Thyroid function testing in primary care: overused and under-evidenced? A study examining which clinical features correspond to an abnormal thyroid function result.

BACKGROUND AND AIM: Diagnostic testing is increasing in primary care, including for thyroid disease. This study examined which clinical features were associated with an abnormal thyroid stimulating hormone (TSH) result.

DESIGN AND SETTING: This was a cross-sectional study in one general practice of 16,487 patients in Exeter, Devon, UK.

METHODS: We examined the primary care records relating to every TSH test taken in the year from August 2012, and extracted symptoms and/or the indication for testing. Associations with an abnormal result were tested using multivariable logistic regression. A cohort study was then performed of 100 patients newly recorded with each of the six features associated with an abnormal test result in the cross-sectional study, and the proportions tested for TSH and the results of that testing identified.

RESULTS: Two thousand thirty-five patients (12% of the practice population) had TSH testing in the year. Of these 35 (1.7%) had a TSH >4.5 mIU/l, suggesting hypothyroidism, and 7 (0.3%) had TSH <0.01 mIu/l suggesting hyperthyroidism. Features associated with an abnormal TSH were: pregnancy, odds ratio 41 (95% confidence interval 9.3-180), constipation 9.7 (2.1-45), palpitations 23 (3.4-150), hair loss, 21 (2.0-230), weight gain, 18 (1.6-190) and diarrhoea, 13 (1.2-130); in separate analyses only pregnancy and constipation were associated with a raised TSH, and the remaining four features with a low TSH.

CONCLUSION: The diagnostic yield of thyroid disease in this study was 2.1% suggests testing could be better targeted without missing diagnoses. The symptoms associated with thyroid disease differ from those generally reported. This may represent fewer patients presenting with advanced disease.