How should I initially evaluate and manage an adult patient presenting with nephrotic syndrome of unknown cause?

Initial Evaluation and Management of Adult Nephrotic Syndrome

Quantify proteinuria immediately using a spot urine protein-to-creatinine ratio (PCR >300–350 mg/mmol or ≥3.5 g/day confirms nephrotic-range proteinuria) and refer urgently to nephrology within 2 weeks while initiating supportive care with sodium restriction, loop diuretics, and maximal RAS blockade. 1, 2

Diagnostic Confirmation and Initial Workup

Confirm the diagnosis by documenting:

• Nephrotic-range proteinuria: PCR ≥3500 mg/g (≥350 mg/mmol) or 24-hour urine protein ≥3.5 g/day 1, 3
• Hypoalbuminemia: Serum albumin <3.0 g/dL 1
• Edema: Typically periorbital (morning) or dependent pitting edema (later in day) 2
• Hyperlipidemia: Check lipid panel for elevated cholesterol and triglycerides 3

Exclude secondary causes immediately before considering immunosuppression 3:

• Diabetes mellitus (most common secondary cause in adults—check HbA1c, fasting glucose) 1
• Systemic lupus erythematosus (ANA, anti-dsDNA, complement levels) 3
• Infections: HIV, hepatitis B/C, syphilis serology 3
• Malignancy: Age-appropriate cancer screening, particularly hematologic malignancies 4
• Medications: NSAIDs, lithium, interferon, bisphosphonates 1
• Amyloidosis: Consider in patients >50 years with multisystem symptoms 5

Kidney Biopsy Decision

Proceed directly to kidney biopsy in all adults to establish the specific glomerular diagnosis, as this determines whether immunosuppression is appropriate 3, 2.

The single exception: Defer biopsy if serum anti-phospholipase A2 receptor (PLA2R) antibodies are positive, which is diagnostic of primary membranous nephropathy 4.

Critical pitfall: Failing to distinguish primary from secondary causes has life-threatening implications—immunosuppression should never be used in secondary FSGS or diabetic nephropathy 1. In diabetic patients, biopsy is mandatory unless the presentation is classic (diabetes >5 years, diabetic retinopathy present, gradual proteinuria onset, no active sediment) 1.

Universal Supportive Care (Start Immediately)

Proteinuria and Blood Pressure Control

• Initiate ACE inhibitor or ARB at maximally tolerated doses in all patients with proteinuria >50 mg/mmol 3
• Target systolic blood pressure <120 mmHg using standardized office measurement 3
• This must be optimized before any immunosuppression is considered 1

Edema Management

• Restrict dietary sodium to <2 g/day (critical for reducing edema and proteinuria) 3
• Use loop diuretics as first-line: Furosemide 0.5–2 mg/kg per dose, up to 6 doses daily (maximum 10 mg/kg/day) 1
• Avoid routine prophylactic albumin infusions—reserve only for clinical hypovolemia (hypotension, tachycardia), not based on serum albumin levels 1, 3

Cardiovascular and Thrombotic Risk

• Start statin therapy for persistent dyslipidemia (target LDL <100 mg/dL) 1
• Consider anticoagulation when serum albumin <2.0 g/dL, especially with additional risk factors (immobility, prior thrombosis, membranous nephropathy) 1, 4
• Membranous nephropathy carries the highest thrombotic risk (29% renal vein thrombosis, 17–28% pulmonary embolism) 1

SGLT2 Inhibitor for CKD Protection

• Add dapagliflozin or empagliflozin if eGFR ≥20 mL/min/1.73 m² and urine albumin-to-creatinine ratio ≥200 mg/g, on top of maximal RAS blockade 1
• Monitor for initial eGFR dip of 3–5 mL/min/1.73 m² in first 4 weeks (reversible, not an indication to stop) 1
• Hold during acute illness with nausea/vomiting/diarrhea to prevent ketoacidosis 1

Infection Prevention

• Administer pneumococcal and influenza vaccines (immunoglobulin loss increases infection risk) 3
• Consider trimethoprim-sulfamethoxazole prophylaxis if high-dose immunosuppression is planned 3
• Screen for latent tuberculosis and hepatitis B/C before starting any immunosuppressive therapy 1

Biopsy-Specific Immunosuppressive Therapy

Focal Segmental Glomerulosclerosis (FSGS)

First-line therapy (only after confirming primary/idiopathic FSGS and excluding genetic/secondary causes) 1, 3:

• Prednisone 1 mg/kg/day (maximum 80 mg) or alternate-day 2 mg/kg (maximum 120 mg) 1, 6
• Continue for minimum 4 weeks, extending up to 16 weeks or until complete remission 1, 3
• After remission, taper slowly over 6 months to reduce relapse risk 1, 3

Steroid-resistant FSGS (no response after 16 weeks):

• Cyclosporine 3–5 mg/kg/day (target trough 125–175 ng/mL) for at least 6 months—expect 70% response with 50% relapse rate 1
• Tacrolimus provides comparable efficacy to cyclosporine 1

Critical consideration: Patients with proteinuria >3.8 g/day have 35% risk of ESRD within 2 years, and those with persistent nephrotic syndrome have >50% risk of ESRD within 5–10 years if untreated 1. Remission of proteinuria is the most significant predictor of renal survival 1.

Membranous Nephropathy

Observe with maximal supportive care for 6 months if proteinuria >4 g/day but renal function remains stable—defer immunosuppression during this period 1, 3.

Initiate immunosuppression if:

• Proteinuria persists >4 g/day and remains >50% of baseline after 6 months of conservative therapy, OR
• Severe/disabling symptoms are present, OR
• Serum creatinine rises ≥30% within 6–12 months while eGFR stays >25–30 mL/min/1.73 m² 1, 3

Recommended regimen:

• Alternating monthly cycles of oral/IV corticosteroids combined with oral alkylating agent (cyclophosphamide or chlorambucil) for total of 6 months 1
• Calcineurin inhibitors (cyclosporine or tacrolimus) are acceptable alternatives 1

Minimal Change Disease

Prednisone 1 mg/kg/day (maximum 80 mg) or alternate-day 2 mg/kg (maximum 120 mg) 3, 6

• Consider cyclosporine as alternative if contraindications to high-dose corticosteroids exist 1

Monitoring and Follow-Up

• Assess proteinuria regularly using spot PCR or 24-hour collections; complete remission = proteinuria <200 mg/g (<20 mg/mmol) 1
• Schedule visits every 2–4 weeks during first 2–4 months of therapy, then every 3–6 months thereafter 1
• Monitor therapeutic drug levels when using calcineurin inhibitors to maintain target trough and minimize nephrotoxicity 1
• Calculate eGFR every 3 months to detect progressive CKD 7

Nephrology Referral Thresholds

Urgent referral (within 2 weeks) for all adults with confirmed nephrotic syndrome 2.

Refer to transplant center early if eGFR <30 mL/min/1.73 m² or proteinuria >3.8 g/day (high ESRD risk) 7, 1.