What Is TSH (Thyroid-Stimulating Hormone)?

What it is

TSH is a pituitary hormone that controls thyroid hormone production; it is the first-line thyroid function test.

Why it matters

Abnormal TSH indicates hypothyroidism (high TSH) or hyperthyroidism (low TSH).

Specimen

Whole blood / serum / plasma

Interpretation

High = hypothyroid; low = hyperthyroid (first-line thyroid test).

Limitations

Interpret with free T4 and clinical context.

Related test: TSH Rapid Test — specimen: WB / S / P