— Serology and urine antigen testing can differentiate

Board pearl: TST+ / IGRA− in a low-risk patient with BCG vaccination history → most likely BCG cross-reaction, not LTBI. Use IGRA as the tiebreaker; do not treat empirically.

Active pulmonary TB vs LTBI: The critical distinction. Active disease has symptoms (cough >2–3 weeks, hemoptysis, fever, night sweats, weight loss) and/or radiographic findings (apical cavitation, infiltrate, miliary pattern) and/or microbiologic evidence (AFB+ smear, NAAT+, culture+). LTBI has none of these.

Nontuberculous mycobacteria (NTM):

Prior treated TB:

BCG-related TST reactivity:

Endemic mycoses with granulomatous CXR findings:

HIV-related opportunistic pulmonary infection: Pneumocystis, CMV, cryptococcus — exclude in HIV+ patient with respiratory symptoms before attributing to TB

Key Differentials — Non-Infectious Mimics and False Positives

— Sarcoidosis: bilateral hilar lymphadenopathy, upper-lobe predominance, non-caseating granulomas, elevated ACE; can cause apical fibrosis. Distinguish via biopsy showing non-caseating granulomas and negative AFB

— Silicosis: occupational exposure (mining, sandblasting, foundry); upper lobe nodules, eggshell calcifications of hilar nodes. Silicosis dramatically increases TB risk — screen and treat LTBI aggressively

— Pneumoconioses: coal worker's, berylliosis

— Granulomatosis with polyangiitis (GPA): cavitary nodules, but with renal and ENT involvement, ANCA+

— Apical lung cancer (Pancoast tumor) can mimic TB cavitation

— Lymphoma — mediastinal adenopathy

— Always consider PET/CT or biopsy when imaging is atypical

— Severe immunosuppression (advanced HIV with CD4 <100, high-dose steroids, biologics)

— Recent viral infection (measles, varicella, influenza), live virus vaccine within 4–6 weeks

— Recent TB infection within 8–10 week window

— Disseminated/overwhelming TB itself (anergy)

— Malnutrition, age extremes

— Technical: improper TST placement (subcutaneous instead of intradermal), poor IGRA sample handling, prolonged blood transit

— BCG vaccination

— NTM exposure

— Improper measurement (erythema mistaken for induration)

— Booster phenomenon misread as conversion in serial testing — mitigated by two-step testing at baseline

Key distinction: A patient with bilateral hilar adenopathy, elevated ACE, and a positive TST may have sarcoid + LTBI — both can coexist, and starting steroids for sarcoid in untreated LTBI risks reactivation. Treat LTBI first or concurrently.

Granulomatous diseases on CXR (mimicking healed TB):

Malignancy:

Causes of false-negative TST/IGRA (anergy or technical):

Causes of false-positive TST:

Secondary Prevention, Long-Term Plan, and Public Health

— Reactivation risk reduced 60–90% but not zero

— Patient remains TST/IGRA-positive for life — do not retest after treatment; results are uninformative

— Document completion clearly in problem list, medication list, and provide patient with written record

— If new symptoms develop later (cough, fever, weight loss), evaluate for active TB — completion does not preclude future disease

— Generally do not retreat after documented adequate course unless re-infection from new active TB exposure in immunocompromised host

— ID consultation for borderline cases

— In patients starting biologics or transplant, document LTBI treatment status before initiation

— Annual screening for ongoing exposure risk is not routinely needed post-treatment unless new high-risk exposures

— Healthcare workers: per facility risk assessment; baseline two-step TST or IGRA, then only after known exposure (CDC 2019 update — annual screening of low-risk HCWs no longer recommended)

— Correctional/shelter staff: annual or per local protocol

— HIV patients: annual if ongoing risk; otherwise based on exposure

— Dialysis patients: at initiation; repeat with new risk factors

— Active TB is reportable in all 50 states; LTBI reporting varies — know your state

— Public health DOT for high-risk adherence cases

— Contact investigations triggered by new active TB cases

— Symptoms of reactivation to monitor for

— Travel to high-burden countries — re-exposure precautions

— Future immunosuppression — inform any future provider

Step 3 management: A patient completing 3HP for LTBI now starting infliximab → no additional LTBI workup needed; clear documentation suffices. Do not order repeat IGRA — it will be positive.

