Annals of Clinical Biochemistry > Volume 46, Number 2 > Pp. 172-175

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Saleem, M. Articles by Hale, P. Search for Related Content PubMed PubMed Citation Social Bookmarking                      What's this?

Case Reports

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

Mohamed Saleem¹, John G Lewis¹, Christopher M Florkowski¹, Guy P Mulligan², Peter M George¹ and Pamela Hale³

¹ Canterbury Health Laboratories, Corner of Tuam Street and Hagley Avenue, PO Box 151, Christchurch; ² Med Lab South, 137 Kilmore Street, PO Box 25091, Christchurch; ³ Department of Medicine, Nelson Hospital, Private Bag 18, Nelson, New Zealand

Corresponding author: A/Prof Christopher M Florkowski. Email: chris.florkowski{at}cdhb.govt.nz

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. 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.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				A A A Ismail Interference from endogenous antibodies in automated immunoassays: what laboratorians need to know J. Clin. Pathol., August 1, 2009; 62(8): 673 - 678. [Abstract] [Full Text] [PDF]