How should I evaluate and manage an adult with new hematuria, proteinuria, impaired renal function, and systemic symptoms suggestive of nephritis?

Evaluation and Management of Adult Nephritis with Hematuria, Proteinuria, and Impaired Renal Function

Obtain an urgent kidney biopsy to establish the specific diagnosis, as clinical and laboratory findings alone cannot reliably distinguish between different forms of glomerulonephritis, and treatment differs substantially based on the underlying etiology. 1, 2, 3

Immediate Diagnostic Confirmation

Verify True Glomerular Disease

• Confirm microscopic hematuria with ≥3 red blood cells per high-power field (RBC/HPF) on properly collected urine specimens, as dipstick testing has only 65–99% specificity and may yield false positives. 4
• Examine urinary sediment for dysmorphic RBCs (>80% indicates glomerular origin) and red cell casts (pathognomonic for glomerulonephritis), which are essential for distinguishing glomerular from non-glomerular bleeding. 4, 5, 6, 7
• Quantify proteinuria using spot urine protein-to-creatinine ratio; values >0.5 g/g strongly suggest renal parenchymal disease, and values >1.0 g/g warrant immediate nephrology referral. 4, 5
• Tea-colored or cola-colored urine is a visual indicator of glomerular bleeding and should heighten suspicion for acute glomerulonephritis. 4, 6

Essential Laboratory Evaluation

• Measure serum creatinine, BUN, and complete metabolic panel immediately to assess the severity of acute kidney injury and guide urgency of intervention. 4, 5, 6
• Obtain complement levels (C3, C4) to differentiate post-infectious glomerulonephritis (low C3) from lupus nephritis (low C3 and C4) from C3 glomerulopathy. 5, 2, 3
• Order antinuclear antibody (ANA), anti-double-stranded DNA (anti-dsDNA), and ANCA testing when vasculitis or lupus nephritis is suspected based on systemic symptoms. 1, 5, 2, 3
• Perform anti-glomerular basement membrane (anti-GBM) antibody testing if rapidly progressive glomerulonephritis is present, as anti-GBM disease requires urgent plasmapheresis. 2, 3

Kidney Biopsy: The Definitive Diagnostic Step

Proceed directly to kidney biopsy without delay when the combination of hematuria, proteinuria, and impaired renal function is present, as this triad indicates active glomerulonephritis requiring histologic diagnosis. 1, 2, 3

Indications for Urgent Biopsy

• Any reproducible proteinuria ≥0.5 g/24 hours with glomerular hematuria and/or cellular casts mandates renal biopsy, as clinical and serological tests cannot accurately predict biopsy findings. 1
• Rising serum creatinine or rapidly progressive glomerulonephritis (doubling of creatinine over 1–2 months) requires immediate biopsy to guide aggressive immunosuppression. 1, 3
• Systemic symptoms (fever, rash, arthralgia) accompanying nephritic syndrome suggest secondary glomerulonephritis (lupus, vasculitis) requiring specific immunosuppressive regimens. 1, 3

What the Biopsy Reveals

• Histopathology determines the etiology: immune complex-mediated GN (lupus, IgA nephropathy, post-infectious), ANCA-associated GN, anti-GBM GN, C3 glomerulopathy, or monoclonal immunoglobulin-mediated GN. 2, 3
• Pattern of injury (crescentic, necrotizing, diffuse proliferative, membranoproliferative) determines severity and guides intensity of immunosuppression. 2, 3
• Assessment of chronicity (glomerulosclerosis, tubular atrophy, interstitial fibrosis) predicts reversibility and long-term prognosis. 1, 2

Exclude Acute Interstitial Nephritis

Consider acute interstitial nephritis (AIN) in the differential diagnosis, particularly if the patient has recent medication exposure, as AIN can mimic glomerulonephritis but requires different management. 8, 9