After completion of LTBI treatment:

Re-exposure:

Pre-immunosuppression follow-through:

Ongoing screening intervals:

Public health partnership:

Counseling at discharge from treatment:

Follow-Up, Monitoring Parameters, and Counseling

— Baseline visit: confirm diagnosis, exclude active TB, baseline labs (LFTs, HIV, hepatitis serologies, pregnancy), shared decision-making, prescribe initial month supply

— Monthly follow-up visits (in person or telehealth):

◦ Symptom check: nausea, anorexia, RUQ pain, dark urine, jaundice, rash, paresthesias, fatigue

◦ Adherence: pill count, refill timing

◦ Side effects review

◦ Reinforce education

◦ Repeat LFTs if baseline abnormal, age >35–50, alcohol, pregnancy, HIV, hep B/C — otherwise symptom-driven

— End-of-treatment visit: confirm completion, document in chart and provide written record, discuss future risk

— Routine monthly LFTs only in high-risk; otherwise symptom-triggered

— Stop drug for ALT >3× ULN + symptoms, or >5× ULN without symptoms

— Recheck LFTs 2 weeks after stopping; consider rechallenge with single agent if cause unclear

— Abstain from or minimize alcohol during treatment

— Avoid acetaminophen excess

— Report symptoms immediately: yellow eyes, dark urine, persistent nausea, RUQ pain, rash, tingling/numbness

— Rifamycins turn body fluids orange — expected and harmless; warn about contact lens staining

— Hormonal contraception failure with rifamycins — backup method required

— Take with or without food (3HP better tolerated with food)

— Importance of completion — partial courses select for resistance and incomplete protection

— Pillboxes, weekly blister packs (especially for 3HP), smartphone reminders, app-based DOT, family/peer support

— Weekly 3HP reduces adherence burden vs daily 9H

CCS pearl: Document monthly visits with symptom checklist, LFT result (when ordered), pill count, and patient education in CCS-style notes; the simulation rewards comprehensive longitudinal management more than aggressive ordering.

Visit cadence during LTBI treatment:

Labs during treatment:

Patient counseling key points:

Adherence aids:

Ethical, Legal, and Patient Safety Considerations

— LTBI treatment is elective preventive therapy in an asymptomatic patient — robust informed consent is essential

— Discuss hepatotoxicity risk, duration, drug interactions, alternative regimens, and option of monitoring without treatment in low-risk individuals

— Document patient's preferences and acceptance/refusal

— Active TB is mandatorily reportable in all 50 states (typically within 24 hours)

— LTBI reporting varies by state — California, New York City, and several others require LTBI reporting; know your jurisdiction

— Reporting is not optional and does not require patient consent (public health exception to confidentiality)

— TB carries cultural and social stigma, especially in immigrant communities

— Counsel using non-stigmatizing language; clarify that LTBI is not contagious

— Protect immigration status concerns — treatment data should not be shared inappropriately

— Healthcare workers, teachers, food handlers in some jurisdictions undergo mandatory screening

— A positive TST/IGRA alone does not preclude work — only active disease requires removal until non-infectious

— Document clearance for work after active TB exclusion

— Minor with positive test requires parental consent for treatment except in emancipated minors or jurisdictions with public health override

— Engage school health, public health

— Patients mid-course who move, lose insurance, or change providers frequently drop out

— Hand-off communication: regimen, doses completed, remaining duration, labs, AEs — all documented in transfer summary

— Public health departments often provide free LTBI treatment for uninsured — refer when needed

— Competent adults may refuse — document discussion, risks of reactivation, plan for monitoring

— For active TB (not LTBI), legal directly observed therapy and even court-ordered isolation apply in nonadherent infectious cases — rare but real

Board pearl: A homeless patient with positive IGRA refuses LTBI treatment. You cannot compel treatment for LTBI (not contagious). Document refusal, offer public health linkage, counsel on symptom monitoring, and respect autonomy.

Informed consent and shared decision-making:

Mandatory reporting:

Confidentiality and stigma:

Occupational health and employment:

Pediatric and parental consent:

Transition-of-care risks (Step 3 favorite):

Refusal of treatment:

High-Yield Associations and Rapid-Fire Facts

— HIV with low CD4: 100× background

— Recent infection (<2 years): 15×

— Silicosis: 30×

— Chronic renal failure/dialysis: 10–25×

— TNF-α inhibitors: 4–8×

— Diabetes: 2–4×

— Smokers: 2–3×

— Underweight (BMI <18.5): 2–3×

— Solid organ transplant: 20–74×

— 5 mm: HIV, recent contact, fibrotic CXR, transplant, immunosuppression

— 10 mm: Recent immigrant, IVDU, congregate setting, lab personnel, high-risk comorbidity, children <4

— 15 mm: Low-risk persons

— 3HP — 12 weekly doses INH + rifapentine

— 4R — 4 months daily rifampin

— 3HR — 3 months daily INH + rifampin

— 9H — 9 months daily INH (with B6 in at-risk)

Key distinction: LTBI is asymptomatic, non-contagious, treated with single or dual drug therapy. Active TB is symptomatic, contagious, requires 4-drug RIPE (rifampin, isoniazid, pyrazinamide, ethambutol) for at least 6 months. Never blur the two.

Risk multipliers for reactivation (memorize relative risk):

TST cutoffs cheat sheet:

Regimen cheat sheet (CDC 2020 preferred):

BCG vs TST vs IGRA: BCG affects TST, not IGRA. NTM can affect both, but more TST.

