Thyroid Function Tests: T3, T4 & TSH
Based on ATA and ICMR thyroid management guidelines
Educational content only. This information is for general awareness and does not constitute medical advice. Please consult a qualified healthcare provider for any medical concerns or before making health decisions.
The Role of the Thyroid Gland
The thyroid is a butterfly-shaped gland located at the front of the neck. It produces hormones — primarily thyroxine (T4) and triiodothyronine (T3) — that regulate the body's metabolic rate, heart function, digestion, muscle control, brain development, and bone maintenance.
The production of thyroid hormones is regulated by Thyroid-Stimulating Hormone (TSH), secreted by the pituitary gland in the brain. When thyroid hormone levels are low, the pituitary releases more TSH to stimulate the thyroid to produce more. When levels are sufficient, TSH production decreases.
Thyroid disorders are among the most common endocrine conditions globally, and India has a particularly high prevalence of iodine-deficiency-related thyroid disease. Women are significantly more likely to develop thyroid disorders than men.
Understanding Thyroid Function Tests
A thyroid function panel typically measures:
TSH (Thyroid-Stimulating Hormone):: The most sensitive initial test for thyroid function. An elevated TSH generally indicates the thyroid is underactive (hypothyroidism); a suppressed TSH may indicate overactivity (hyperthyroidism).
Free T4 (Free Thyroxine):: The main hormone produced by the thyroid. 'Free' T4 refers to the unbound, active fraction available to cells.
Free T3 (Free Triiodothyronine):: The more biologically active thyroid hormone. T4 is largely converted to T3 in the body's tissues.
Total T3 and Total T4:: Measure both bound and free hormone fractions. Used in specific clinical contexts alongside free hormone measurements.
Results must be interpreted alongside symptoms and clinical history by a qualified physician, as normal ranges can vary by laboratory and individual factors.
Who Should Get Thyroid Tests?
Thyroid function testing is commonly recommended for:
• Women over the age of 35, or at any age with symptoms
• Individuals with a family history of thyroid disease
• People experiencing unexplained weight changes, fatigue, or mood disturbances
• Women who are pregnant or planning a pregnancy
• Those with other autoimmune conditions
• Patients already diagnosed with thyroid disease, for ongoing monitoring
Common symptoms that may prompt thyroid evaluation include persistent fatigue, cold or heat intolerance, changes in heart rate, hair thinning, dry skin, and unexplained changes in weight — though these symptoms overlap with many other conditions and professional evaluation is essential.
Related Insights
Understanding Diabetes & Blood Sugar Tests
Learn how HbA1c, fasting glucose, and post-prandial tests help monitor and manage diabetes risk.
Preventive Health Screening: Your Annual Checklist
A full-body health check can catch silent conditions early. Here's what adults in India should screen for and why.