Research from M. Saleem and colleagues provide new insights into immunoassay
2009 MAY 26 - (NewsRx.com) -- According to a study from Christchurch, New Zealand, "Interference in immunoassays is a widely recognized problem, which could potentially lead to unnecessary investigations and treatment. We describe a case where interference in a cortisol immunoassay led to a falsely low serum cortisol concentration and interference in the free thyroxine assay led to falsely elevated serum thyroxine concentrations, in the same patient." "A 42-year-old woman with documented hypothyroidism underwent a synacthen test for suspected adrenal insufficiency. Previous thyroid function tests had been discordant and difficult to interpret, with elevated thyroxine and non-suppressed thyroid-stimulating hormone. The synacthen test showed a subnormal cortisol response and she was commenced on cortisol replacement. Clinically, it was doubted whether she had true adrenal insufficiency and it was thought that the cortisol results might be artefactually low due to assay interference. Cortisol was measured by an alternative immunoassay, before and after incubation in an antibody blocking tube ('Scantibodies'), after heat treatment and also after treatment with Protein A. The results supported assay interference and cortisol 'replacement' was stopped. Thyroxine had been discontinued although thyroid function tests (TFTs) were significantly different between analytical platforms, also consistent with interference. Thyroxine replacement was restarted and once on a stable dose, the discrepancy in TFTs was also investigated by similar procedures as for cortisol," wrote M. Saleem and colleagues. The researchers concluded: "Good clinician-laboratory interface and laboratory work-up of patients with results that are discordant from the clinical findings can reduce unnecessary investigation and inappropriate treatment." Saleem and colleagues published the results of their research in Annals of Clinical Biochemistry (A patient with pseudo-Addison's disease and falsely elevated thyroxine due to interference in serum cortisol and free thyroxine immunoassays by two different mechanisms. Annals of Clinical Biochemistry, 2009;46(Part 2):172-175). For additional information, contact C.M. Florkowski, Canterbury Health Laboratories, Corner Tuam St., Hagley Avenue, POB 151, Christchurch, New Zealand. The publisher of the journal Annals of Clinical Biochemistry can be contacted at: Royal Society Medicine Press Ltd., 1 Wimpole Street, London W1G 0AE, England. Keywords: New Zealand, Christchurch, Addison Disease, Adrenal Insufficiency, Biochemistry, Endocrinology, Hormones, Hypothyroidism, Immunoassay. This article was prepared by Life Science Weekly editors from staff and other reports. Copyright 2009, Life Science Weekly via NewsRx.com.
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