Variability of glomerular filtration rate estimation using single injection methods in Type 1 diabetic patients

Single-injection inulin clearance (SIIC) methods without urine collection have often been compared with classical constant-infusion inulin clearance methods. Therefore, we used repeated SIIC measurements to prove the hypothesis of a possible overestimation or variability of inulin clearance in Type 1 diabetic patients.

Two SIIC periods, glomerular filtration rate 1 and 2 (GFR 1, GFR 2) were performed consecutively on the same day. In diabetic patients, GFR 3 was measured several days later at the same time of day as the GFR 1 had been done. The calculation used a two-compartment modelling system (TCM) which showed excellent agreement to ratio of dose over area under the curve (D/AUC) calculation.

Twelve normotensive Type 1 diabetic patients (mean and SD), age 39 (10.7) years, diabetes duration 20 (10.7) years, HbA1c 8.5% (0.82%), albuminuria 13.8 (15.7) mg/24 h and six controls, age 26 (2.6) years were examined. Healthy controls showed an excellent repeatability between GFR 1 111.8 (11.44) and GFR 2 110.8 (11.41) ml.min-1.1.73 m2-1. However, in diabetic patients there was a highly significant decrease between GFR 1 129.4 (11.86) and GFR 2 118.1 (13.05) ml.min-1.1.73 m2-1. GFR 1 with 129.4 (11.86) ml.min-1.1.73 m2-1 did not differ significantly from GFR 3 with 129.9 (12.40) ml.min-1.1.73 m2-1 in diabetic patients (P < 0.839).

In contrast to normal subjects, in Type 1 diabetic patients single-injection inulin clearance technique showed a clinically relevant decrease in GFR on two repeated measurements on the same day. Overestimation of GFR by the first inulin clearance may be caused by incomplete inulin distribution in the slow compartment. Diabet. Med. 18, 464-468 (2001)