How this calculator works
The bedside equation uses height and serum creatinine. The full 2009 CKiD equation adds cystatin C, BUN and a sex coefficient. Both report GFR indexed to 1.73 m², not absolute kidney clearance. The original study involved children aged 1 to 16 years with chronic kidney disease and measured GFR mainly in the 15 to 75 mL/min/1.73 m² range. Its cystatin C assay was turbidimetric; later assay-standardised equations are different. These historical equations are not neonatal equations and should not be substituted for an age- and assay-appropriate current clinical method. The result is an estimate for information only and is not medical advice.
Formula
Bedside eGFR = 0.413 × height(cm)/creatinine(mg/dL). Full 2009 CKiD eGFR = 39.1 × (height(m)/creatinine)^0.516 × (1.8/cystatin C)^0.294 × (30/BUN)^0.169 × 1.099 if male × (height(m)/1.4)^0.188.
Worked example
At 140 cm and creatinine 1 mg/dL, bedside eGFR is 57.82 mL/min/1.73 m². At 100 cm and 0.5 mg/dL it is 82.6 mL/min/1.73 m²; accuracy outside the original CKD range is less certain.
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Frequently asked questions
Is BUN the same number as urea?
No. The full equation specifically requires BUN in mg/dL. Do not enter serum urea in mmol/L into that field.
Why name the cystatin C assay?
The 2009 equation was fitted to a particular turbidimetric assay. Standardisation and later equations changed the calibration, so the formula cannot be freely interchanged.
Does this return absolute clearance?
No. The result is indexed to 1.73 m² of body surface area. It is not a stand-alone dosing recommendation.