Current Issues in Endocrine Testing

23 Jun 2022 15:30 16:00
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Current issues in endocrine testing

 

Leslie Charles Lai

Department of Endocrinology, Gleneagles Kuala Lumpur, Kuala Lumpur, Malaysia

 

Accuracy of hormone results is important in order for clinicians to correctly interpret biochemical results and diagnose endocrine disorders. Hormone assays are subject to assay variability, cross-reactivity, the hook effect, interference by substances such as heterophile antibodies, autoantibodies, macroprolactin, macro-TSH, biotin, to name a few. Certain hormones, for example ACTH and growth hormone, are rapidly broken down and the samples have to be handled appropriately, otherwise falsely low results will be obtained leading to erroneous diagnoses. Competitive immunoassays are most likely to have problems with cross-reactivity, whereas immunometric assays often have problems with heterophile antibodies. Dilutional linearity, spiked recovery, blocking heterophile antibodies, precipitation with polyethylene glycol, gel filtration chromatography and measurement using a different assay platform are techniques that can help in the evaluation of assay interference. Biotin, or vitamin B7, is consumed in supraphysiological proportions for common skin and hair conditions. When consumed in high doses, biotin interferes with the biotin-streptavidin system used in many immunoassays, resulting in falsely elevated levels in competitive immunoassays and falsely low levels in immunometric assays. For example, TSH can be falsely low and FT3 and FT4 can be falsely elevated due to biotin interference, resulting in a wrong diagnosis of hyperthyroidism. As hormone assays improve with better standardisation, cut-off levels for the diagnosis of certain hormone disorders need to be revised, for example, the 30-minute or 60-minute cortisol cut-off level used in the Short Synacthen Test for the diagnosis of cortisol deficiency/insufficiency.