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$$\text{GFR (mL/min/1.73m}^2\text{)} = k \times \frac{\text{Height (cm)}}{\text{Serum creatinine (mg/dL)}}$$
Once glomerular disease is identified, the assessment of kidney function involves determining the presence and extent of impairment through an estimation of the glomerular filtration rate (GFR). A decrease in GFR indicates potential progression of the underlying condition or the emergence of an additional and often reversible issue, such as reduced renal blood flow due to dehydration.
The most commonly employed method for estimating GFR involves measuring the level of serum creatinine and calculating creatinine clearance based on this measurement.
GFR estimation can be accomplished using the Schwartz formula, which factors in serum creatinine levels along with age, height, and sex (in adolescents).
The constant k is directly proportional to the muscle component of body and varies with age. The estimated GFR also depends on the laboratory assay used to measure serum creatinine.
Jaffe method
When serum creatinine is measured by Jaffe method and the measurement is expressed as mg/dL, the value for k is
0.33 in premature infants through the first year of life,
0.45 for term infants through the first year of life,
0.55 in children and adolescent girls, and
0.7 in adolescent boys.
When the measurement is expressed as mcmol/L, the value for k is
29.2 in premature infants through the first year of life,
39.8 for term infants through the first year of life,
48.6 in children and adolescent girls, and
61.9 in adolescent boys.
Enzymatic method
When serum creatinine is determined using enzymatic method for all children with CKD between ages 1 and 16 years, the value for k is:
0.413 when the measurement is expressed as mg/dL.
36.5 when the measurement is expressed as mcmol/L.
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; 65:113.
Schwartz GJ, Munoz A, Schneider MF, et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol 2009; 20:629.
