Description

What This Test Measures

The Total T3 test measures the total amount of triiodothyronine (T3) in your blood, including both bound and free hormone. T3 is the active thyroid hormone responsible for regulating metabolism, energy production, heart rate, and body temperature.

Who Should Consider This Test

  • Fatigue or low energy
  • Unexplained weight changes
  • Rapid or irregular heartbeat
  • Anxiety or irritability
  • Heat intolerance or excessive sweating
  • Evaluation of suspected hyperthyroidism
  • Follow-up to abnormal TSH or T4 results

Why It Matters

T3 is the active form of thyroid hormone, and changes in Total T3 levels can help identify:

  • Hyperthyroidism (overactive thyroid)
  • T3 toxicosis (elevated T3 with normal T4)
  • Thyroid hormone conversion issues (T4 → T3)
  • Medication-related changes

This test is often used alongside TSH, Free T4, and Free T3 for a more complete thyroid evaluation.

Preparation

  • Fasting: Not required