What is the estimated creatinine clearance (estimated glomerular filtration rate) for a 4‑year‑old child weighing 16.6 kg, height 106 cm, with a serum creatinine of 0.72 mg/dL?

Estimated Creatinine Clearance Calculation

For this 4-year-old child (weight 16.6 kg, height 106 cm, serum creatinine 0.72 mg/dL), the estimated GFR is approximately 61 mL/min/1.73 m² using the revised Bedside Schwartz equation.

Calculation Method

The revised Bedside Schwartz equation is the recommended formula for estimating GFR in children aged 1-16 years and should be used for this patient. 1

Formula Application

• For enzymatic creatinine assays (the current laboratory standard): GFR = 0.413 × [height (cm) / serum creatinine (mg/dL)] 1, 2, 3

  • Calculation: 0.413 × (106 cm / 0.72 mg/dL) = 60.8 mL/min/1.73 m²

• If your laboratory still uses the older Jaffe method: GFR = 0.55 × [height (cm) / serum creatinine (mg/dL)] 1, 2

  • Calculation: 0.55 × (106 cm / 0.72 mg/dL) = 81.0 mL/min/1.73 m²

Critical Implementation Steps

You must verify which creatinine assay your laboratory uses before applying the formula, as using the wrong constant leads to substantial errors. 2

• Enzymatic assays are strongly preferred for pediatric populations because Jaffe methods have significant interference from non-creatinine chromogens at the low creatinine concentrations typical in children 1, 2, 3
• The 0.413 constant is specifically calibrated for enzymatic methods and provides the most accurate results 2
• Never use the 0.55 Jaffe constant with enzymatic assays as this leads to GFR overestimation of approximately 33% 2

Clinical Interpretation

Normal Reference Range Context

• Normal GFR for children over 2 years of age is approximately 100-120 mL/min/1.73 m² when adjusted for body surface area 1
• This child's estimated GFR of ~61 mL/min/1.73 m² (using enzymatic method) suggests moderate renal impairment if confirmed 1

Important Caveats

Serum creatinine alone should never be used to assess renal function in children because it is affected by muscle mass, age, gender, and tubular secretion 1, 3

• Small changes in serum creatinine may represent relatively large changes in actual GFR in pediatric patients 4
• The Schwartz formula tends to overestimate GFR, particularly at lower GFR levels 3, 5
• Accurate height measurement is essential as the equation is height-dependent 2, 4

Alternative Assessment Methods

If this child has low muscle mass or the result seems inconsistent with clinical presentation, consider cystatin C-based GFR estimation as it is not affected by muscle mass, age, or gender 1, 2, 3

• Cystatin C levels of 1.06 mg/L predict GFR <80 mL/min/1.73 m² with 91% sensitivity and 81% specificity 1
• Combined creatinine and cystatin C equations provide superior accuracy 2
• Normal cystatin C values approach adult levels (0.51-0.98 mg/L) by 1 year of age 1

Clinical Action Algorithm

1. Confirm laboratory creatinine assay type (enzymatic vs. Jaffe) 2
2. Apply appropriate formula constant (0.413 for enzymatic, 0.55 for Jaffe) 1, 2
3. If GFR <90 mL/min/1.73 m²: Repeat measurement and consider cystatin C confirmation 1
4. If GFR <60 mL/min/1.73 m²: Evaluate for chronic kidney disease and assess for underlying causes 1
5. Monitor trends over time rather than relying on single measurements, especially in growing children 3, 4