High sensitivity thyrotrophin assays in patients with severe non-thyroidal illnesses: a first-line screening test
Schutte, D.P.; Vermaak, W.J.; Zakolski, W.J.; Kalk, W.J.
Medical Laboratory Sciences 44(4): 312-319
1987
ISSN/ISBN: 0308-3616 PMID: 3141734 Document Number: 291562
We have evaluated the diagnostic utility of a single basal measurement of serum thyroid stimulating hormone (TSH), using two ultra-sensitive TSH assays, compared to those of a standard thyrotrophin releasing hormone (TRH) test and four estimates of free thyroxine, in 40 patients with severe non-thyroidal illnesses (NTI). Eleven uncomplicated hyperthyroid subjects and 20 normal controls were also studied. In the NTI group conventional thyroid function tests yielded a high proportion of values outside the reference ranges. Although a TSH response to i.v. TRH was detectable in all NTI patients it was sub-normal in 11, and the mean maximal rise (.DELTA. TSH) was 40% lower than in controls. Basal TSH concentrations were detectable in all NTI patients and controls using both ultra-sensitive assays.sbd.an immunoradiometric method (TSH-IR) and a fluoroimmunoassay (TSH-F). With the TSH-IR method all basal TSH values were within the normal range and clearly separated from the thyrotoxic values, which were all undetectable. Using the TSH-F method four patients with NTI had subnormal values and one thyrotoxic subject had a normal level. The .DELTA. TSH after TRH correlated with both basal ultrasensitive TSH measurements. We conclude that measurements of basal TSH levels using ultra-sensitive assays is likely to be useful as a first line screening test for thyroid disease, even in the presence of serious intercurrent non-thyroidal illnesses.