Reproducibility of the measurements of creatinine clearance in patients with a stable renal function.

In everyday practice the measurement of creatinine clearance (CCr) is used for the evaluation of the renal function. Since large body of evidence points to the inaccuracy of this test, we decided to check whether a repeated measurement of CCr might improve the assessment of the glomerular filtration rate. The study comprised 233 subjects, 105 females and 128 males, aged 22-80 years (mean age: 50.8 +/- 12.8 years) with the history of renal stones and a stable renal function, e.g. without changes in plasma creatinine. In every patient CCr was measured twice. Thereafter, all studied subjects were sorted by the increasing absolute values of the difference between two measurements of CCr e.g. as the difference between two measurements of CCr with omitted sign (absDCCr). Then, they were divided into 3 groups corresponding to the tertiles of absDCCr (tertile = 1/3). When the two values of CCr were compared among all patients, the mean difference between them (DCCr) was only 1.51 +/- 26.86 ml/min. The values of the individual DCCr varied, however, from -122.2. ml/min to 69.3 ml/min. As far as sex, age and height were concerned, there were no differences between the groups. However, weight was lower in group A (first tertile) vs. group B (second tertile) (p < 0.05). Also, BMI was lower in the group A vs. both group B and C (p < 0.05 and p < 0.01; respectively). In conclusion, our study points out to a poor reproducibility of the measurements of CCr in non-hospitalized subjects, especially in those with the high BMI.