Re-evaluation of plasma creatinine concentration in normal pregnancy.

Renal function improves during pregnancy, a well-known clinical manifestation of this being a fall in plasma creatinine concentration. However, there are no secure data upon which to determine the extent to which creatinine concentration changes during pregnancy. A well-defined reference range is important for the correct interpretation of results, but to date one has not been published. This study uses a large cohort of women experiencing normal pregnancy, modern laboratory technique and robust statistical analysis to construct a cross-sectional reference interval. This study shows that the upper limit of normal for creatinine in pregnancy is higher than previously suggested, although still much lower than outside pregnancy. Values for the upper limit of normal can be taken as 85 micromol/l, 80 micromol/l and 90 micromol/l in the first, second and third trimesters of pregnancy respectively. This information is important for the clinical assessment of a result from a pregnant woman, particularly in conditions such as pre-eclampsia where abnormalities of renal function may occur.