Specificity of sensitive assays of thyrotropin (TSH) used to screen for thyroid disease in hospitalized patients.

Abstract

Thyrotropin (TSH) concentrations were measured in 1580 hospitalized patients and 109 normal persons. Using the mean +/- 3 SD limits of the log values for the controls (0.35-6.7 milli-int. units/L), the proportion of abnormal TSH results in the hospitalized patients was 17.2%. TSH was undetectable (less than 0.1 milli-int. unit/L) in 3.1% of patients, suggesting hyperthyroidism, and high (greater than 20 milli-int. units/L) in 1.6%, suggesting hypothyroidism. On follow-up of 329 patients, 62% with abnormal TSH (less than 0.35 or greater than 6.7 milli-int. units/L) and 38% with normal TSH concentrations, only 24% of those with undetectable TSH had thyroid disease: 36% of them were being treated with glucocorticoids and 40% had nonthyroidal illness (NTI). Although half the patients with TSH greater than 20 milli-int. units/L had thyroid disease, 45% of patients had high TSH values associated with NTI. TSH concentrations usually returned towards normal when patients' therapy with glucocorticoids was discontinued or they recovered from NTI. TSH test sensitivity appeared good when the mean +/- 3 SD limits of the reference population were used, i.e., no cases of hyper- or hypothyroidism, as identified by free thyroxin index (FT4I), were missed. However, TSH test specificity was inferior to that of the FT4I test (90.7% vs 92.3%), although specificity could be improved to 97.0% if the wider TSH reference limits of 0.1 to 20 milli-int. units/L were used--limits considered pathological if applied to outpatients. Evidently, different reference intervals for TSH are needed for hospitalized and nonhospitalized patients. We conclude that a "sensitive TSH assay" is not a cost-effective thyroid screening test for hospitalized patients as compared with the FT4I.

The sick euthyroid syndrome: changes in thyroid hormone serum parameters and hormone metabolism

“…2). Other authors also reported a lower mean sTSH concentration in a group of NTT patients compared to normal (Boles et ul., 1987) and a higher incidence of suppressed sTSH values in NTI patients (Wehmann et al, 1985;Dubuis & Burger, 1986;Spencer et al, 1987;Ehrmann et al, 1989), but the total number of patients in thesc studies is much smaller. The patient selection in thcse latter studies was different from the previously mentioned series, for instance, patients receiving drugs known to suppress pituitary TSH secretion, such as corticosteroids (Faglia at al., 1973;Re et al, 1976) or dopamine (Besses et ul., 1975;Kaptein et al, 1980b), were not excluded from the study, nor were those with thyroid disease (Spencer et a/., 1987).…”

“…Furthermore, it seems that the rise in serum rT3 precedes the fall in T3 in mild rorms of illness. Serum TSH levels as measured with a second generation assay are usually normal in all groups, but may be reduced or elevated (Spencer et al, 1987;Krenning el d., 1987), while the TSH response to T R H may be blunted (Wartofsky & Burman, 1982). Spencer et 01.…”

“…cally employed doses (Spencer et a/., 1987). In chronic glucocorticoid therapy the effect on serum TSH normally subsides after several weeks, but the inhibitory effect of dopaminc pcrsists as long as the medication is used (Kaptein et a!., 1980a).…”

“…3 mU/1, Krenning et a/., Spencer, 1989) from thyrotoxic values. With the development of the second-generation immunoradiometric assays for TSH, with a 10 to 20-fold improvement in sensitivity (Spencer, 1988), these assays can reliably distinguish normal from hyperthyroid values (Spencer et al, 1987). Serum FT4 concentration T4 and T3 are present in the circulation either free or bound to TBG, TBPA or albumin, but according to the free hormone hypothesis, only the free hormones are physiologically active (Ekins, 1986;Mendel et al, 1988;.…”

Evaluation of serum basal thyrotrophin levels and thyrotrophin receptor antibody activities as prognostic markers for discontinuation of antithyroid drug treatment in patients with Graves' disease

“…Although the thyrotrophin-releasing hormone (TRH) stimulation test (Dahlberg et af., 1985;Schleusener et al, 1989) and the T3 suppression test (Alexander et al, 1970;Yamada et al, 1984) have been used widely used for the assessment of the pituitary-thyroid axis, these tests are not suitable for monitoring antithyroid drug treatment in daily practice. Since sensitive TSH measurements are able to distinguish suppressed serum TSH values from euthyroid levels (Klee & Hay, 1987;Spencer et al, 1987), the basal TSH measurement determined by the sensitive immunometric assay can replace the TRH stimulation or T3 suppression test and is more practically useful (Toft, 1988;Nicoloff & Spencer, 1990). Direct measurement of thyroid stimulating antibodies (TSAb) is very helpful for predicting the clinical outcome of Graves' disease (Zakarija e t al., 1980;Edan et al, 1989, Schleusener et a\., 1989.…”