Aim: The purpose of this study was to determine the repeatability and validity of 2 x 2 hour creatinine clearance, and the validity of creatinine clearances estimated by equations.
Patients and methods: In 30 patients two 2 x 2 h and two 24-h creatinine clearances were performed on consecutive days. In addition, creatinine clearances estimated by 4 different equations were calculated. Two by two hour creatinine clearance provided a measurement of GFR as valid as 24-h creatinine clearance.
Results: We found, that 2 x 2 h creatinine clearance was well repeatable with a mean difference between 2 repeated measurements of 0.8 ml/min and low coefficients of repeatability of 14.5 ml/min. The validity of 2 x 2 h creatinine clearance, assessed by the mean difference between 2 x 2 and 24-h creatinine clearances, was 1.2 ml/min with tight 95% limits of agreement with a range from -8.1 to 10.5 ml/min. This high degree of repeatability and validity was present over the entire range of renal function (6-141 ml/min). As 2 x 2 h creatinine clearance is more simple and rapid than 24-h creatinine clearance, results are obtained on the same day and easy, but repeatable and valid day-to-day monitoring of renal function is possible. In addition, the two times two hour clearances allow for quality control. In contrast, estimated creatinine clearances show only poor validity.
Conclusion: Because of the high degree of repeatability and validity, 2 x 2 h creatinine clearance may replace 24-h creatinine clearance as the standard method to determine renal function in clinical practice.