Furosemide test in stage III-chronic kidney disease and kidney transplant patients on tacrolimus

Furosemide test is a simple and useful test of renal physiology usually used for evaluating the capability of the collecting ducts to secrete potassium under the effect of this drug. Its behaviour pattern has already been established in healthy children, young, and old people, as well as in stage III-chronic kidney disease (III-CKD) patients. However, its behaviour has not been described in kidney transplant patients yet, which we explored in this study. Twenty young volunteers on a standard western diet (50 mmol of potassium/day) were studied: Ten were III-CKD and the rest were kidney transplant (KT) patients on FK. Before, while the test was being carried out, and 180 min after a single dose of intravenous furosemide (1 mg/kg), urine and blood samples were obtained, for creatinine and potassium levels. From these data, we calculated fractional excretion of potassium (FEK). Statistical analysis was performed applying Wilcoxon test. There was a significant difference regarding pre-furosemide (basal) FE of potassium between the III-CKD and KT groups 16 +/- A 5 (III-CKD) versus 7 +/- A 5 (KT), p = 0.008. Regarding the post-furosemide, peak FEK was significantly lower in the KT group (15 +/- A 11 %) compared to the III-CKD ones (49.8 +/- A 9 %, p = 0.01). In both groups, the peak FEK post-furosemide was reached later (120 min) compared to the conventional test (30 min). Furosemide test showed significantly lower basal and post-furosemide peak FEK values in KT patients on tacrolimus compared with stage III-chronic renal disease.