Is FT3 useful for Schlaf?

The question of whether FT3 (free triiodothyronine) is useful for sleep cannot be directly answered from the provided context. FT3 is a thyroid hormone that regulates metabolism. Thyroid dysfunction (hyper- or hypothyroidism) can affect sleep, but FT3 alone is not a standard biomarker for sleep disorders. Clinical guidelines typically recommend TSH, FT4, and possibly antibodies; FT3 is measured mainly when T3 hyperthyroidism is suspected or with certain medications. The evidence for FT3's independent utility in sleep issues is weak, based on mechanistic reasoning rather than robust human studies. A standalone FT3 test without other thyroid markers is not recommended for sleep assessment. Caveat: Always consult a physician for sleep disturbances before ordering hormone tests. Consumer lab tests have limited diagnostic value.