GFR = k × Height/Serum creatinine

Height represents the body height measured in centimeters, and serum creatinine is measured in mg/dL. The constant k is directly proportional to the muscle component of the body and varies with age based on the laboratory assay used to measure serum creatinine .

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Enzymatic methodology using isotope dilution mass spectrometry – When the serum creatinine is determined using enzymatic methodology, the value for k is 0.413 mg/dL (36.5 micromol/L) for all children with chronic kidney disease between ages 1 and 16 years. This is what called Bedside Schwartz method.

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Jaffe method – When serum creatinine is measured by the Jaffe method, the values for k are:

• Premature infants: through the first year of life: 0.33 mg/dL (29.2 micromol/L)
• Term infants: through the first year of life: 0.45 mg/dL (39.8 micromol/L)
• Children and adolescent girls: 0.55 mg/dL (48.6 micromol/L)
• Adolescent boys: 0.7 mg/dL (61.9 micromol/L)

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Ref:

• Srivastava T, Alon US, Althahabi R, Garg U. Impact of standardization of creatinine methodology on the assessment of glomerular filtration rate in children. Pediatr Res. 2009 Jan;65(1):113-6. doi: 10.1203/PDR.0b013e318189a6e8. PMID: 18703997.
• Schwartz GJ, Muñoz A, Schneider MF, Mak RH, Kaskel F, Warady BA, Furth SL. New equations to estimate GFR in children with CKD. J Am Soc Nephrol. 2009 Mar;20(3):629-37. doi: 10.1681/ASN.2008030287. Epub 2009 Jan 21. PMID: 19158356; PMCID: PMC2653687.