Endocrine Abstracts (2015) 39 CME5 | DOI: 10.1530/endoabs.39.CME5

Interpretation of dynamic tests

Jeremy Kirk

Birmingham, UK.

Whilst some hormones are secreted constantly, others have diurnal (eg. cortisol and androgens) and pulsatile (eg. growth hormone) secretion. As a consequence they require dynamic function tests to stimulate their production. It is worthwhile remembering that background data is not only limited but also often historical, going back over many decades. Often different units have different tests, assays & also cut-offs, which make comparison difficult. In a previous national audit there were 14 different protocols for the short hCG test, involving doses of hCG ranging from 500 – 15,000 iU. Whilst many units use a historical cutoff for GH-deficiency of ~ 6.7 μg/L, the most commonly used current GH assays have cutoffs ranging from 4.32 – 7.77 μg/L. Ideally each unit should set their own cutoffs, although in practice this rarely happens. There may also be considerable overlap between normal and abnormal eg. with pre-puberty and gonadotropin deficiency, and often the tests will need to be interpreted in the light of the clinical features and other supporting information. Each test can produce false negatives and also false positives, so the most important thing is proper selection of patient and also tests; you may not get the result you were expecting (or want!)

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