Clinical Clues for AIN vs. Glomerulonephritis

• AIN typically presents with acute kidney injury, fever, eosinophilia, sterile pyuria, and only small-range proteinuria (<1 g/day), whereas glomerulonephritis presents with nephrotic-range proteinuria and dysmorphic RBCs. 8, 9
• Drug-induced AIN is the most common etiology; review all medications (NSAIDs, antibiotics, proton pump inhibitors) started within the past 1–3 months. 8, 9
• Kidney biopsy showing interstitial inflammation and edema without glomerular involvement confirms AIN, and treatment involves withdrawal of the offending agent ± glucocorticoids. 8, 9

Initial Imaging

• Obtain renal ultrasound to assess kidney size and echogenicity; enlarged echogenic kidneys suggest acute glomerulonephritis, while small echogenic kidneys indicate chronic disease with limited reversibility. 5
• Ultrasound is the preferred modality in children to evaluate anatomy before potential biopsy, but imaging does not replace histologic diagnosis in adults. 6

Immediate Management Pending Biopsy Results

Blood Pressure Control

• Target blood pressure <130/80 mm Hg in patients with proteinuria <1 g/day, and <125/75 mm Hg when proteinuria >1 g/day, using ACE inhibitors or ARBs as first-line agents. 1
• Hypertension accompanying hematuria and proteinuria is a hallmark of nephritic syndrome and requires aggressive management to prevent cardiovascular complications. 5, 7

Avoid Premature Immunosuppression

• Do not initiate immunosuppressive therapy before obtaining a kidney biopsy, as treatment differs substantially based on the specific diagnosis (e.g., cyclophosphamide for ANCA vasculitis vs. mycophenolate for lupus nephritis). 1, 3
• The exception is life-threatening rapidly progressive glomerulonephritis with pulmonary hemorrhage (Goodpasture syndrome), where empiric plasmapheresis and pulse methylprednisolone may be started before biopsy confirmation. 3

Specific Treatment Based on Biopsy Diagnosis

Lupus Nephritis (Class III/IV)

• Initiate mycophenolic acid (MMF target dose 3 g/day) or low-dose intravenous cyclophosphamide (total 3 g over 3 months) combined with glucocorticoids as first-line therapy for proliferative lupus nephritis. 1
• Combine with three consecutive pulses of intravenous methylprednisolone 500–750 mg, followed by oral prednisone 0.5 mg/kg/day for 4 weeks, tapering to ≤10 mg/day by 4–6 months to reduce cumulative steroid toxicity. 1
• Maintenance therapy with mycophenolate or azathioprine for at least 3 years is required to prevent relapse. 1

ANCA-Associated Vasculitis

• Use cyclophosphamide or rituximab combined with high-dose glucocorticoids for induction therapy in ANCA-associated glomerulonephritis. 1, 3
• Plasmapheresis should be added for severe disease with pulmonary hemorrhage or dialysis-dependent renal failure. 3

Post-Infectious Glomerulonephritis

• Supportive care with blood pressure control, diuretics for edema, and sodium restriction is the mainstay, as post-infectious GN is typically self-limited. 7, 3
• Low C3 levels support the diagnosis, and complement levels normalize within 6–8 weeks if the diagnosis is correct. 5, 3

IgA Nephropathy

• Long-term ACE inhibitor or ARB treatment is recommended when proteinuria >1 g/day, with uptitration to achieve proteinuria <1 g/day. 1
• Immunosuppression with corticosteroids is reserved for patients with persistent proteinuria >1 g/day despite maximal RAAS blockade and eGFR >50 mL/min. 1

Critical Pitfalls to Avoid

• Never attribute hematuria and proteinuria to anticoagulation or antiplatelet therapy without completing the full diagnostic work-up, as these medications may unmask underlying glomerular disease but do not cause it. 4, 5
• Do not delay biopsy while pursuing serologic testing; biopsy provides the definitive diagnosis and should be performed urgently when nephritic syndrome is present. 1, 2, 3
• Avoid treating presumed urinary tract infection with antibiotics when pyuria accompanies hematuria and proteinuria, as sterile pyuria is common in glomerulonephritis and AIN. 8, 9
• Do not assume normal blood pressure excludes glomerulonephritis; hypertension may develop later or be absent in some cases. 5
• Never ignore the combination of hematuria and proteinuria as benign; this strongly suggests underlying glomerular disease requiring nephrology evaluation. 5, 7