Can two-, four- or eight-hour urine collections after voluntary voiding be used instead of twenty-four-hour collections for the estimation of creatinine clearance in healthy subjects?

Abstract

The accuracy of creatinine clearance estimations obtained from 4-hour (16:00-20:00, 20:00-24:00, 08:00-12:00, 12:00-16:00) and 8-hour (16:00-24:00, 24:00-08:00 and 08:00-16:00) urine collections and the Cockcroft Gault formula compared with the standard 24-hour collection, as well as the cyclical variation in creatinine excretion were studied in a group of 22 healthy subjects (Serum creatinine < 1.5 mg/dl, Blood Urea Nitrogen < 50 mg/dl) after voluntary voiding. The mean 4-hour and 8-hour creatinine clearances were not significantly different from the 24-hour values. Clearance values from 8-hour collections between 24:00-08:00 and 16:00-24:00 were found to be the most accurate and gave the best correlations. Furthermore only the mean absolute percentage deviations of the 8-hour from the 24-hour clearance values were significantly less than 20%. Significant cyclical variations in creatinine clearance over 24 hours were not observed. Time intervals between 23:00-07:00 and 07:00-09:00 were chosen for the comparisons between 8-hour, 2-hour, Cockcroft Gault creatinine clearance estimations and the 24-hour values in 21 healthy subjects. The mean 2-hour and 8-hour creatinine clearances were not significantly different from the 24-hour values. However, once again only the 8-hour clearance values differed by less than 20% from the 24-hour values and they were more accurate and better correlated than the 2-hour values. As expected, in both groups of subjects, the percentage of clearance values that deviated by more than 20% from the 24-hour values decreased as the length of the collection times increased. The Cockcroft Gault formula in both groups of volunteers gave less accurate clearance estimations, smaller correlation coefficients (not statistically significant in Group I subjects) and percentage deviations from the 24-hour values greater than 20%. Undetected early stage renal insufficiency in three volunteers and the use of actual instead of normalized Scr values may have been the cause of these poor clearance estimations. In healthy subjects (Scr < 1.5 mg/dl) 24-hour creatinine clearance may be estimated from an 8-hour urine collection with voluntary voiding if a 20% deviation from the 24-hour value is considered clinically acceptable.