eGFR Schwartz Result of 172.1 in an 11-Year-Old with SLE
An eGFR of 172.1 mL/min/1.73 m² by the Schwartz equation in an 11-year-old with SLE indicates hyperfiltration and excellent kidney function, but requires careful monitoring because the Schwartz equation systematically overestimates GFR at higher values and this patient remains at risk for future lupus nephritis. 1, 2, 3
Understanding the Result
The Schwartz equation overestimates true GFR, particularly at values above 60 mL/min/1.73 m², with studies showing the equation can overestimate by 19-26% in children with normal or elevated kidney function 4, 3. This means the true GFR is likely lower than 172.1 mL/min/1.73 m², probably in the range of 120-140 mL/min/1.73 m² 3.
- Normal pediatric GFR after age 2 years is approximately 100 mL/min/1.73 m² when adjusted for body surface area, similar to adults 1
- Hyperfiltration (GFR >135 mL/min/1.73 m²) can occur in early kidney disease and may paradoxically indicate glomerular stress rather than optimal function 3
Clinical Implications for SLE Management
This normal-to-elevated eGFR does NOT exclude lupus nephritis, as kidney biopsy findings can be significant even with preserved GFR 1.
Monitoring Requirements
- Check for proteinuria using first morning urine protein-to-creatinine ratio (UPCR) - any reproducible proteinuria ≥0.5 g/24h (or UPCR ≥0.5 g/g) warrants consideration of kidney biopsy 1
- Examine urine sediment for glomerular hematuria (dysmorphic red blood cells) and cellular casts, which indicate active glomerular disease even with normal GFR 1
- Monitor serologic markers including anti-dsDNA antibodies and complement levels (C3, C4) to assess for lupus activity 1
- Repeat eGFR measurements every 3-6 months to detect trends, as declining GFR is more clinically significant than a single value 2
Biopsy Considerations
Kidney biopsy should be performed if any of the following develop 1:
- Proteinuria ≥0.5 g/24h (or UPCR ≥0.5 g/g), especially with glomerular hematuria
- Cellular casts in urine sediment
- Unexplained decline in GFR of ≥25% from baseline
- Persistent isolated glomerular hematuria after excluding other causes
Do not delay biopsy based on preserved GFR alone - the threshold for biopsy should be low in SLE because clinical and laboratory tests cannot accurately predict histological findings 1.
Technical Considerations
The revised Bedside Schwartz equation requires enzymatic creatinine assays (isotope dilution mass spectrometry-traceable) rather than Jaffe methods, as non-creatinine chromogens disproportionately affect the low creatinine values in children 1, 2.
- Accurate height measurement is essential for the Schwartz calculation: eGFR = 0.413 × [height (cm) / creatinine (mg/dL)] 1, 2
- If muscle mass is reduced (which can occur with chronic illness or corticosteroid use), consider cystatin C-based GFR estimation as creatinine-based equations may overestimate function 1, 2
Common Pitfalls to Avoid
- Do not assume normal kidney function based solely on elevated eGFR - lupus nephritis can be present with preserved or even elevated GFR 1, 5
- Do not ignore low-grade proteinuria (<0.5 g/24h) if accompanied by active urinary sediment or declining GFR trends 1
- Do not use serum creatinine alone to assess kidney function in children, as it is heavily influenced by muscle mass, age, and gender 1
- Do not delay immunosuppressive treatment if biopsy shows active lupus nephritis, even with preserved GFR 1, 6
Long-Term Prognosis
Podocyte injury can occur in lupus nephritis even with preserved GFR and is associated with poor long-term kidney outcomes 5. Regular monitoring is essential because:
- Children with SLE have more severe lupus nephritis at presentation compared to adults, with increased damage accrual 1
- Early detection and treatment of lupus nephritis significantly improves long-term outcomes, including prevention of progression to end-stage kidney disease 1, 6
- Transition to adult nephrology care requires coordinated planning to ensure treatment adherence and optimize outcomes 1