[Radioimmunoassay for plasma betamethasone and its application for clinical study (author's transl)].

A sensitive and specific radioimmunoassay for plasma betamethasone has been developed. The antiserum used was obtained by immunizing rabbits with betamethasone-3-oxime-human serum albumin (BM-3-oxime-HSA) conjugate. The sensitivity was 20 pg and a standard curve was established with a useful range from 20 pg to 4 ng. The cross reactivity of all tested endogenous steroids was less than 0.2%. Cortisol with a cross reactivity of 0.14% caused slight interference at very high concentrations, but this factor is negligible when plasma cortisol level is less than 30 microgram/dl. The calculated interference by cortisol was less than 10%, and plasma not receiving BM consistently gave blanks which were less than 20 pg/tube. Reliability criteria were satisfactory. By this method plasma BM could be measured directly in dichloromethane extract of plasma. The plasma concentrations of BM were measured in normal subjects and patients with liver diseases following oral administration of BM. The peaks of the plasma concentrations for 1.0 mg and 1.5 mg of BM were 345 +/- 40 (n = 3) and 710 +/- 200 ng/dl (n = 5) respectively within 2 hours after administration in normal subjects. After the peak level, plasma BM rapidly fell and disappeared 24 hours after administration in all examined normal subjects. In patients with chronic active hepatitis, the peak levels for 1.0 mg and 1.5 mg of BM were 428 +/- 48 (n = 4) and 837 +/- 83 ng/dl (n = 7) respectively within 2 hours after administration. However, the peak levels of plasma BM were higher than those of normal subjects, and the disappearance of BM from the blood was markedly delayed, reaching a level of 318 +/- 88 nad 622 +/- 148 ng/dl respectively for 1.0 mg and 1.5 mg of BM at 5 hours. The relatively high plasma concentration of BM, ranging from 135 to 170 ng/dl was maintained even 24 hours after administration in all patients with chronic active hepatitis. The disappearance of cortisol from the blood also rapidly fell in normal subjects, but was markedly delayed in patients with chronic active hepatitis. There was good correlation between the severity of the liver disease as measured by the ICG retention at fifteen minutes and removals of BM and cortisol from the blood.