Serial assessment of glomerular filtration rate in XXXX .

@entity1 @entity42317 @entity8 @entity8046 @entity10817 @entity1011
In @entity1 with @entity8 ( @entity8 ), previous studies have shown that @entity1011 clearance (CCr) overestimates true glomerular filtration rate as measured by inulin clearance ( @entity8046 ), and that among @entity1 the degree of overestimation is highly variable. We sought to determine whether the discrepancy between CCr and @entity8046 remains constant over time (months, years) in each individual @entity1 , and therefore whether serial measurements of CCr reliably reflect the direction and magnitude of change in @entity8046 . Twenty-five @entity1 with @entity8 underwent simultaneous determinations of CCr and @entity8046 performed two to four (mean 3.3) times over three years. In a given @entity1 , it was found that the ratio of CCr/ @entity8046 changed substantially over time (mean SD 0.16 with 95% confidence interval of 0.12 to 0.20). Thus, in about 32% of cases the ratio of CCr/ @entity8046 will vary more than +/- 16% from a previously measured value of CCr/ @entity8046 . @entity1 with both high and low values of @entity8046 showed similar variability in CCR/ @entity8046 over time. Variability in CCr/ @entity8046 was found regardless of whether @entity8046 was increasing, decreasing, or constant over time. In nearly one-half of all measurements of CCr, the corresponding change in @entity8046 was directionally discordant. @entity10817 and @entity42317 renal clearances correlated highly with @entity8046 (R2 = 0.99). We conclude that the discrepancy between CCr and @entity8046 can vary greatly over time in an individual @entity1 . Consequently, serial CCr does not accurately measure the direction or magnitude of change in glomerular filtration rate in @entity8 .
