What laboratory and imaging studies are recommended to evaluate a patient with suspected acute glomerulonephritis?

Laboratory and Imaging Evaluation for Acute Glomerulonephritis

For suspected acute glomerulonephritis, obtain urinalysis with microscopy, urine culture, serum creatinine, complement levels (C3, C4), anti-streptolysin O (ASO) or anti-DNase B titers, and antinuclear antibodies (ANA); imaging is generally not required unless complications are suspected. 1, 2, 3

Essential Laboratory Tests

Initial Urinary Studies

• Urinalysis with microscopy is the cornerstone diagnostic test, showing hematuria (often with red blood cell casts), proteinuria, and pyuria in acute glomerulonephritis 1, 3
• Microscopic examination demonstrating >5 WBC/μL has 90-96% sensitivity for detecting renal inflammation 4
• Urine culture should be obtained before initiating any antibiotics to identify potential infectious triggers 4
• Red blood cell casts are pathognomonic for glomerular inflammation and help distinguish glomerulonephritis from other causes of hematuria 1

Serologic Testing

• Serum complement levels (C3, C4) are critical: depressed C3 with normal C4 suggests post-infectious glomerulonephritis or C3 glomerulopathy, while low C3 and C4 suggest lupus nephritis or cryoglobulinemia 1, 5
• Anti-streptolysin O (ASO) or anti-DNase B titers should be obtained when post-streptococcal glomerulonephritis is suspected, as these provide serologic evidence of recent streptococcal infection 6, 5
• Antinuclear antibodies (ANA) and anti-double stranded DNA (anti-dsDNA) are essential to evaluate for lupus nephritis 1, 2
• ANCA (antineutrophil cytoplasmic antibody) testing identifies ANCA-associated glomerulonephritis 2, 3
• Anti-GBM (anti-glomerular basement membrane) antibodies should be checked when rapidly progressive glomerulonephritis is suspected 2, 3

Renal Function Assessment

• Serum creatinine and blood urea nitrogen (BUN) assess the degree of renal impairment 1, 3
• Electrolytes should be monitored as sodium and water retention commonly occur 1

Imaging Studies

When Imaging Is NOT Indicated

• Routine imaging is not required for uncomplicated acute glomerulonephritis where the diagnosis is established by clinical presentation and laboratory findings 7, 4
• The diagnosis of glomerulonephritis is primarily clinical and serologic, not radiographic 1, 2

When Imaging IS Indicated

• Renal ultrasound should be obtained if urinary tract obstruction is suspected, particularly in patients with a history of urolithiasis or anatomic abnormalities 7, 4
• Ultrasound is preferred in pregnant patients to avoid radiation exposure 7, 4
• Contrast-enhanced CT may be warranted if complications such as renal or perinephric abscess are suspected, though this is uncommon in primary glomerulonephritis 7, 4

Definitive Diagnosis

Renal Biopsy Indications

• Renal biopsy is the gold standard for definitive diagnosis when the etiology of glomerulonephritis is uncertain, when treatment decisions require histologic confirmation, or when the clinical course is atypical 2, 3
• Biopsy determines the specific type of glomerulonephritis (immune complex-mediated, ANCA-associated, anti-GBM, monoclonal immunoglobulin-mediated, or C3 glomerulopathy), the pattern of injury (crescentic, necrotizing, proliferative), and the degree of chronicity 2
• Ancillary studies including immunofluorescence and electron microscopy are essential components of the biopsy evaluation 2

Clinical Pitfalls to Avoid

• Do not delay urine culture until after antibiotic initiation, as this compromises the ability to identify infectious triggers 4
• Do not rely solely on imaging to diagnose glomerulonephritis, as parenchymal changes may be subtle or absent on ultrasound and CT 7, 4
• Do not assume all hematuria is glomerular without microscopy; the presence of red blood cell casts is essential to confirm glomerular origin 1
• Do not overlook complement levels, as the pattern of complement consumption significantly narrows the differential diagnosis 1, 5
• In post-streptococcal glomerulonephritis specifically, the classic triad of hematuria, edema, and hypertension combined with depressed C3 and elevated ASO titers usually establishes the diagnosis without need for biopsy 6, 5