Please use this identifier to cite or link to this item: https://doi.org/10.1016/j.cca.2017.11.025
Title: A diagnostic curiosity of isolated androstenedione elevation due to autoantibodies against horseradish peroxidase label of the immunoassay
Authors: Lim, Yvonne Yijuan 
Ong, Lizhen
Loh, Tze Ping
Sethi, Sunil Kumar 
Sng, Andrew AJ 
Loke, Kah Yin
Halsall, David J
Hughes, Ieuan A
Lee, Yung Seng
Keywords: Science & Technology
Life Sciences & Biomedicine
Medical Laboratory Technology
Androstenedione
Autoantibodies
Erroneous
Horseradish peroxidase
Interference
Immunoassay
Spurious
Irregular analytical error
ANTIBODY INTERFERENCE
HETEROPHILE
DEFICIENCY
Issue Date: 1-Jan-2018
Publisher: ELSEVIER SCIENCE BV
Citation: Lim, Yvonne Yijuan, Ong, Lizhen, Loh, Tze Ping, Sethi, Sunil Kumar, Sng, Andrew AJ, Loke, Kah Yin, Halsall, David J, Hughes, Ieuan A, Lee, Yung Seng (2018-01-01). A diagnostic curiosity of isolated androstenedione elevation due to autoantibodies against horseradish peroxidase label of the immunoassay. CLINICA CHIMICA ACTA 476 : 103-106. ScholarBank@NUS Repository. https://doi.org/10.1016/j.cca.2017.11.025
Abstract: Two sisters with hirsutism presented with mild hirsutism and isolated, grossly elevated (> 34.9 nmol/L) serum concentrations of androstenedione measured by competitive, homogeneous immunoassay. The clinically discordant laboratory results prompted us to look for assay interference. In this immunoassay, horseradish peroxidase (HRP)-conjugated androstenedione competes with endogenous androstenedione for binding with the solid-phase polyclonal rabbit IgG antibodies. After a wash step, the amount of signal generated by the bound HRP conjugate is inversely proportional to the androstenedione concentration. Alternative analysis by tandem mass spectrometry (a good first line option for troubleshooting) and repeating the competitive immunoassay after polyethylene glycol treatment returned androstenedione concentrations within reference limits. These findings suggested that the original result was spuriously elevated due to assay interference. Additionally, the patient samples were pre-incubated with heterophile blocking reagents, normal rabbit IgG antibodies and HRP-conjugated normal goat IgG antibodies, followed by repeat measurement using the immunoassay. Only samples pre-incubated with HRP-conjugate returned significantly lower androstenedione (9.5 and 12.5 nmol/L, respectively), implying neutralisation of the interfering antibodies. Androstenedione remained grossly elevated in the other experiments. This deductive exercise showed that the interference is due to autoantibodies against the HRP label used in the immunoassay. Another immunoassay using HRP label (5α-dihydrotestosterone) also produced gross elevation that was normal by tandem mass spectrometry analysis. Assay interferences, though not uncommon, are frequently overlooked. Laboratory results discordant with clinical features should prompt consideration of assay interference to avoid unnecessary investigations and treatment. This is the first report of autoantibodies against the HRP label used in immunoassay.
Source Title: CLINICA CHIMICA ACTA
URI: https://scholarbank.nus.edu.sg/handle/10635/206174
ISSN: 00098981
18733492
DOI: 10.1016/j.cca.2017.11.025
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