title: The effects of radioisotopes used in nuclear medicine on diagnostic radioimmunoassay testing. Is there any significant interference?
abstract: The administration of radioisotopes for diagnostic nuclear medicine scans and therapeutic procedures is quite prevalent today. A period of interference with the counting of a radioimmunoassay [RIA] test may occur with the serum of a patient receiving an in vivo radionuclide that decays by gamma emission. Because the logistics of precounting all specimens may be cumbersome and prohibitive, it is important to determine the degree of this interference. In this study, the authors evaluate the potential interference of the most commonly used radioisotopes with RIA studies. For two months (March and August 1988) 10,650 patient serum specimens were counted for significant background gamma radiation before RIA testing. Forty-three patients, on whom 105 RIA tests were performed, were identified as having preassay gamma radiation in their serum. With the use of selective energy windows for each different interfering radionuclide, proportional determinations were made as to the amount of interfering gamma radiation spilling into the iodine 125 test marker window. It was shown that initial whole serum pretest gamma counts as high as 111,000 counts/minute did not significantly affect the results of the RIA. Because of the meticulous washing and decanting procedures required in modern RIA and the monoclonal nature of most antibodies used currently, it appears the degree of nonspecific binding of this potentially interfering radiation is minuscule. The energy level of cobalt 57, however, and many of the other commonly used radioisotopes, overlaps so closely that it is difficult to window for this interference. It is possible, therefore, that this distinction cannot be made and folate and vitamin B12 test systems using cobalt 57 markers may have to be routinely prescreened. The authors conclude that the requirement for prescreening of all RIA test samples for interfering gamma radiation is unnecessary (1987 CAP Commission on Laboratory Accreditation Inspection Checklist, Section VII, Question 07.0290).
authors.affiliation: Department of Pathology, Geisinger Medical Center, Danville, Pennsylvania 17822.
authors.forename: J A
authors.initials: JA
authors.lastname: Riccio
authors.forename: D
authors.initials: D
authors.lastname: Maturani
authors.forename: J
authors.initials: J
authors.lastname: Wright
authors.forename: M K
authors.initials: MK
authors.lastname: Fleetwood
mesh_terms: D003947:Diagnostic Techniques, Radioisotope / Q000379:methods*; D006801:Humans; D009683:Nuclear Medicine / Q000379:methods*; D011863:Radioimmunoassay / Q000379:methods*; D011868:Radioisotopes
chemical_list: D011868:Radioisotopes