In a 15‑year‑old adolescent boy presenting with one‑week facial puffiness and pedal edema, proteinuria (urine albumin ++), pyuria (30‑35 pus cells), microscopic hematuria (4‑5 red blood cells), impaired renal function (serum creatinine 1.6 mg/dL), normal complement C3 and C4, normal anti‑streptolysin O titre, urine protein‑creatinine ratio ≈2 g/g, and a recent skin infection one month ago, what further work‑up and management steps are indicated?

Workup and Management of Nephritic Syndrome with Pyuria in an Adolescent

This 15-year-old requires urgent renal biopsy after initial workup, as the combination of significant proteinuria (PCR 2 g/g), hematuria, pyuria, elevated creatinine, and normal complements with recent skin infection most likely represents post-infectious glomerulonephritis (PIGN) or IgA nephropathy—both requiring histologic confirmation to guide immunosuppressive therapy and predict prognosis. 1

Immediate Diagnostic Workup

Laboratory Investigations

• Complete metabolic panel to assess albumin (likely low given edema), total protein, electrolytes, and confirm renal dysfunction 1
• Urinalysis with microscopy to identify dysmorphic RBCs (>80% indicates glomerular disease) and red cell casts (pathognomonic for glomerulonephritis) 1, 2
• Repeat ASO titer with anti-DNase B since ASO can normalize by 3-4 weeks post-streptococcal infection; anti-DNase B remains elevated longer and is more sensitive for skin infections 3
• Hepatitis B and C serology, HIV testing to exclude secondary causes of glomerulonephritis 4
• ANA, anti-dsDNA, and repeat C3/C4 to definitively exclude lupus nephritis despite initial normal complements 1
• Serum albumin to confirm nephrotic-range proteinuria syndrome (albumin <2.5 g/dL with PCR >2 g/g defines nephrotic syndrome) 4

Imaging

• Renal ultrasound immediately to assess kidney size, echogenicity (increased in acute glomerulonephritis), rule out structural abnormalities, and evaluate safety for biopsy 5, 6, 1
• Enlarged, echogenic kidneys support acute glomerulonephritis 5

Critical Clinical Reasoning

Why Normal Complements Don't Exclude PIGN

While classic PIGN shows low C3, complement levels normalize 6-8 weeks after infection onset—this patient's skin infection occurred 1 month ago, placing him in the window where C3 may have already recovered 3. The 7-14 day latency between skin infection and symptom onset is classic for PIGN 3.

The Pyuria Dilemma

The significant pyuria (30-35 WBCs) is unusual but does not exclude glomerulonephritis—sterile pyuria occurs in proliferative glomerular diseases. However, rule out concurrent UTI with urine culture before proceeding to biopsy 5.

Why Biopsy Is Essential Here

The combination of hematuria, proteinuria (PCR >0.2 g/g on multiple specimens), and elevated creatinine mandates nephrology referral and likely biopsy 1. Unlike isolated microscopic hematuria without proteinuria (where imaging is often unnecessary 5), this patient has:

• Nephrotic-range proteinuria (PCR 2 g/g) requiring urgent evaluation 4, 1
• Acute kidney injury (creatinine 1.6 mg/dL in a 15-year-old) suggesting active glomerular inflammation
• Combined hematuria and proteinuria, which strongly indicates glomerular disease requiring histologic diagnosis 4, 1

The differential includes:

• PIGN (most likely given skin infection history and age) 3
• IgA nephropathy (most common glomerulonephritis in adolescents, can present identically) 1
• Rapidly progressive glomerulonephritis (less likely with normal complements but cannot exclude)

Management Algorithm

Immediate Supportive Care (Start Today)

1. Strict fluid restriction (maintenance fluids only) and sodium restriction (<2 g/day) to manage edema 3
2. Loop diuretic (furosemide 1-2 mg/kg/dose) for symptomatic edema relief 3
3. Antihypertensive therapy if BP elevated (target <95th percentile for age/height)—use ACE inhibitor or ARB for dual benefit of BP control and proteinuria reduction 4
4. Monitor daily weights, strict intake/output, and watch for complications (hypertensive encephalopathy, heart failure, pulmonary edema) 3

Nephrology Referral (Urgent, Within 24-48 Hours)

Immediate pediatric nephrology consultation is mandatory given combined hematuria-proteinuria, elevated creatinine, and nephrotic-range proteinuria 1. This is non-negotiable.

Renal Biopsy Timing

• Perform biopsy after ultrasound confirms safe anatomy and coagulation studies are normal 5
• Do not delay biopsy waiting for "spontaneous improvement" in this scenario—the elevated creatinine and nephrotic-range proteinuria indicate active disease requiring diagnosis 4
• If biopsy confirms PIGN, most cases resolve spontaneously with supportive care alone (98.3% complete recovery) 3
• If biopsy shows IgA nephropathy, crescentic GN, or other proliferative disease, immunosuppression may be required and cannot be initiated without histologic confirmation

Post-Biopsy Management Depends on Histology

For PIGN (if confirmed):

• Continue supportive care only
• Monitor for resolution over 6-12 weeks
• Excellent prognosis (98% complete recovery) 3

For IgA nephropathy or other proliferative GN:

• Initiate ACE inhibitor/ARB therapy targeting proteinuria <0.5-1 g/day 4
• Consider corticosteroids or other immunosuppression based on biopsy severity (crescents, interstitial fibrosis)
• Long-term monitoring for chronic kidney disease progression

Common Pitfalls to Avoid

• Do not assume normal ASO excludes post-streptococcal disease—check anti-DNase B, especially after skin infections 3
• Do not assume normal complements exclude PIGN—they normalize after 6-8 weeks 3
• Do not treat pyuria as UTI without culture confirmation—sterile pyuria is common in glomerulonephritis 5
• Do not delay nephrology referral for combined hematuria-proteinuria with renal dysfunction—this is a medical emergency requiring specialist evaluation 1
• Do not start empiric immunosuppression without biopsy—PIGN requires only supportive care, while other diagnoses need specific therapy 3