Renal & Urinary

Proteinuria: quantification and workup

Clinical Overview and When to Suspect Proteinuria

— Glomerular: increased filtration barrier permeability (diabetic nephropathy, FSGS, membranous, minimal change, IgA, lupus nephritis)

— Tubular: failure to reabsorb filtered low-molecular-weight proteins (ATN, Fanconi, interstitial nephritis, heavy metals)

— Overflow: excess production overwhelms reabsorption (multiple myeloma → Bence Jones, rhabdomyolysis → myoglobin, hemolysis → hemoglobin)

— Post-renal: UTI, bladder tumors, instrumentation (usually low-grade)

— Annual screening in diabetes (T1DM ≥5 yrs after dx; T2DM at dx) and hypertension

— Incidental dipstick proteinuria on routine workup, insurance physical, or employment exam

— Edema, foamy urine, unexplained AKI/CKD, hypertension in young adults

— Systemic disease clues: rash, arthralgias, hemoptysis, weight loss, paraproteinemia symptoms

Board pearl: Step 3 will frequently test the albuminuria-CKD-CV mortality axis: a patient with eGFR 70 and ACR 600 mg/g has worse prognosis than eGFR 45 with ACR 10. Both eGFR and albuminuria are required to stage CKD (KDIGO heat map). Always quantify proteinuria when you discover it—never stop at "trace on dipstick."

Definition: Urinary protein excretion >150 mg/day in adults (>300 mg/day = overt proteinuria; >3.5 g/day = nephrotic range). Albuminuria is the dominant subset and the most clinically actionable marker of glomerular disease.

Why it matters at Step 3: Proteinuria is both a diagnostic clue to glomerular pathology and an independent predictor of CKD progression, cardiovascular mortality, and all-cause mortality—often more so than eGFR alone.

Categories by mechanism:

When to suspect/screen:

Asymptomatic isolated proteinuria in an otherwise healthy adult is usually transient or orthostatic—but must be confirmed and stratified, not dismissed.

Presentation Patterns and Key History

— Periorbital edema worse in morning, dependent edema by evening, anasarca

— Foamy/frothy urine (high surface tension from protein)

— Weight gain, dyspnea from pleural effusion or pulmonary edema

— Hypercoagulable events: renal vein thrombosis (flank pain, hematuria—classic in membranous), DVT/PE

— Infections from urinary IgG loss (especially encapsulated organisms)

— Diabetes duration, retinopathy (parallels nephropathy)

— HTN chronicity and control

— Rash, arthralgias, oral ulcers → SLE

— Hemoptysis → anti-GBM, ANCA vasculitis

— Hepatitis B/C, HIV risk factors → membranous (HBV), MPGN/cryoglobulins (HCV), collapsing FSGS (HIV)

— Bone pain, anemia, hypercalcemia → myeloma

— Recent infection (strep pharyngitis, impetigo, endocarditis) → post-infectious GN

— NSAID, PPI, lithium, pamidronate, anti-VEGF use → drug-induced

Key distinction: Nephrotic = proteinuria >3.5 g/day, hypoalbuminemia <3.0, edema, hyperlipidemia. Nephritic = hematuria with dysmorphic RBCs/RBC casts, HTN, AKI, proteinuria usually <3 g. Overlap (e.g., diffuse proliferative lupus nephritis, MPGN) is common and demands biopsy.

Asymptomatic/incidental: most common scenario—dipstick on routine visit, pre-employment, or pregnancy screening. Usually mild (<1 g/day).

Nephrotic syndrome presentation:

Nephritic overlap (when proteinuria coexists with hematuria, HTN, AKI): suggests proliferative glomerulonephritis—IgA, lupus, post-infectious, ANCA, anti-GBM.

Systemic disease clues to elicit:

Orthostatic (postural) proteinuria: adolescents/young adults <30 yrs, proteinuria present when upright, absent in first morning void. Benign, no treatment.

Transient (functional) proteinuria: fever, vigorous exercise, CHF exacerbation, seizure. Repeat testing after resolution.

Physical Exam Findings and Volume Assessment

— Hypertension: present in most glomerular diseases; severity correlates with prognosis

— Tachycardia if volume-depleted from aggressive diuresis or third-spacing

— Weight gain trend more reliable than single measurement

— Edema: periorbital (morning), pretibial, sacral in bedbound; pitting, symmetric

— JVP often elevated despite intravascular depletion (third-spacing)

— Ascites, pleural effusions (dullness, decreased breath sounds at bases)

— Anasarca in severe nephrotic syndrome

— Malar rash, oral ulcers, alopecia → SLE

— Palpable purpura on lower extremities → IgA vasculitis (HSP), cryoglobulinemia, ANCA

— Livedo reticularis → cholesterol emboli, antiphospholipid syndrome

— Xanthelasma, eruptive xanthomas → hyperlipidemia of nephrotic syndrome

— Muehrcke lines (paired white transverse nail bands) → chronic hypoalbuminemia

— Retinopathy on fundoscopy (diabetic, hypertensive)

— Pulmonary crackles from volume overload

— Pericardial rub in uremia or lupus

— Hepatosplenomegaly → amyloidosis, infiltrative disease

— Flank tenderness → renal vein thrombosis, pyelonephritis

— Synovitis → SLE, vasculitis, cryoglobulinemia

— Peripheral neuropathy → amyloid, vasculitis, diabetes

— Mononeuritis multiplex → vasculitis

Step 3 management: When examining a nephrotic patient, document both intravascular and extravascular volume—they often diverge. Aggressive diuresis without checking orthostatics/BUN trend can precipitate AKI. Daily weights and standing BP are the bedside metrics that drive diuretic titration in CCS.

