DISCREPANCY BETWEEN LITHIUM AND FREE-WATER CLEARANCE IN PATIENTS WITHBARTTERS-SYNDROME

Lithium and free water clearance (C-Li and C-H2O) were measured simult aneously in 5 patients with Bartter's syndrome (BS), and the results w ere compared with values obtained in a large group of healthy control subjects. In line with the literature, fractional diluting segment rea bsorption estimated from C-H2O appeared to be subnormal in BS (82.4 +/ - 4.7 versus 89.4 +/- 4.4% in controls, p < 0.01). Fractional delivery to this segment, expressed as the maximum urine flow during water diu resis (V-max/glomerular filtration rate, GFR), also appeared to be red uced (11.3 +/- 1.6 versus 13.8 +/- 2.5%, p < 0.05), suggesting compens atory increased proximal reabsorption. In disagreement with the latter , C-Li/GFR, alleged to be a measure of fractional sodium and water out put from the proximal tubules, was increased (36.2 +/- 1.8 versus 30.7 +/- 5.1% in controls, p < 0.01), suggesting that suppressed proximal reabsorption could be the primary reabsorption defect in BS. During ch ronic converting enzyme inhibition with enalapril, given to treat hypo kalemia (3 patients), the concordance between the two methods was rest ored because C-Li/GFR fell by approximately 50%, whereas V-Max/GFR did not change; the alleged diluting segment rabsorption defect remained present. These contradictory results lead to the conclusion that one o f the two methods reflected the pattern of tubular sodium handling in BS incorrectly. However, the present study does not unequivocally indi cate which method yielded erroneous results in this condition.