Show Summary Details
Page of

Thyroid function tests and the effects of drugs 

Thyroid function tests and the effects of drugs
Chapter:
Thyroid function tests and the effects of drugs
Author(s):

Jim Stockigt

DOI:
10.1093/med/9780199235292.003.3031
Page of

PRINTED FROM OXFORD MEDICINE ONLINE (www.oxfordmedicine.com). © Oxford University Press, 2015. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy).

date: 10 December 2017

The assessment of thyroid function by laboratory testing began in about 1934 with the measurement of oxygen consumption or basal metabolic rate. Twenty years later measurement of protein-bound iodine became the standard technique and after a further 20 years this assay was superseded by radioimmunoassays of thyroxine (T4) and triiodothyronine (T3). Radioimmunoassays for thyroid-stimulating hormone (TSH) were reported from 1965, but early techniques could not distinguish normal values from the suppressed levels found in thyrotoxicosis. Until about 1990 this distinction was made by the administration of intravenous thyrotropin-releasing hormone (TRH), which fails to increase TSH to measurable levels in thyrotoxicosis, while producing a clear 5- to 15-fold increase in serum TSH in euthyroid subjects with normal pituitary function. Immunometric TSH assays now allow the suppressed serum TSH levels of thyrotoxicosis to be clearly distinguished from normal. This fundamental advance has coincided with the development of ingenious techniques to estimate the minute fraction of total serum T4 that circulates in the unbound state, but even the best free T4 methods offer only a marginal diagnostic advantage over the measurement of total T4, e.g. when the concentration of thyroxine-binding globulin (TBG) is abnormal. Current enthusiasm for free T4 and T3 estimation needs to be tempered by an understanding of the method-dependent limitations of these techniques, particularly in situations where assessment of thyroid function is most difficult (see below).

Access to the complete content on Oxford Medicine Online requires a subscription or purchase. Public users are able to search the site and view the abstracts for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can't find the answer there, please contact us.