Managing thyroid conditions in primary care

References

Summary

Schneider C, Feller M, Bauer DC, et al. Initial evaluation of thyroid dysfunction - Are simultaneous TSH and fT4 tests necessary? PLoS One 2018;13:e0196631.

This study based on analysis of cross-sectional data from Busselton (Western Australia) investigated whether testing TSH first, then assessing free T4 only if TSH is out of the reference range, would miss cases of hyperthyroidism or hypothyroidism. The alternative diagnostic scenario was to request both TSH and free T4 at the same time. It found that 93.0% of individuals had normal TSH and would not need further testing. Only 3.8% of individuals had a normal TSH and a free T4 outside the reference range and so would potentially be missed if testing is staggered rather than concurrent. However, in 85% of these cases, the free T4 was within 2 picomole/L of reference range limits, consistent with healthy outliers. This suggests that only about 0.57% of individuals with thyroid dysfunction would be missed by staggering TSH tests rather than measuring both TSH and free T4 at the same time.

The study did not support the simultaneous initial measurement of both TSH and T4.

LeFevre ML. Screening for thyroid dysfunction: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2015;162 (9):641-50.

Screening for thyroid dysfunction in non-pregnant people without clinical symptoms is not recommended by the US Preventive Services Task Force (USPSTF).

This guideline found:

• insufficient evidence to assess the balance of benefits and harms of screening for thyroid dysfunction
• insufficient evidence of benefit of screening for thyroid disease in reducing cardiovascular disease
• adequate evidence that in asymptomatic adults does not improve quality of life or meaningfully improve body mass index (BMI), blood pressure, bone mineral density or lipid levels
• adequate evidence that while screening can detect 'abnormal' serum TSH levels in asymptomatic persons, what constitutes an abnormal TSH level is uncertain. It noted that there is professional disagreement about the appropriate cut points for the lower and upper boundaries of normal TSH levels and accurate interpretation is further complicated by measurement variability and the sensitivity of TSH secretion to conditions other than thyroid dysfunction.

Croker EE, McGrath SA, Rowe CW. Thyroid disease: Using diagnostic tools effectively. Aust J Gen Pract 2021;50:16-21.

This article assists in identifying the appropriate sequence of investigations for thyroid disorders and identifies investigations with low diagnostic yield in certain clinical contexts.

This systematic review identified 27 studies conducted across UK/Europe, North America, Australia and new Zealand.  
Fourteen studies were conducted in a hospital setting and the remainder in primary care or community settings.

In most studies, the recommended testing strategy was based on TSH as a single first-line test for suspected thyroid dysfunction. Education, guidelines/protocols and audit and feedback were the most common types of interventions used. Reminders and decision tools were less commonly used, and changes to funding and evaluation of computer-based test requesting were used in few studies.

Single-mechanism interventions were effective in decreasing test volume or cost, changing patterns of TFT requesting, or improving compliance with guidelines. All but one of the multi-modal interventions were effective in decreasing volume of test requesting, changing the pattern of testing requesting, avoiding unnecessary testing or decreasing test-related expenditure.

Although interventions varied in terms of targeted audience, content, intensity, frequency and method of delivery, the authors suggested these differences had limited impact on reported effectiveness. Interventions that raise clinicians' awareness of existing guidelines, translate them into easy to follow rules and embed them in decision aids were considered a potentially effective combination.

Most of the studies were deemed of poor or moderate quality based on selection bias, lack of blinding and failure to control for confounders.

This Queensland study reported an increase in thyroid cancer incidence from 2.2 per 100,000 persons in 1982 to 10·6 per 100,000 in 2008. The largest rise was seen for incident papillary thyroid cancers suggesting overdiagnosis is a factor driving the increase in incidence. However, there was also an increase in the number of more advanced-stage cancers suggesting that other factors are also driving the increase. The authors of the study suggested that lifestyle and environmental factors such as increasing obesity or increased exposure to radiation may also be playing a role.

This US study using cancer registry data estimated that the proportion of incident papillary thyroid cancers attributable to overdiagnosis in 2011 was 5.5% and 45.5% in men ages 20–49 and 50 years or older, respectively. Among women aged 20-49, 41.1% of incident papillary thyroid cancers were attributable to overdiagnosis and in women 50 years or older, this rose to 60.1%. The authors estimated that overdiagnosis has resulted in an additional 82,000 incident papillary thyroid cancers that likely would never have caused any clinical symptoms.