The history and physical examination generally reveal the characteristic symptoms and physical signs that suggest hypothyroidism; however, laboratory evaluation is necessary to establish the diagnosis and cause of hypothyroidism.
Diagnostic lab tests include measuring the blood levels of:
- Thyroid stimulating hormone (TSH). This hormone will be elevated in cases of hypothyroidism. The TSH assay is the most sensitive test for the diagnosis of hypothyroidism.
- Free T4 (free thyroxine) and T3 thyroid hormones. Thyroid hormone levels in the blood will be low, but with mild, or "subclinical" hypothyroidism, the thyroid hormone levels can be in the low normal range.
- Thyroid autoantibodies (anti-thyroid peroxidase and antithyroglobulin autoantibodies). The presence of these antibodies indicates autoimmune thyroiditis (Hashimoto's disease) as the underlying cause of hypothyroidism.
Medically Reviewed by a Doctor on 12/5/2014
Stephanie L Lee, MD, PhD, FACE
Sonia Ananthakrishnan, MD
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