General/vital signs:

Volume status assessment (critical for management):

Skin and mucosa:

HEENT/cardiopulmonary:

Abdomen:

Musculoskeletal/neuro:

Diagnostic Workup — Initial Labs and Quantification

— Detects primarily albumin via tetrabromophenol blue; +1 ≈ 30 mg/dL, +2 ≈ 100, +3 ≈ 300, +4 ≈ >1000

— Misses: light chains (Bence Jones), myoglobin, hemoglobin—use sulfosalicylic acid (SSA) test if myeloma suspected (positive SSA + negative dipstick = light chains)

— False positives: alkaline urine (pH >8), concentrated urine, gross hematuria, chlorhexidine

— False negatives: dilute urine, non-albumin proteinuria

— Spot urine protein-to-creatinine ratio (UPCR): best initial quantification; ratio in mg/mg ≈ g/day excretion. UPCR 3.5 ≈ 3.5 g/day.

— Spot urine albumin-to-creatinine ratio (UACR): preferred for diabetes/HTN screening and CKD staging

· Normal <30 mg/g; moderately increased (A2) 30–300; severely increased (A3) >300

— 24-hour urine collection: gold standard but cumbersome; validate adequacy with creatinine (men ~20–25 mg/kg/day, women ~15–20)

— BMP (Cr, eGFR, K, HCO3), CBC, albumin, lipid panel, LFTs

— Urinalysis with microscopy: dysmorphic RBCs, RBC casts (GN), fatty casts/oval fat bodies/Maltese crosses (nephrotic), WBC casts (interstitial)

— Hemoglobin A1c if diabetes suspected

Board pearl: A diabetic with retinopathy, slowly rising albuminuria, bland sediment, and gradual eGFR decline does not need a biopsy—the diagnosis is diabetic nephropathy. Biopsy when the picture is atypical: nephrotic-range proteinuria without retinopathy, active sediment, rapid decline, or short DM duration.

Urine dipstick (the screen):

Quantification—the Step 3 pivot:

Confirm persistence: repeat dipstick/UACR ×2–3 over weeks; transient and orthostatic causes will resolve. Split (first-morning vs. daytime) collection confirms orthostatic proteinuria.

Reflex labs:

Diagnostic Workup — Advanced and Confirmatory Studies

— ANA, anti-dsDNA, C3/C4 → SLE (low complements = active lupus nephritis)

— ANCA (PR3, MPO) → granulomatosis with polyangiitis, microscopic polyangiitis

— Anti-GBM → Goodpasture (with hemoptysis + RPGN)

— Anti-PLA2R antibody → primary membranous nephropathy (70% sensitive, highly specific—can avoid biopsy in some cases)

— Hepatitis B surface Ag, Hepatitis C Ab, HIV: HBV→membranous; HCV→MPGN/cryoglobulinemia; HIV→collapsing FSGS

— Cryoglobulins, RF (with HCV)

— ASO, anti-DNase B: post-streptococcal GN

— Complement levels: low in lupus, post-infectious, MPGN, cryoglobulinemia, endocarditis-associated GN

— SPEP + UPEP with immunofixation, serum free light chain ratio (kappa/lambda)

— Bone marrow biopsy if MGUS/myeloma suspected

— Renal ultrasound: kidney size, echogenicity, obstruction, asymmetry (small kidneys → chronic; large → diabetic, HIV, amyloid, infiltrative)

— Renal vein Doppler/CT venogram if RVT suspected in membranous nephropathy

— Indications: nephrotic syndrome in adults (except classic diabetic), unexplained AKI with proteinuria, nephritic syndrome, RPGN, SLE with renal involvement, suspected drug-induced or genetic

— Generally avoid in: classic diabetic nephropathy with retinopathy, single kidney (relative), uncontrolled HTN, bleeding diathesis, active infection

— Light microscopy, immunofluorescence, electron microscopy all needed

Key distinction: In adults with nephrotic syndrome, empiric steroids without biopsy are inappropriate (unlike children, where minimal change is presumed and treated empirically). Adults need tissue diagnosis to avoid mistreating membranous, FSGS, amyloid, or MGRS.

Serologic workup (driven by clinical context):

Paraprotein evaluation (mandatory if >40 yrs with unexplained proteinuria, especially with anemia, bone pain, hypercalcemia, or AKI):

Imaging:

Renal biopsy—the definitive test:

Risk Stratification and Management Logic

— G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15

— A1 <30 mg/g, A2 30–300, A3 >300

— Risk = green (low) → yellow → orange → red (very high). A patient with G2A3 is higher risk than G3aA1.

