Thyroid function tests before prescribing anti-dementia drugs: a retrospective observational study

Treatable causes of cognitive dysfunction, such as hypothyroidism, should be excluded by physicians before prescribing anti-dementia drugs. Many clinical guidelines for dementia recommend a thyroid function test (TFT) as one of the standard screening tests for cognitive dysfunction. This study aimed to investigate the national implementation rate of TFTs during the 365 days before the initiation of anti-dementia drugs.

In this retrospective observational study, using Japan's nationwide claim database, we enrolled ≥65-year-old patients who were newly prescribed anti-dementia drugs between April 2015 and March 2016. The outcome of this study was the implementation of TFTs in the 365 days prior to the index date. We used demographic data, including age, sex, comorbidities, home-based/institutional care, and provider type, as covariates.

We identified 262,279 patients newly prescribed anti-dementia drugs; of these, only 32.6% underwent TFTs before the initiation of anti-dementia drug treatment. Patients treated in dementia care centers were twice as likely to undergo TFTs as those treated in clinics (57% vs 26%; adjusted risk ratio: 2.17; 95% confidence interval: 2.01-2.33).

In Japan, patients with dementia often do not undergo TFTs before being prescribed anti-dementia drugs, particularly in a primary care setting. This suggests that the practice of screening treatable cognitive dysfunction should be audited.