Window period: 8–10 weeks from exposure to test positivity

Pyridoxine indications with INH: pregnancy, breastfeeding, HIV, diabetes, alcohol, CKD, malnutrition, seizure disorder, age extremes

Rifamycin = body fluids orange + CYP3A4 inducer + OCP failure

CXR before treatment: always. Symptoms before treatment: always reviewed.

HIV testing: offered at every TB workup; co-infection changes management

Two-step TST: baseline for serial-testing populations to detect booster effect

3HP not for: pregnancy, children <2, incompatible ART, suspected drug-resistant exposure

Rifabutin substitutes rifampin in HIV patients on incompatible ART regimens

Board Question Stem Patterns

— 45-year-old with RA about to start adalimumab; CXR clear, no symptoms, IGRA positive. Next step: Start 3HP × 12 weeks or 4R × 4 months before or with biologic initiation. Do not delay RA treatment indefinitely; coordinate.

— 28-year-old immigrant from the Philippines, in US 2 years, TST 12 mm, CXR clear, asymptomatic. Diagnosis: LTBI (≥10 mm cutoff applies). Next step: baseline LFTs, HIV test, then 3HP weekly × 12 weeks.

— Nurse with prior negative TST, now 15 mm after exposure at work. Next step: CXR, HIV test, exclude active TB → if clear, treat LTBI. Report to employee health.

— CD4 350, IGRA+, asymptomatic, CXR clear. Treatment: 3HP (if compatible ART) or 9H + pyridoxine; treat regardless of CD4.

— 26-year-old pregnant, 14 weeks, recent close contact with active pulmonary TB. Next step: TST or IGRA → if positive, treat with INH + pyridoxine daily × 9 months (not 3HP).

— Patient on month 3 of INH develops nausea and RUQ pain, ALT 4× ULN. Next step: Stop INH, recheck LFTs in 2 weeks, evaluate for other causes; consider switching to 4R after recovery.

— TST 12 mm, IGRA negative, born in country with universal BCG. Most likely: BCG cross-reaction. Action: Do not treat (low-risk patient); use IGRA result.

— New ESRD patient starting hemodialysis. Action: Screen with IGRA (preferred over TST); if positive, exclude active TB and treat.

— 3-year-old exposed to TB+ household member, TST negative. Action: Start INH window prophylaxis; repeat TST at 8–10 weeks.

— Woman on combined OCP started on rifampin. Counsel: Use barrier or non-hormonal contraception.

Step 3 management: When the stem includes "asymptomatic, normal CXR, positive screening test, at-risk patient" → the answer is almost always start LTBI treatment with a preferred short-course regimen (3HP or 4R) after baseline labs and HIV testing.

Pattern 1 — Pre-biologic screening:

Pattern 2 — Recent immigrant:

Pattern 3 — Healthcare worker conversion:

Pattern 4 — HIV with positive IGRA:

Pattern 5 — Pregnancy:

Pattern 6 — Hepatotoxicity on INH:

Pattern 7 — Discordant testing in BCG-vaccinated patient:

Pattern 8 — Dialysis screening:

Pattern 9 — Pediatric window prophylaxis:

Pattern 10 — Drug interaction:

One-Line Recap

In asymptomatic at-risk adults with a positive TST or IGRA and a normal CXR, treat latent TB infection with a preferred short-course regimen — 3HP weekly × 12 weeks, 4R daily × 4 months, or 3HR daily × 3 months — after excluding active disease and obtaining baseline LFTs and HIV testing.

Board pearl: The Step 3 essence of LTBI is targeted preventive medicine — match the right test to the right patient, exclude active disease rigorously, choose the shortest effective regimen, monitor adherence and liver safely, and close the loop with documented completion.

Target, then test, then treat: Only screen patients you would treat — recent immigrants, HIV+, immunosuppression candidates (especially pre-TNF-α inhibitor), close contacts, dialysis, silicosis, healthcare workers, congregate settings. TST cutoffs of 5/10/15 mm are risk-stratified; IGRA is preferred in BCG-vaccinated patients and those unlikely to return for reading.

Always exclude active TB before LTBI therapy: symptom screen + CXR mandatory. If symptoms or abnormal CXR — order sputum AFB ×3, NAAT, culture, and isolate. Single-drug therapy for occult active TB selects for resistance — a critical safety pitfall.

Short-course regimens are now first-line (CDC 2020): 3HP (INH + rifapentine weekly × 12) is preferred for most adults and children ≥2 years; 4R (rifampin daily × 4 months) is preferred when INH resistance suspected, intolerance, or hepatotoxicity concerns; 9H reserved for pregnancy, incompatible ART, or when others contraindicated. Add pyridoxine with INH in pregnancy, HIV, diabetes, alcohol, CKD, malnutrition.

Monitor for hepatotoxicity (stop drug for ALT >3× ULN with symptoms or >5× ULN without), counsel on rifamycin drug interactions especially with OCPs and ART (use rifabutin in HIV), document treatment completion in the problem list, do not retest after completion — patients remain TST/IGRA positive lifelong but with 60–90% lower reactivation risk.