— <500 mg/day, bland sediment, normal eGFR: outpatient workup, BP control, ACEi/ARB, annual monitoring

— 500 mg–3 g/day: structured workup (serologies, imaging), nephrology referral, aggressive BP and proteinuria targets

— >3 g/day (nephrotic range): prompt nephrology referral, biopsy planning, anticoagulation risk assessment, statin, edema management

— RPGN picture (rising Cr, active sediment, hematuria): urgent admission, empiric pulse steroids while awaiting biopsy in select cases

— eGFR <30, persistent UACR >300, UPCR >1 g/g

— Hereditary kidney disease, unexplained hematuria + proteinuria

— Resistant HTN with kidney disease, refractory electrolyte disturbances

— Rapid eGFR decline >5/year

— BP <130/80 (ACC/AHA, KDIGO) for proteinuric CKD

— Reduce proteinuria by ≥50% from baseline, ideally to <500 mg/day

— eGFR decline up to 30% after starting ACEi/ARB is expected and acceptable if K stable

Step 3 management: For ambulatory proteinuria, structure follow-up at 2–4 weeks after initiating ACEi/ARB to check BMP and BP, then every 3 months to monitor UACR trend. Document the delta in albuminuria as your efficacy metric—stable proteinuria with stable eGFR is a win.

CKD staging (KDIGO heat map): stage by G (eGFR) and A (albuminuria) together:

Triage decisions driven by quantification:

Nephrology referral triggers (Step 3 favorite):

BP and proteinuria targets:

Pharmacotherapy — First-Line Antiproteinuric Therapy

— ACE inhibitors (lisinopril, ramipril, enalapril) or ARBs (losartan, valsartan, irbesartan): titrate to maximum tolerated dose

— Indicated for any albuminuria ≥30 mg/g in diabetics, and proteinuria >500 mg/day in non-diabetics regardless of BP

— Mechanism: efferent arteriolar dilation → reduced intraglomerular pressure → reduced proteinuria

— Do not combine ACEi + ARB (ONTARGET, VA NEPHRON-D: worse AKI/hyperkalemia without benefit)

— Monitor BMP at 1–2 weeks: tolerate up to 30% Cr rise and K ≤5.5

— Indicated in diabetic CKD with UACR ≥30 and increasingly in non-diabetic proteinuric CKD (DAPA-CKD: UACR 200–5000, eGFR 25–75)

— Add to maximally tolerated ACEi/ARB

— Counsel on euglycemic DKA, genitourinary infections, transient eGFR dip

— Hold during acute illness, prolonged fasting, surgery

— FIDELIO-DKD/FIGARO-DKD: reduces CV and renal events in diabetic CKD with albuminuria on ACEi/ARB

— Monitor potassium; avoid if K >5.0 at baseline

Board pearl: The modern "four pillars" of proteinuric CKD therapy = ACEi/ARB + SGLT2 + finerenone + GLP-1 (in DM), plus statin and BP control. Step 3 stems showing a diabetic with eGFR 40, UACR 400 on lisinopril alone want you to add empagliflozin—not increase lisinopril past max dose.

RAAS blockade (cornerstone):

SGLT2 inhibitors (dapagliflozin, empagliflozin):

Nonsteroidal MRA—finerenone:

GLP-1 receptor agonists (semaglutide): FLOW trial—renal protection in diabetic CKD; favored in obesity/CV disease

Statins: indicated for ASCVD risk reduction in CKD (most patients ≥50 with CKD qualify regardless of LDL per KDIGO)

Loop diuretics (furosemide, torsemide): for edema/volume overload; high doses often needed in nephrotic syndrome due to albumin binding and tubular resistance—consider IV or adding thiazide for sequential blockade

Disease-Specific and Immunosuppressive Therapy

— Prednisone 1 mg/kg/day (max 80 mg) × 4–16 weeks, then taper

— Steroid-dependent/resistant: cyclophosphamide, calcineurin inhibitors, rituximab

— Primary: prednisone ± calcineurin inhibitor (tacrolimus, cyclosporine)

— Secondary (obesity, HIV, reflux): treat underlying cause + RAAS blockade; no immunosuppression

— Collapsing variant (HIV-associated): ART is first-line

— Risk-stratify by proteinuria, eGFR, anti-PLA2R titer

— Low risk: conservative (RAAS, statin) for 6 months

— Moderate/high risk: rituximab (now first-line per KDIGO 2021) or cyclophosphamide + steroids (modified Ponticelli)

— RAAS blockade + SGLT2i first; targeted-release budesonide (Nefecon) for persistent proteinuria

— Systemic steroids: selective use given TESTING trial toxicity signal

CCS pearl: When ordering immunosuppression on CCS, also order PJP prophylaxis (TMP-SMX), PPI, calcium/vitamin D + bisphosphonate for prolonged steroids, hepatitis B/C/HIV/TB screening before biologics, and update pneumococcal, influenza, shingles (non-live) vaccines. Missing prophylaxis loses points.

Diabetic nephropathy: RAAS blockade + SGLT2i + finerenone + glycemic control (A1c ~7%, individualized) + BP control. Biopsy not routinely required.

