A specific radioimmunoassay for androstenedione with reduced bridge-binding.

Antibody used in a steroid radioimmunoassay raised against a steroid hapten-carrier protein conjugate may recognize both the hapten and the chemical bridge to the protein. Use of the same bridge in the radio-isotopic label may lead to higher affinity binding to the label than to the native steroid. Inhibition curves under these conditions are shallow and generally not acceptable for radioimmunoassay procedures. We have developed a radioimmunoassay for androstenedione that employs different bridges at the 11 beta position of the steroid for the protein conjugate and label. The resulting assay has greatly reduced bridge-binding, has an acceptable slope for the standard curve and is very specific as evidenced by low crossreactivies to other steroids.