VARIABILITY IN THE URINARY EXCRETION OF GROWTH HORMONE (GH) AND CREATININE IN CHILDHOOD

Abstract

As a basis for assessment of the clinical validity of urinary GH measurements in children, the variability in renal handling of GH was compared to that of creatinine in 93 healthy children (aged 4-16 years), 20 of normal stature and 73 with growth disorders. 10 were classified as GH deficient (GHD), 48 as short normal (SN) and 15 had Turner syndrome (TS). 5 overnight urine samples were collected over 2 weeks, and the variability of excretion expressed as a coefficient of variation (CV) of the total overnight amount of GH or creatinine. There was considerable night to night variability in the excretion of both substances:* p<0.05 compared to Normal + SN, #p<0.05 compared to Normal.Assay variation rather than a change in renal protein handling accounted for the large variation in low uGH concentrations, thus contributing to the high uGH CV of the GHD group. Increasing the number of samples collected (upto 5) decreased the expected sample variation (error) for uGH but not significantly in all groups, and reduced the convenience and practicality of the test. These results indicate that variation in GH and creatinine excretion is considerable in both normal children and those with growth disorders. The use of multiple samples (upto 5) does not significantly reduce the variability inherent in uGH measurement.