Sensitive thyrotrophin assays: excellent when properly used

Value of screening thyroid function in acute medical admissions to hospital

During a 4-month period an audit was performed to assess the value of thyroid function test (TFT) screening of all medical admissions, without known thyroid disease, to a single hospital. Abnormal TFTs were found in 125 of the 630 patients admitted (20%). Carbimazole or thyroxine was started in 13 patients (2.1%) discovered to have thyrotoxicosis (n = 4) or hypothyroidism (n = 9). In only four of these patients was the diagnosis of thyroid disease apparent clinically. The sick euthyroid state was found in 73 patients (11.6%), while the TSH compensated hypothyroid state was detected in 39 patients (6.2%). The low detection rate of new thyroid disease would suggest that unselective screening of all admissions is unjustified. However, the problem of diagnosing thyroid disease and the morbidity of untreated thyroid disease suggests that biochemical screening of TFTs in a selective group of medical patients admitted to hospital may be justified.

[Diagnostic significance of low thyrotropin in internal medicine]

In an attempt to determine the significance of low plasma thyrotropin (TSH) concentrations in internal medicine and the usefulness of systematic TSH assays in hospitals, 732 consecutive TSH measurements were performed in first-admission patients. TSH concentrations below 0.15 mU/l were found in 33 patients (4.5%) divided into 4 groups: a) in 5 patients a second assay made within 10 days of the first one showed no fall in TSH levels; b) 5 patients had known endocrine disease; c) in 8 patients hyperthyroidism could be asserted; the diagnosis had not been suspected in 3 elderly women and 1 pregnant women; d) 15 patients remained with low TSH concentrations but had normal free T3 and free T4 levels; in this group a goitre was detected in 7 patients and 8 had a severe chronic disease. These results showed that a TSH concentration below 0.15 mU/l corresponded to hyperthyroidism in less than one out of three patients in this population and that the 0.07 to 0.15 mU/l range is particularly misleading. A second TSH assay, free T3 and free T4 measurements ant thorough investigations in search of a goitre must be made. Severe organic diseases and several drugs may induce a fall in TSH. All considered, the 1% prevalence of hyperthyroidism in this population does not justify systematic TSH assays, but in subjects over 60 years of age, the clinical manifestations of hyperthyroidism may be misleading or unrecognized, and TSH assays should be widely performed.

The epidemiology of hypothyroidism--an update

Comparison of studies of the prevalence and incidence of hypothyroidism is hampered by differing definitions and population samples. Using a uniform set of diagnostic criteria, the prevalence of previously undiagnosed, spontaneous, overt hypothyroidism in community-based studies has been estimated between 2-4/1000 total population world-wide. If all cases of previously diagnosed hypothyroidism, previous thyroid surgery and radioiodine treatment are included, this prevalence rises to approximately 10/1000, and if subclinical cases are included, then the prevalence is probably over 50/1000 total population. The annual incidence of overt hypothyroidism is between 1-2/1000 for female and around 2/10,000 for males, with individuals having previously elevated TSH and positive circulating thyroid autoantibodies, being particularly at risk. The question of widespread population screening for hypothyroidism is unsettled, but it is probably not cost-effective unless incorporated as part of a screening programme for other conditions such as cervical cancer, or targeted at high risk groups such as post-menopausal women. The combination of serum TSH estimation and a high clinical index of suspicion should detect most patients with thyroid dysfunction, although detailed studies on the use of the more sensitive assays in the detection of both hyper- and hypothyroidism have yet to be published.