Removal of heterophilic antibody interference in thyroid function tests with heterophilic blocking tubes
Annie Armston, Sarah Hyde & Linda Day
Heterophilic antibodies are human immunoglobulins with antigenic determinants directed against non-human species. These antibodies can interfere with the measurement of analytes in routine clinical laboratories, in particular in 2-site immunoassays. Skybio heterophilic blocking tubes-50 (HBT-50) are one way of overcoming this interference but, it has been reported (Sturgeon and Viljoen, Annals Clin Biochem, 2011, 48, 418), some samples may require two treatments to completely remove interfering antibodies. The aim of this study was to test this hypothesis in samples analysed in our laboratory for thyroid function. Between January to June 2011 samples from twenty five patients tested at UHS, which produced anomalous results for thyroid function, were included in this study. The results from these patients had one of the following abnormalities: raised FT4 with a TSH that was not suppressed, a low FT4 and normal TSH or a raised TSH with a high normal FT4. All samples went on to be treated for heterophilic antibodies with a Skybio HBT-50. If, after being treated with one tube, the results differed significantly from those obtained on the untreated sample, a second tube was employed. Of the 25 samples tested for FT4 and TSH after treatment with a HBT-50, 8 were significantly different from the original result. Two samples were insufficient but the remaining 6 underwent a second treatment and of these 4 had results that were significantly different from those obtained after the first tube. For two patients this would have resulted in a misclassification of the patient (subclinical hypothyroid) when in fact the patient had normal thyroid function. The double treatment with HBT-50 prevented unnecessary follow up of these patients. This study has demonstrated that treatment with one Skybio HBT is not always sufficient to remove all heterophilic antibody interference from a sample indicating a two-step protocol is necessary.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.