Estimating and Managing Glomerular Filtration Rate in Children
For children over 2 years of age, GFR should be estimated using validated pediatric-specific equations, with the revised Bedside Schwartz equation being the preferred method for routine clinical use. 1, 2
Recommended GFR Estimation Methods for Children
- The revised Bedside Schwartz equation is the primary recommended formula for estimating GFR in children: eGFR (ml/min per 1.73 m²) = 0.413 × (height in cm) ÷ (serum creatinine in mg/dl) 1, 2
- For children with low muscle mass (e.g., those with severe neurological involvement), cystatin C-based GFR measurements are preferred as creatinine-based equations may overestimate kidney function 3
- Combined creatinine and cystatin C-based equations (such as the CKiD2 equation) provide superior accuracy, especially in children with solitary functioning kidneys 4, 3
- When height measurements are unavailable, height-independent equations can be used: eGFR = 107.3/(Scr/Q), where Q is the median serum creatinine for healthy children of that age 5
Laboratory Considerations for Pediatric GFR Assessment
- Enzymatic creatinine assays should be used in children rather than Jaffe assays due to the higher relative contribution of non-creatinine chromogens in pediatric samples 3
- Laboratories measuring creatinine in infants or small children must ensure their quality control process includes the lowest end of the expected range of values 3
- In neonates, special consideration is needed due to high prevalence of icteric and hemolyzed samples 3
- An eGFRcr level <90 ml/min per 1.73 m² should be flagged as "low" in children and adolescents over 2 years of age 3
Monitoring and Management of GFR in Children
- The trend of GFR assessments over time is more relevant than a single measurement, especially in growing children 3
- GFR should be assessed periodically and correlated with somatic growth goals to evaluate progression and need for renal replacement therapy 3
- For children with chronic kidney disease, monitoring should include assessment of albuminuria alongside GFR measurements 3
- In children with tuberous sclerosis complex or other conditions affecting muscle mass, cystatin C-based eGFR measurements are recommended 3
Special Considerations in Pediatric GFR Assessment
- Small changes in serum creatinine may represent relatively large changes in actual GFR in pediatric patients 2
- For children with rapid progression (sustained decline in eGFR >5 ml/min/1.73 m²/year), more frequent monitoring and specialist referral are recommended 3
- When no prior creatinine is available within the previous 3 months, baseline kidney function can be imputed by assuming a normal GFR of 100 ml/min/1.73 m² and using the patient's height 2
- For children with polycystic kidney disease or other genetic kidney disorders, regular monitoring of GFR is essential for early intervention 3
Pitfalls and Caveats in Pediatric GFR Assessment
- Standard eGFR formulae may overestimate GFR in children with low muscle mass 3, 6
- Accurate height measurement is necessary for calculating eGFR using the Schwartz formula, which can be challenging in sick or ventilated patients 2
- Misclassification of CKD stage can occur with all estimation equations, ranging from 22-44% depending on the equation used 4
- Gold standard GFR measurements (inulin clearance) are rarely used in clinical practice due to practical difficulties but remain the reference standard for research 6
By following these guidelines for estimating and monitoring GFR in children, clinicians can better identify kidney dysfunction early, implement appropriate interventions, and potentially slow progression of kidney disease in the pediatric population.