Extraction of human plasma or sera by heat treatment for a solid-phase radioimmunoassay of carcinoembryonic antigen.

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Abstract
Heat treatment and a solid-phase radioimmunoassay are combined to give a relatively simple and rapid procedure for assay of carcinoembryonic antigen in plasma or serum. The new way we describe to extract this antigen is an alternative to the conventional method of extraction with perchloric acid. Heating plasma or serum samples in acetate buffer (0.16 mol/L, pH 5.0) at 70 degrees C for 15 min precipitates out most of the heat-labile, nonspecific plasma proteins, but leaves most of the antigen in solution, with its immunochemical properties apparently unaffected. Comparison between the heat treatment and the perchloric acid extraction yielded comparable values when tested either by solid-phase radioimmunoassay or by the zirconyl phosphate precipitation method. An added advantage of our method is that it gives the same assay values for both plasma and serum. Results for a group of pathological plasma samples, assayed by both our method and the perchloric acid-zirconyl phosphate precipitation method, gave a correlation coefficient of 0.90.