cAMP radioimmunoassay without interference from calcium or EDTA.

Calcium and EDTA interfere with radioimmunoassay of cAMP or acetylated cAMP. Both interferences with the assay of acetylated cAMP can be obviated by including in the buffer 15 mmol of CaCl2 per liter, which at the same time increases the affinity of the antibody by 89%. As a result, antibody can be decreased by 65%. This method requires no prepurification (extraction or chromatography), and no correction for analytical recovery is necessary. This assay can detect 12 fmol of cAMP per tube, so only microliter quantities of plasma are needed.