Triiodothyronine (T3) is one of the main thyroid hormones, along with thyroxine (T4).

T3 is more biologically active than T4 and regulates metabolic rate, heart function, digestion, and growth.

Clinical uses include:

Diagnosing hyperthyroidism (overactive thyroid).

Supporting evaluation of hypothyroidism (underactive thyroid).

Monitoring thyroid replacement therapy.

Assessing thyroid gland function in conjunction with T4 and TSH tests.

Often performed alongside TSH and Free T4 tests for a complete thyroid profile.

Analyte: Total Triiodothyronine (T3) in serum (ng/dL).

Normal Range (varies by lab): ~80–200 ng/dL.

Abnormal Findings:

High T3: Hyperthyroidism, Graves’ disease, thyroid nodules, excessive thyroid hormone therapy.

Low T3: Hypothyroidism, chronic illness, starvation, certain medications.

Clinical Use:

Provides a direct measure of thyroid hormone activity.

Helps guide diagnosis and management of thyroid disorders.

Supports endocrinology and internal medicine evaluation