Alpha subunit contamination of human albumin preparations: interference in radioimmunoassy

Certain preparations of human serum albumin have been found to decrease the apparent titer of antisera to alpha subunit of human TSH (hTSH-alpha) and the sensitivity of the resultant radioimmunoassay for the immunologically common alpha subunit of the human glycoprotein hormones. Utilizing bovine serum albumin as the carrier protein, antisera to hTSH-alpha had 20-fold higher titers, and the resultant radioimmunoassay demonstrated 20-fold greater sensitivity for alpha subunit. Interference in the alpha immunoassay was not caused by protease since protease inhibitors did not eliminate it. Gel chromatography of human serum albumin revealed alph immunoactivity in an elution position identical to that of standard alpha subunit. Only certain human serum albumin preparations demonstrated interference in the radioimmunoassay because of the species specificity of the alpha subunit.A possible explanation for the alpha subunit contamination of human albumin preparations may be contamination of the serum source with placental blood, which contains large quantities of the alpha subunit of human chorionic gonadotropin.