Artifactual Radioassay Results Due to Serum Contamination by Intravenous Radioisotope Administration: Falsely Low Serum Vitamin B12and Folic Acid Results

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Abstract
Carmel, Ralph: Artifactual radioassay results due to serum contamination by intravenous radioisotope administration. Falsely low serum vitamin Bl2 and folic acid results. Am J Clin Pathol 70: 364–367, 1978. Radioisotopic contamination by recent radiosotope administration (either99mtechnetium or67 gallium) to the patient for scanning purposes was found in 28 sera submitted for vitamin B12 or folic acid assay, or both, during the year prior to this study. In half the cases serum radioactivity was so great as to be readily identifiable during the assay. In the rest, however, the radioactivity would not have been detected had serum supernatant blanks not been routinely incorporated in the assay procedure. Many radio-assay kits make no provision for such supernatant control blanks. Were it not for these blanks, five patients would have been falsely identified as vitamin B12-deficient and three others as possibly deficient in the present series. Two of the five radio-active sera assayed for folate would also have given misleading results in the borderline-low range. The clinician should avoid ordering tests requiring radioassay when the patient has been given radioisotopes, and those performing radioassays must institute appropriate maneuvers to detect any such contamination.

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