Minimal change disease (pediatric default, adult ~10%):

FSGS:

Membranous nephropathy:

IgA nephropathy:

Lupus nephritis (Class III/IV): induction with mycophenolate or low-dose cyclophosphamide + steroids ± belimumab or voclosporin; maintenance with MMF or azathioprine

ANCA vasculitis: rituximab or cyclophosphamide + steroids; plasma exchange for severe pulmonary-renal

Anti-GBM: plasmapheresis + cyclophosphamide + steroids, urgent

Amyloidosis: treat underlying clone (chemotherapy for AL; colchicine/anti-IL-1 for AA)

Special Populations — Elderly and Renal/Hepatic Impairment

— Sarcopenia lowers creatinine generation → eGFR may overestimate function; use cystatin C or measured CrCl when decisions hinge on precise GFR

— Higher prevalence of membranous, amyloidosis, paraprotein-related (MGRS), and pauci-immune GN—always send SPEP/UPEP/free light chains in adults >50 with new nephrotic syndrome

— Polypharmacy: review NSAIDs, PPIs (interstitial nephritis), aminoglycosides, contrast exposure

— Orthostatic hypotension risk with combined ACEi + diuretic + alpha-blocker—start low, go slow, check standing BP

— Goal BP <130/80 still applies but individualize; SPRINT excluded nursing-home residents

— ACEi/ARB: continue unless symptomatic hypotension, K >5.5 despite optimization, or AKI; STOP-ACEi trial showed no benefit to stopping in advanced CKD

— SGLT2i: continue down to eGFR ~20 (start ≥20); do not initiate in dialysis

— Avoid metformin if eGFR <30; reduce dose 30–45

— Adjust gabapentin, allopurinol, digoxin, LMWH, DOACs (apixaban most CKD-friendly)

— Hyperkalemia management: dietary counseling, loop diuretic, patiromer/sodium zirconium to preserve RAAS blockade

— Cirrhosis with proteinuria: consider HCV-associated MPGN, IgA nephropathy of cirrhosis, hepatorenal physiology

— Avoid hepatically cleared agents; spironolactone is mainstay for cirrhotic edema but watch K

— Albumin infusion for SBP, large-volume paracentesis, HRS—not for routine nephrotic edema

Step 3 management: In an 82-year-old with new nephrotic syndrome, anemia, and back pain, order SPEP/UPEP/SFLC and skeletal survey before ordering a biopsy—you may diagnose myeloma noninvasively and change the entire plan.

Elderly:

Advanced CKD (eGFR <30):

Hepatic impairment:

Dual organ disease: HBV-membranous → treat HBV with entecavir/tenofovir (often resolves nephropathy)

Special Populations — Pregnancy and Pediatrics

— Physiologic proteinuria up to 300 mg/24 hr is normal; >300 mg/day is abnormal

— Preeclampsia: new HTN after 20 weeks + proteinuria ≥300 mg/24h (or UPCR ≥0.3) OR end-organ dysfunction. Severe features include proteinuria-independent criteria.

— Chronic kidney disease in pregnancy: increased risk of preeclampsia, preterm birth, IUGR; preconception counseling is essential

— ACEi/ARB/SGLT2i/MRA contraindicated: teratogenic (renal dysgenesis, oligohydramnios)—switch to labetalol, nifedipine, methyldopa, hydralazine before conception

— Aspirin 81 mg from 12 weeks for preeclampsia prevention in high-risk (prior preeclampsia, CKD, chronic HTN, DM, SLE, APLS)

— Lupus nephritis: aim for remission ≥6 months before conception; hydroxychloroquine continued; azathioprine and tacrolimus pregnancy-compatible; MMF and cyclophosphamide teratogenic

— Nephrotic syndrome in children: 80–90% minimal change disease—empiric prednisone 60 mg/m²/day without biopsy

— Biopsy if: <1 yr or >12 yrs, gross hematuria, HTN, low C3, AKI, steroid-resistant

— Orthostatic proteinuria: most common cause of isolated proteinuria in adolescents; confirm with split urine (absent in first morning specimen)—benign, reassure, no treatment

— HSP/IgA vasculitis: palpable purpura, abdominal pain, arthritis, hematuria/proteinuria—usually self-limited; nephritis may require steroids

— Post-streptococcal GN: 1–3 weeks after pharyngitis, 3–6 weeks after impetigo; supportive care

Board pearl: A 16-year-old athlete with +1 dipstick proteinuria on sports physical, normal exam, normal BP—get a first-morning urine. Negative = orthostatic, reassure. No biopsy, no nephrology referral.

Pregnancy:

Pediatrics:

Adolescent screening: routine dipstick screening not recommended in asymptomatic kids (AAP/USPSTF)

Complications and Adverse Outcomes

— Thromboembolism: loss of antithrombin III, protein S, plasminogen → hypercoagulable state. Risk highest in membranous nephropathy (up to 30%) and with albumin <2.5 g/dL. Renal vein thrombosis, DVT, PE.

· Prophylactic anticoagulation considered when albumin <2.0–2.5 in membranous (warfarin preferred historically; DOACs increasingly used)

— Infection: urinary loss of IgG and complement factor B → susceptibility to encapsulated organisms (pneumococcus → spontaneous bacterial peritonitis in children), cellulitis. Pneumococcal vaccination indicated.

