Establishing age/sex related serum creatinine reference intervals from hospital laboratory data based on different statistical methods.

This is a retrospective study on a large hospital database to establish age- and sex-related mean values and reference ranges for serum creatinine (Scr), obtained with an IDMS-traceable, enzymatic method, in a Caucasian population. The database was filtered for unique entries to reduce the presence of correlated and pathological data. Three different statistical methods, a non-parametric method, the Bhattacharya procedure and a non-linear fit of the cumulative Gaussian distribution were used to estimate the serum creatinine-age dependency for men and women, from birth till 100 years of age. Scr increases with age, equal for boys and girls, up to 14 years and with a much steeper slope for boys than for girls between 14 and 20 years. We show that the Scr-age pattern is constant between 20 and 70 years with a mean of 0.90 mg/dL [0.63-1.16 mg/dL] for men and 0.70 mg/dL [0.48-0.93 mg/dL] for women. Above 70, Scr starts to slowly increase again. Indirect methods confirm the available reference intervals from healthy-volunteer studies and add information on age-periods not covered by these studies. As such, indirect methods can be used complementary to healthy-volunteer studies.