Falsely elevated plasma aldosterone concentration by direct radioimmunoassay in chronic renal failure

Plasma aldosterone concentration (PAC) in patients with chronic renal failure was measured by radioimmunoassay with and without dichloromethane extraction before the assay. Blood samples were obtained from patients with chronic renal failure who were undergoing maintenance hemodialysis, from patients with chronic renal failure who were not undergoing hemodialysis, and from age-matched normal subjects. With the three radioimmunoassay kits tested, the direct assays without extraction in normal subjects gave PAC values comparable to those obtained after the dichloromethane extraction; in contrast, in patients with chronic renal failure, the direct plasma radioimmunoassays yielded consistently higher values than those obtained after the extraction (p less than 0.001). When various plasma steroid metabolite fractions were separated by high-pressure liquid chromatography (HPLC) with a reverse-phase column, and each fraction was assayed for PAC with the three radioimmunoassay kits, high immunoreactivities were found in the polar fractions in the plasma from patients with chronic renal failure but not in normal plasma. The ratios of the immunoreactivities of these polar fractions to that of the aldosterone fraction, determined after HPLC separation, showed a significant positive correlation (r = 0.746, p less than 0.001) with serum creatinine concentrations in plasma from patients with chronic renal failure who were not undergoing hemodialysis. These results indicate that the values for PAC are falsely elevated in chronic renal failure when PAC is measured by radioimmunoassay kits without prior extraction. Furthermore, plasma from patients with chronic renal failure contains a polar substance(s) that cross-reacts with antialdosterone antibodies. This so far-unidentified substance increases with advancing renal impairment.(ABSTRACT TRUNCATED AT 250 WORDS)