— Hyperlipidemia: hepatic compensatory synthesis; statin therapy for ASCVD risk

— AKI: from aggressive diuresis, NSAIDs, contrast, sepsis, or RVT

— Protein-energy malnutrition and muscle wasting in chronic cases

— Vitamin D deficiency and secondary hyperparathyroidism from urinary loss of vitamin D-binding protein

— Iron-resistant anemia from transferrin loss

— Anemia (EPO deficiency, iron deficiency from blood loss)

— CKD-MBD: hyperphosphatemia, low calcitriol, secondary hyperparathyroidism, vascular calcification

— Metabolic acidosis → bone demineralization, accelerated CKD; treat with sodium bicarbonate if HCO3 <22

— Hyperkalemia (worsened by ACEi/ARB/MRA)

— Cardiovascular: leading cause of death in CKD; albuminuria is independent risk factor

— ESKD requiring renal replacement therapy

— Steroid toxicity (DM, osteoporosis, infection, AVN, cataracts)

— Cyclophosphamide: cytopenias, infertility, hemorrhagic cystitis, malignancy

— Calcineurin inhibitor nephrotoxicity (paradoxical worsening)

Key distinction: A nephrotic patient with sudden flank pain, gross hematuria, and worsening proteinuria has renal vein thrombosis until proven otherwise—get renal vein Doppler or CT/MR venogram. Anticoagulate immediately.

Complications of nephrotic syndrome:

Complications of progressive proteinuria/CKD:

Iatrogenic:

When to Escalate Care

— Rapidly progressive GN: doubling of creatinine over days–weeks with active sediment

— Severe AKI (KDIGO stage 2–3) with proteinuria

— Symptomatic hyperkalemia (K >6.0 or ECG changes)

— Refractory hypertensive emergency

— Anasarca with respiratory compromise from pleural effusions or pulmonary edema

— Severe hypoalbuminemia <1.5 with hemodynamic instability

— Suspected RVT, PE, or other thromboembolic complication

— Pulmonary-renal syndrome (hemoptysis + GN) → anti-GBM or ANCA—ICU

— Need for urgent biopsy with anticoagulation reversal

— Diffuse alveolar hemorrhage

— Need for emergent plasmapheresis (anti-GBM, severe ANCA, TTP-mimicking syndromes)

— Need for emergent dialysis (refractory hyperkalemia, acidosis, volume overload, uremic complications—AEIOU)

— Hemodynamic instability from sepsis on immunosuppression

— Nephrology: as outlined—any nephrotic syndrome, RPGN, unexplained CKD, biopsy planning

— Rheumatology: SLE, ANCA vasculitis co-management

— Hematology/Oncology: paraprotein-related, AL amyloid, lymphoma-associated MN

— Interventional radiology: for biopsy, RVT thrombolysis

— Transplant nephrology: when eGFR <20 and progression expected

CCS pearl: For RPGN on CCS, the high-yield order set is: admit, IV pulse methylprednisolone 500–1000 mg daily ×3, send ANCA/anti-GBM/ANA/complements, urgent renal biopsy, plasmapheresis if anti-GBM or severe ANCA, PJP prophylaxis, GI/bone prophylaxis, type and screen for biopsy, hold ACEi/ARB during AKI. Time-sensitivity is graded.

Inpatient admission indicators:

ICU triggers:

Specialty consults:

Dialysis access planning: refer for AV fistula creation when eGFR ~15–20 and progressive; permanent catheter is last resort

Key Differentials — Glomerular Causes by Pattern

— Minimal change: children > adults; abrupt-onset edema; normal BP/Cr; bland sediment; responds to steroids; associations: NSAIDs, Hodgkin lymphoma

— FSGS: most common primary nephrotic GN in US adults, especially Black patients (APOL1); secondary causes: obesity, HIV, heroin, reflux, reduced nephron mass

— Membranous nephropathy: most common in middle-aged/older White adults; anti-PLA2R in 70% of primary; secondary: malignancy (especially solid tumors >60 yrs), HBV, SLE class V, drugs (NSAIDs, gold, penicillamine), syphilis

— Diabetic nephropathy: gradual albuminuria progression over years; nodular Kimmelstiel-Wilson lesions; parallels retinopathy

— Amyloidosis (AL, AA): heavy proteinuria with relatively preserved kidneys on US; apple-green birefringence with Congo red

— Light chain deposition disease/MGRS: paraprotein-driven

— IgA nephropathy: most common GN worldwide; synpharyngitic hematuria (within days of URI, vs. 1–3 weeks for PSGN); mesangial IgA deposits

— Post-infectious GN: low C3, normal C4; hump-shaped subepithelial deposits; supportive treatment

— MPGN: low C3 and C4; immune complex (HCV, cryoglobulins, SLE) or complement-mediated (C3 glomerulopathy, dense deposit disease)

— Lupus nephritis: ISN/RPS classes I–VI; class III/IV proliferative needs aggressive immunosuppression; class V membranous

— ANCA-associated: pauci-immune crescentic GN; PR3 (GPA) or MPO (MPA/EGPA)

— Anti-GBM: linear IgG on IF; rapid course; pulmonary-renal syndrome (Goodpasture)

Key distinction: Low complements narrow nephritic differential to lupus, post-infectious, MPGN, cryoglobulinemia, endocarditis-associated, atheroembolic, shunt nephritis. Normal complements → IgA, ANCA, anti-GBM, HSP. This single lab dramatically narrows the workup.

