The clinical utility of serum creatinine measurement vs calculated glomerular filtration rate in the assessment of renal function in the premature infant.

The ability to assess the glomerular filtration rate (GFR) without the necessity of collecting urine in premature infants would be of significant clinical benefit. In 1986, the modified Schwartz formula (MSF = 0.33 x length (cm)/plasma creatinine (mg/dL)) was developed. In the MSF, GFR was estimated in premature infants during the first post-natal year. The goal of the present study was to test the applicability of the MSF in premature infants during the neonatal period and to evaluate the clinical use of serum creatinine (Cr) as a predictor of GFR. In 42 premature infants of mean (+/-SD) birthweight 1506.6 (+/-388.8) g, gestational age 31.3 (+/-1.7) wks and post-natal age 14.7 (+/-8.3) d, the correlation between GFR, estimated by endogenous creatinine clearance (ECrC), was compared with the serum Cr and with GFR estimated by the MSF. The correlation coefficient between ECrC and serum Cr was 0.6789 and between estimated GFR derived from ECrC and MSF, 0.4657. In premature infants during the neonatal period, serum Cr has a better correlation with GFR than with MSF. When serum Cr is less than 0.9 mg/dL, the 95% confidence interval suggests that at least 89% of the infants can be expected to have an ECrC within the normal range.