BACKGROUND: Immunoassays are used in almost all medical and surgical specialties, but they suffer from interference from proteins such as antibodies in some patients' sera. Such interferences are usually reported in the literature only as case reports after the introduction of a new assay. METHODS: We undertook a prospective observational study on 5310 patients for whom the common immunoassay tests for thyroid-stimulating hormone (TSH) and/or gonadotropins were requested. All TSH and gonadotropin results were critically assessed for a mismatch between the clinical details and analytical results to identify samples suspected of analytical unreliability. These were tested further by three approaches to screen for interference. RESULTS: From the 5310 sets of results, 59 patients' samples were identified as suspect and were tested further. Analytically incorrect results were found in 28 (0.53% of the total studied). The magnitude of interference varied, but in 23 of 28 patients (82%), it was considered large enough to have a potentially adverse effect on cost and/or the clinical care of these patients. Two cases, described in detail, illustrate the adverse effect of error on patient care and cost, and the second highlights the difficulties and limitations of current approaches for identifying interference and inaccuracy in immunoassays. CONCLUSIONS: Because millions of TSH/gonadotropin tests are carried out in UK hospital laboratories alone, our data suggest that thousands of patients could be adversely affected by errors from interferences. Early identification of interference in cases with unusual results could be valuable.
Ismail et al. (2002) studied this question.