Nephrotic syndrome differential:

Nephritic syndrome differential:

Key Differentials — Non-Glomerular Causes

— Acute interstitial nephritis: drugs (NSAIDs, PPIs, beta-lactams, sulfonamides, allopurinol, checkpoint inhibitors); classic triad of rash, fever, eosinophilia present in only ~10%; eosinophiluria not specific

— Fanconi syndrome: glycosuria with normal glucose, aminoaciduria, phosphaturia, RTA type 2; causes include myeloma, tenofovir, ifosfamide, cisplatin, Wilson disease, heavy metals

— Chronic interstitial nephritis: lithium, lead, aristolochic acid, analgesic nephropathy, sarcoid, Sjögren

— ATN: ischemic, nephrotoxic; muddy brown casts; FENa >2%

— Multiple myeloma/light chain disease: Bence Jones proteins; dipstick negative but SSA positive; SPEP/UPEP/SFLC diagnostic; cast nephropathy on biopsy

— Rhabdomyolysis: myoglobinuria; dipstick positive for blood, no RBCs on microscopy; CK markedly elevated

— Intravascular hemolysis: hemoglobinuria; haptoglobin low

— Lower UTI, prostatitis, bladder/upper tract malignancy, instrumentation, stones with infection

— Orthostatic (adolescents/young adults, <1 g/day, absent in first morning void)

— Transient: fever, vigorous exercise, dehydration, seizure, CHF exacerbation

— Pregnancy physiologic proteinuria

— Hypertensive nephrosclerosis (modest proteinuria, often <1 g)

— Atheroembolic disease (livedo, eosinophilia, low complement)

— Thrombotic microangiopathy (TTP, HUS, malignant HTN, scleroderma renal crisis)

Board pearl: An older patient with dipstick-negative urine but SSA-positive, anemia, hypercalcemia, and AKI has myeloma cast nephropathy—dipsticks miss light chains entirely. Order SPEP/UPEP/SFLC; do not wait for biopsy if hematology workup is positive.

Tubular proteinuria (low-molecular-weight proteins; usually <2 g/day; bland sediment or WBCs/eosinophils):

Overflow proteinuria:

Post-renal:

Benign/functional:

Vascular:

Secondary Prevention and Long-Term Plan

— BP target <130/80 with ACEi or ARB as first-line antihypertensive

— Albuminuria reduction: target ≥50% reduction or UACR <300; titrate ACEi/ARB to max tolerated dose

— SGLT2i for any proteinuric CKD with eGFR ≥20 (diabetic or not)

— Glycemic control A1c ~7% in DM, individualized

— Statin for ASCVD risk reduction (most CKD ≥50 qualify)

— Sodium restriction <2 g/day enhances RAAS blockade and BP control

— Protein: moderate (0.6–0.8 g/kg/day) in non-dialysis CKD; not severely restricted

— Smoking cessation: independent driver of proteinuria progression and CV risk

— Weight loss in obesity-related FSGS and metabolic syndrome

— Avoid nephrotoxins: NSAIDs, IV contrast when possible, aminoglycosides, herbal supplements (aristolochic acid)

— Pneumococcal (PCV20 or PCV15→PPSV23)

— Annual influenza

— Hepatitis B series (higher dose in CKD)

— Recombinant zoster (Shingrix) ≥50 yrs or immunocompromised

— COVID-19 per current schedule

— Avoid live vaccines on immunosuppression (MMR, varicella, yellow fever, oral typhoid, intranasal flu)

Step 3 management: Discharge planning for a patient with new nephrotic syndrome: ACEi/ARB, statin, loop diuretic, salt restriction, anticoagulation risk assessment, pneumococcal vaccine, nephrology follow-up within 1–2 weeks, BMP and UPCR at follow-up.

Pillars of conservative CKD management (all proteinuric patients):

Vaccinations (especially before immunosuppression):

Bone and metabolic: vitamin D repletion, phosphate binders if hyperphosphatemic; bisphosphonate + calcium/vit D with chronic steroids

Anemia: iron repletion (ferritin >100, TSAT >20%), ESA if Hb <10 after iron repletion

Cardiovascular prevention: aspirin per usual indications; statin per KDIGO; lifestyle counseling

Advance care planning: introduce early in advancing CKD; discuss dialysis modalities, transplant candidacy, conservative care

Follow-Up, Monitoring, and Counseling

— Mild proteinuria (<500 mg) on ACEi/ARB: BMP/UACR at 2–4 weeks after initiation/titration, then every 3–6 months

— Moderate (500 mg–3 g): every 1–3 months until stable, then every 3–6 months

— Nephrotic-range or active disease: every 2–4 weeks initially with nephrology co-management

— Post-biopsy: confirm hemostasis at 24 hr, then disease-specific cadence

— On immunosuppression: monthly CBC/BMP/LFTs initially, drug levels for tacrolimus/cyclosporine, screen for infection

