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

Abstract

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 thyroidstimulating 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. 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.

A Case With Immunoassay Interferences in the Measurement of Multiple Hormones

“…There are also a limited number of cases reported to have interferences for more than one hormone. Saleem et al (20) described a case with falsely low cortisol and falsely elevated fT4 in the same patient; however, ACTH, FSH, LH, PRL, IGF-1, PTH, T, and dehydroepiandrosterone sulfate levels were all normal in this case. Fiad et al (21) demonstrated simultaneous artifactual elevations in T 4 , T 3 , and TSH assays.…”

Ultra-Sensitive NT-proBNP Quantification for Early Detection of Risk Factors Leading to Heart Failure

“…Interference of endogenous substances in clinical samples result in the misinterpretation of a patient’s results leading to the wrong course of treatment [ 53 ]. It is reported that the serial dilution tests can verify the effect of interfering materials.…”

Steroid Assays in Paediatric Endocrinology

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