Thyroid- A TSH test is a blood test that measures this hormone. TSH levels that are too high low may be a sign of a thyroid problem, 4.0mU/L and above indicate hypothyroidism. Normal values of thyroxine (T4) and triiodothyronine (T3) The disorder is asymptomatic, and the diagnosis is made based on the results. heritability Studies have suggested that up to 67/of circulating thyroid hormone. Your thyroid is the metabolic powerhouse of the body and fasting can directly impact its function.