Rapid diagnosis of thyroid disease using carbonic-anhydrase immunoassay

Erythrocyte carbonic-anhydrase-I (C.A.I.) concentration was measured by radial immunodiffusion in 30 thyrotoxic patients and 15 myxoedemic patients, the results being compared with those found in a control group of 90 euthyroid individuals. In thyrotoxicosis the erythrocyte-C.A.I. concentration was found to be below 10-29 mg/g haemoglobin, whereas the normal range varied from 11-1 to 22-5 mg C.A.I./g Hb. Low values were found in 4 patients with triiodothyronine(T3)-toxicosis. In myxoedema, the mean erythrocyte-C.A.I. concentration, though elevated at 20-37 mg/g Hb, fell within the normal range. In pregnancy, the erythrocyte-C.A.I. concentration rose with time, the mean value at tern being 20-6 +/-S.D. 3-3 mg/g Hb. In a group of women taking oral contraceptives, a low erythrocyte-C.A.I. concentration was noted--an effect which was most obvious among those taking low-oestrogen contraceptives. It is suggested that erythrocyte-C.A.I. estimation provdes a rapid screening test for thyrotoxicosis.