Method-related interference in thyroid function assays

Methods

It is well documented that immunoassays, in general, are inherently vulnerable to different types of interference, including heterophilic antibody interference that has been known for decades. At present, immunoassays using fully automated platforms are the methods of choice in the clinical laboratory, especially for the measurement of analytes such as hormones that are present in the range of ng/L or less. In the past few years, many reports emerged worldwide emphasising the increased incidence of immunoassay interference in thyroid function assays, particularly in patients on biotin supplementation or in the presence of anti-streptavidin antibodies. Unfortunately, the frequency of such interference, its magnitude and the potential consequence of erroneous results that may significantly and adversely affect clinical management is rather difficult to assess.

As part of clinical authorisation, aberrant results which were not consistent with the clinical details (eg high FT4 in the thyrotoxic range associated with a normal or high TSH) were further investigated. Thyroid function tests (TFTs) are performed on the Roche Cobas 8000, using a chemiluminescence immunoassay that utilises biotin–streptavidin interaction in an immunometric sandwich reaction. 53 samples from 47 patients (34 female, 13 male, age range 4–91 years, mean+SD 49.5+26.8 years) with peculiar results that were not consistent with the clinical details were referred to another independent laboratory for analysis using a different method and platform (Siemens Advia Centaur XP) to exclude potential interference.