— UACR or UPCR trend (efficacy)

— eGFR/Cr trend (safety and progression)

— Potassium (RAAS/MRA toxicity)

— BP (home measurements logged)

— Weight (volume status)

— Albumin, lipids in nephrotic patients

— Specific serologies: anti-PLA2R titer in MN (correlates with activity), C3/C4 and dsDNA in lupus, ANCA titers in vasculitis

— Home BP monitoring with goal logbook

— Sodium restriction with practical tips (label reading, restaurant strategies)

— Daily weights when on diuretics; sick-day rules

— Sick-day rules: hold ACEi/ARB, SGLT2i, MRA, NSAIDs, metformin during acute illness with vomiting/diarrhea/poor PO intake to prevent AKI and DKA

— Recognize signs of worsening (increasing edema, decreased urine output, dyspnea)

— Medication adherence, especially with chronic immunosuppression

CCS pearl: When discharging a CKD patient on a new SGLT2 inhibitor, explicitly counsel on sick-day rules and euglycemic DKA. Document patient understanding. Missing this counseling step is a frequent CCS deduction.

Outpatient cadence:

Monitoring parameters:

Patient counseling/self-management:

Vocational/lifestyle: most patients can continue work; counsel on heavy NSAID use, contrast exposures, hydration in athletes

Transplant referral: at eGFR <20 with progressive disease; living-donor education improves outcomes

Ethical, Legal, and Patient Safety Considerations

— Discuss risks: bleeding (1–2% requiring transfusion, <0.1% nephrectomy), pain, AV fistula, infection, perinephric hematoma

— Document benefit: tissue diagnosis guides therapy with major prognostic and therapeutic implications

— In Jehovah's Witness patients, document specific blood-product preferences in advance; have a hematologist/anesthesia plan for hemostasis

— Adolescents: assent + parental consent; emancipated minors may consent independently

— APOL1 risk variants in patients of African ancestry inform FSGS/HIVAN risk and live-donor evaluation

— Counsel on implications for family members and insurance/employment (GINA protects most but not life or disability insurance)

— Hospital discharge on new immunosuppression: ensure PJP prophylaxis, vaccinations done before discharge, follow-up labs scheduled, medication reconciliation

— Pregnancy planning: women on ACEi/ARB/MMF must be counseled and switched before conception; document contraception discussion

— Patients leaving against medical advice with active GN: document capacity assessment, risk discussion, follow-up plan, and offer of return

— Medication safety: NSAID counseling at every visit—huge avoidable harm in CKD

— Contrast exposure: prophylactic IV isotonic fluids for high-risk procedures; hold metformin/SGLT2i; gadolinium type matters (group I avoided in advanced CKD due to NSF)

— Hold ACEi/ARB and diuretics for surgery per protocol; coordinate with surgical team

Board pearl: A 28-year-old woman with lupus nephritis on mycophenolate asks about pregnancy. The correct action: stop MMF, switch to azathioprine or tacrolimus, achieve ≥6 months of remission, continue hydroxychloroquine, prescribe low-dose aspirin from 12 weeks, then plan conception.

Informed consent for renal biopsy:

Genetic testing considerations:

Transitions of care—high-risk handoffs:

Patient safety:

Mandatory reporting and public health: TB testing before biologics; report active TB and certain communicable diseases per state law

Resource stewardship: avoid unnecessary repeat 24-hr urines when spot UPCR suffices; avoid routine biopsy in classic diabetic nephropathy

Living donor evaluation: potential donors with persistent proteinuria are typically excluded from donation; counsel transparently and document

High-Yield Associations and Rapid-Fire Clinical Facts

Key distinction: The five "low-complement nephritides" recur in stems: lupus, post-infectious, MPGN, cryoglobulinemic, endocarditis/shunt-associated GN. Memorize this pentad—it appears repeatedly.

Membranous + malignancy in adults >60: screen with age-appropriate cancer screening (colonoscopy, mammography, low-dose CT chest if eligible); anti-PLA2R negative MN raises secondary suspicion.

Minimal change + Hodgkin lymphoma: classic paraneoplastic association.

Membranous + HBV (kids), MPGN/cryoglobulinemia + HCV, collapsing FSGS + HIV: viral-renal associations.

APOL1 high-risk variants: FSGS, HIVAN, hypertensive nephrosclerosis in patients of African ancestry; relevant for transplant.

Anti-PLA2R: primary membranous; titer tracks activity and predicts relapse.

Anti-PLA2R negative + thrombospondin type-1 domain-containing 7A (THSD7A): ~3% of MN, more malignancy-associated.

C3 glomerulopathy: persistent low C3 with normal C4; check C3 nephritic factor and complement regulatory gene panels.

IgA nephropathy + palpable purpura + abdominal pain + arthritis = IgA vasculitis (HSP).

Diabetic nephropathy without retinopathy → reconsider diagnosis; non-diabetic kidney disease in 30%.

Nephrotic syndrome + renal vein thrombosis → membranous nephropathy.

Pulmonary-renal syndrome differential: anti-GBM, GPA, MPA, EGPA, SLE, cryoglobulinemia.

