Alejandro Quiroga, MD, Pediatric Nephrologist
Spectrum Health Medical Group
Helen DeVos Children’s Hospital

I’m sure that few primary care physicians have the time or inclination to read the Clinical Journal of the American Society of Nephrology, but there was a very interesting editorial in the most recent issue about glomerular filtration rate (GFR) in children. We see quite a few patients referred to us for abnormal GFRs when, in fact, their GFR is normal. The challenge comes with the fact that figuring the estimated GFR (eGFR) in a child requires a calculation that isn’t required in normal adults (you can estimate the GFR in adults using the MDRD formula). Thus, the values you receive back from the lab may show the result as high or low because the lab does not perform that calculation and busy pediatricians may also forget to do it.

In addition, as the editorial by Fadrowski and Furth noted, today there are two commonly used estimating equations for children. There is the Schwartz equation, on which most of us trained, and the newer CKiD equation developed the ongoing National Institutes of Health-sponsored Chronic Kidney Disease in Children (CKiD) Study. (Full disclosure: Helen DeVos Children’s Hospital participates in the CKiD study).

I still recommend the Schwartz formula, since it is what most of us are familiar with. In addition, there is some suggestion that the CKiD misclassifies or underestimates median GFR (mGFR) in children with normal or mildly decreased kidney function^1-3

As you may recall, with the Schwartz formula you multiply the height of the child against a constant that depends on the age (infant 0.45, child 0.55) then divide the result by the serum creatine mg/dL (you can always train your staff to use an online calculator http://www-users.med.cornell.edu/~spon/picu/calc/crclschw.htm).  A result of ³90 ml/min per 1.73 m² is generally considered “normal” kidney function. The “normal” kidney function using the CKiD equation requires further validation, noted the authors of the aforementioned editorial.

Confused? Don’t be. When in doubt—and before sending a child to the emergency department—check with a pediatric nephrologist. We’re happy to help.

Alejandro Quiroga, MD, is a pediatric nephrologist at Helen DeVos Children’s Hospital, Grand Rapids, Michigan

References

1. Staples A, LeBlond R, Watkins S, Wong C, Brandt J: Validation of the revised Schwartz estimating equation in a predominantly non-CKD population. Pediatr Nephrol 25: 2321–2326, 2010
2. Pottel H, Mottaghy FM, Zaman Z, Martens F: On the relationship between glomerular filtration rate and serum creatinine in children. Pediatr Nephrol 25: 927–934, 2010
3. Qayed M, Thompson A, Applegate K, Haight A, Rogatko A, Chiang KY, Horan J: Is the updated Schwartz formula appropriate for assessing renal function prior to hematopoietic stem cell transplantation? Pediatr Blood Cancer 55: 199–201, 2010