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What is the Schwartz formula and when is it used?
The bedside Schwartz formula (2009) estimates the glomerular filtration rate in children and adolescents between 1 and 18 years of age, using 0.413 multiplied by height in centimetres, divided by serum creatinine in mg/dL. It uses height instead of age and sex because, in children, muscle mass (the source of creatinine) grows along with height.
Why is the adult formula not used in children?
Adult formulas such as CKD-EPI were developed and validated in people over 18 years of age. Children have a much smaller and constantly changing muscle mass, so the same creatinine value means something completely different in a 6-year-old than in an adult. Applying an adult formula to a child would give systematically wrong results.
How is the result interpreted in children?
As a reference, after the age of 2 a value of about 90 or more is considered normal, while persistently lower values may point to reduced kidney function. In children under 2, normal values are naturally lower because the kidney is still maturing. Interpretation rests with the paediatrician or paediatric nephrologist, in the context of the whole assessment.
What are the limitations of the estimate in children?
The result depends on the laboratory method used for creatinine (the formula assumes a standardised IDMS method, used by most modern laboratories), and in children with unusual muscle mass (for example neuromuscular disease or malnutrition) the estimate may be inaccurate. The formula does not apply to infants under 1 year of age. An abnormal value is always confirmed by repeat testing and medical assessment.