Eosinophiluria: not specific—seen in AIN, atheroembolic, UTI, prostatitis.

Maltese cross under polarized light: lipiduria = nephrotic-range proteinuria.

Onion-skin arterioles: malignant HTN, scleroderma renal crisis.

Bilateral nephromegaly with proteinuria: amyloidosis, HIVAN, diabetic, infiltrative.

Foamy urine + edema = nephrotic until proven otherwise.

Hematuria + proteinuria together = always glomerular until proven otherwise.

Dipstick negative + SSA positive = light chains (myeloma).

Synpharyngitic hematuria = IgA; post-pharyngitic (1–3 weeks) = PSGN.

Edema worse in morning periorbitally = renal (vs. cardiac/dependent which worsens by evening).

Board Question Stem Patterns

Board pearl: When a stem gives you both eGFR and UACR, the albuminuria column often drives the answer—don't fixate on eGFR alone.

The diabetic with new albuminuria stem: 58 yo with T2DM, A1c 8.2, BP 138/86, UACR 65, eGFR 72. Diagnosis: early diabetic nephropathy. Best next step: start ACEi (or ARB), optimize glycemic control, add SGLT2i if eGFR allows. Wrong answer: order biopsy.

The PLA2R stem: 55 yo White man, lower-extremity edema, UPCR 6.0, albumin 2.4, normal eGFR, anti-PLA2R positive, age-appropriate cancer screen negative. Diagnosis: primary membranous nephropathy. Best next step: risk-stratify; for moderate-high risk, rituximab is first-line per KDIGO 2021.

The orthostatic adolescent stem: 17 yo athlete, +1 dipstick on sports physical, asymptomatic. Best next step: first-morning urine UPCR—not biopsy, not nephrology.

The myeloma masquerade stem: 68 yo with fatigue, back pain, Cr 2.8, anemia, hypercalcemia, dipstick trace protein but SSA strongly positive. Best next step: SPEP/UPEP/serum free light chains, then skeletal survey/MRI, hematology referral.

The RPGN stem: 38 yo with hemoptysis, hematuria, Cr rising from 1.0 to 4.2 in 2 weeks, +ANCA. Best next step: admit, pulse steroids, urgent biopsy, plan for rituximab/cyclophosphamide, consider plasmapheresis for severe pulmonary involvement.

The renal vein thrombosis stem: known membranous patient with acute flank pain, gross hematuria, worsening proteinuria. Best next step: renal vein imaging + anticoagulation.

The pregnant patient with chronic HTN stem: 32 yo on lisinopril planning pregnancy. Best next step: switch to labetalol or nifedipine pre-conception; add aspirin 81 mg at 12 weeks if high-risk.

The IgA stem: 24 yo with gross hematuria within 24–48 hr of URI, mild proteinuria. Diagnosis: IgA nephropathy. Management: RAAS blockade ± SGLT2i; biopsy if proteinuria persists or eGFR declines.

The post-strep stem: 8 yo with cola-colored urine 2 weeks after pharyngitis, low C3, normal C4. Management: supportive—BP control, salt/fluid restriction, treat residual infection.

The CKD heatmap stem: which patient is highest risk—G1A3 vs. G3aA1? G1A3 (severe albuminuria trumps modest eGFR drop).

One-Line Recap

Proteinuria is the single most actionable biomarker in nephrology: quantify it accurately, classify it mechanistically, treat it aggressively with RAAS blockade plus SGLT2 inhibitors plus disease-specific therapy, and follow it relentlessly as both your diagnostic compass and your therapeutic scorecard.

Quantify first: spot UACR or UPCR replaces 24-hr collection in most settings; confirm persistence with repeat testing; remember dipsticks miss light chains—use SSA when myeloma is suspected.

Classify by pattern: nephrotic (>3.5 g, hypoalbuminemia, edema, hyperlipidemia) vs. nephritic (hematuria, RBC casts, HTN, AKI) vs. tubular/overflow/orthostatic/transient—each carries a distinct workup and differential.

Stage with both axes: KDIGO heatmap combines eGFR (G1–G5) and albuminuria (A1–A3); albuminuria often drives prognosis more than eGFR; G1A3 outranks G3aA1 for adverse outcomes.

Treat the four pillars: ACEi/ARB (titrate to max, accept 30% Cr rise and K ≤5.5) + SGLT2i (diabetic and non-diabetic CKD with eGFR ≥20) + finerenone (diabetic CKD with albuminuria) + GLP-1 RA (in diabetes); add statin, BP <130/80, sodium <2 g/day; biopsy adults with unexplained nephrotic syndrome or RPGN before empiric immunosuppression.

Don't miss the red flags: RPGN demands urgent admission and pulse steroids; renal vein thrombosis in membranous; myeloma in older adults with dipstick-negative but SSA-positive proteinuria; pregnancy contraindicates ACEi/ARB/SGLT2i/MMF—switch preconception; sick-day rules prevent iatrogenic AKI.

Follow forever: UACR trend is your scoreboard—target ≥50% reduction or <300 mg/g; nephrology referral when eGFR <30, UACR persistently >300, or unexplained progression.