A simple radioimmunoassay determination of urinary aldosterone using 125I-labeled ligand [ALDOCTK-125KIT] and its clinical application

Abstract

A method of radioimmunoassay for urinary aldosterone excretion (AER) using 125I-labeled ligand [ALDOCTK-125KIT] is described. The sensitivity, specificity, reproducibility and accuracy of this method were compared with the 3H-RIA method previously reported. Since the extraction method using ALDOCTK-125KIT was considered to be preferable to the direct method, the former method was applied to the present study. An excellent correlation was found between the values determined by the 3H-RIA method and the extraction method (r = 0.935, p less than 0.001, Y = 0.89X + 0.80, n = 146). The within-assay and the between-assay coefficient of variation was 7.7--15.0% and 9.7--12.2%, respectively. As a clinical application, the circadian variation of AER was investigated in 5 control subjects and groups of essential hypertension (EHT), primary aldosteronism (PA), chronic glomerulonephritis (CGN) and Cushing's syndrome, each of which consisted of 5 patients, all of which had serum creatinine concentrations of less than 1.2 mg/dl. Under a control diet containing 10 g of salt per day, urine was collected in 4-hour pools starting at 8:00 for the ensuing 24 hours, and AER was determined by means of both 3H-RIA and the extraction method. The difference of the values between the peak and the nadir in each subject was statistically significant, and marked and identical circadian variations of AER with the peak and the nadir at the period of 4:00 to 12:00 and 20:00 to 4:00 were observed in the control, EHT, PA and CGN groups. In the Cushing group, however, the circadian variation of AER was different from the other 4 groups: the peak and the nadir of AER occurred at the period of 20:00 to 24:00 and 4:00 to 8:00, respectively. The circadian variation of AER became more obvious in all groups including the Cushing, when each value was expressed in the percentage of the mean. AER under the control diet was 9.38 +/- 2.04 micrograms/day in the control subjects. In PA and CGN, AER was significantly higher, and in the Cushing group, it was significantly lower than that observed in the control. However, no difference was found in AER between the control and EHT. AERs in both 4-hour and 24-hour urine specimens measured by ALDOCTK-125KIT were consistent with those by the 3H-RIA method.