PLASMA CREATININE LEVEL AND CREATININE CLEARANCE AS TESTS OF RENAL FUNCTION

In hospital patients with no evidence of renal disease, the mean value (and standard deviation) for plasma creatinine concentration was 0.93±0.14 milligramme per 100 millilitres in 14 males, and 0.73±0.14 milligramme per roo millilitres in 18 females. The corresponding endogenous creatinine clearances were 108±16 and 104±14 millilitres per minute respectively. Reasons are advanced for considering this clearance to be equivalent to the glomerular filtration rate (G.F.R.). Blood urea nitrogen content, urea clearance and plasma creatinine content were compared as measures of the G.F.R. in 50 hospital patients referred for investigation of renal function. There was a highly significant correlation between urea clearance and G.F.R., and the latter could be predicted from urea clearance with some precision (standard deviation of estimate, 18.7 millilitres per minute). With the blood urea nitrogen content alone a less significant correlation was obtained, and the G.F.R. could be predicted less precisely (standard deviation of estimate, 24.7 millilitres per minute). The plasma creatinine content showed a highly significant correlation with the G.F.R., and was at least as good as urea clearance for estimating the G.F.R., particularly if males and females were separated. Comparison of the plasma creatinine content with the G.F.R. in a larger group on 136 occasions showed a highly significant correlation, and the G.F.R. could be estimated from the plasma creatinine content with a standard deviation of 13.6 millilitres per minute. The G.F.R. for males was best expressed by and for females by It was concluded that the measurement of true plasma creatinine content provides a better indication of renal function than tests in common use based on measurements of urea.