Measured glomerular filtration rate (mGFR) is thought to be the best overall index of kidney function in children as well as adults, but it involves complex and time-consuming procedures, so it has limited use in routine clinical practice. As a result, estimated GFR (eGFR) is commonly used, explains Brenda Suh-Lailam, PhD, in the May issue of CLN. Suh-Lailam is the assistant director of clinical chemistry and mass spectrometry at Ann & Robert H. Lurie Children’s Hospital of Chicago and an assistant professor of pathology at Northwestern University Feinberg School of Medicine in Chicago.

Suh-Lailam cautions, however, that equations used to estimate GFR differ between adults and children. More than 10 equations currently exist for determining pediatric eGFR. Some are based on serum creatinine or cystatin C individually, and others include a combination of biomarkers. Pediatric eGFR equations commonly account for other variables, such as age, sex, and height or weight. Estimating equations that include a combination of biomarkers correlate better with mGFR, when compared to eGFR equations that employ only creatinine or cystatin C.

The best equations for eGFR in children are those developed and validated within the CKiD (Chronic Kidney Disease in Children) study cohorts, which were published in 2009 and 2012. Commonly referred to as the CKiD Schwartz equations, these incorporate serum creatinine (Scr), cystatin C (Scys) and blood urea nitrogen (BUN) with variables for height and sex.

When using eGFR equations, it is imperative to remember that an equation performs best when applied to a similar patient population and using measurement methods that are equivalent to those used in the equation’s development. The CKiD Schwartz equations were developed using data from children with chronic kidney disease and an isotope dilution mass spectrometry-traceable enzymatic creatinine method. They have been optimized for the type of cystatin C assay used (e.g. 2009 CKiD Schwartz for turbidimetric cystatin C and 2012 CKiD Schwartz for nephelometric cystatin C).

Pick up the May issue of CLN to read more about assessing kidney function in children, including what to do if measurement of cystatin C is not readily available.