Hormones & thyroid
Also known as Thyroid-stimulating hormone, Thyrotropin. Measured in mIU/L.
TSH is the signal the pituitary gland sends to instruct the thyroid to produce hormone, and it moves in the opposite direction to thyroid output. When the thyroid underperforms, the pituitary pushes harder and TSH rises; when the thyroid is overactive, TSH falls. This inverse relationship makes TSH the most sensitive single screening test for thyroid dysfunction, because the pituitary responds to small changes before thyroid hormone levels themselves leave the reference range. Its sensitivity is also its limitation. TSH describes the signal, not the hormone, so it cannot show whether T4 is being converted to the active T3 properly, whether an autoimmune process is underway, or whether conversion is being suppressed by illness or chronic stress. Those require free T4, free T3, reverse T3 and thyroid antibodies.
TSH measures the pituitary signal, not thyroid hormone, so it cannot show a conversion problem.
TSH follows a daily rhythm and is lowest in the late afternoon; consistent morning sampling makes results comparable.
Thyroid antibodies can turn positive years before TSH shifts, so autoimmune disease can precede any abnormal screen.
A raised TSH indicates the pituitary is working harder to stimulate an underperforming thyroid — hypothyroidism, or its subclinical form when thyroid hormones are still normal. Typical features are fatigue, cold intolerance, weight gain, constipation, dry skin and low mood. Autoimmune thyroiditis is the most common underlying cause and is identified with anti-TPO antibodies.
A low TSH suggests the pituitary is reducing stimulation because thyroid hormone is already plentiful — hyperthyroidism or its subclinical form. Features include palpitations, heat intolerance, weight loss, tremor, anxiety and disturbed sleep. It can also be caused by over-replacement in someone already taking thyroid medication.
| Band | Value |
|---|---|
| Typical laboratory reference range | 0.4 – 4.0 mIU/L |
| Range many clinicians treat as optimal | 0.5 – 2.5 mIU/LA clinical judgement, not a diagnostic threshold |
| Suggests hypothyroidism | > 4.0 mIU/LConfirm on a repeat sample with free T4 and anti-TPO |
| Suggests hyperthyroidism | < 0.4 mIU/L |
Laboratory intervals vary. Interpret with a physician.
Thyroid disorders, and autoimmune thyroiditis in particular, are common in India and disproportionately affect women. Iodine status, widespread iron and B12 deficiency, and high background rates of autoimmune thyroid disease all interact, which is a practical argument for reading TSH alongside ferritin and B12 rather than on its own — the fatigue being investigated frequently has more than one contributor.
Ferritin is the protein the body uses to store iron, and the amount circulating in blood is proportional to how much iron is held in reserve.
Vitamin B12 is required for red blood cell formation, DNA synthesis and the maintenance of the myelin sheath around nerves.
hs-CRP is a high-sensitivity measurement of C-reactive protein, a substance the liver releases in response to inflammation.
An abnormal TSH should always be confirmed on a repeat sample with free T4 before any conclusion is drawn, since TSH fluctuates with illness, sleep and time of day. Palpitations, significant unintentional weight change or a visible neck swelling need prompt medical assessment.
TSH measures the signal rather than the hormone. Free T4 and free T3 show what the thyroid is actually producing and converting, reverse T3 indicates whether conversion is being suppressed by stress or illness, and anti-TPO antibodies reveal an autoimmune process that can precede any TSH change by years. Those are the markers that explain a normal TSH with real symptoms.
Yes. TSH follows a daily rhythm, peaking overnight and reaching its lowest point in the late afternoon. The difference is enough to move a borderline result across a threshold, so consistent morning sampling makes results comparable over time.
A raised TSH with thyroid hormones still inside the reference range. Whether it warrants treatment depends on how high the TSH is, whether antibodies are present, symptoms, age and pregnancy plans. It is a clinical decision rather than something a number settles on its own.
The programme
Peak Brain draws a full blood and urine panel at your home, has a licensed physician read every marker together rather than one at a time, and turns what they find into a ranked 90-day protocol with a retest at the end.
Authorship & review
Written by the Peak Brain clinical team. Assigned clinical reviewer: Dr. Alfia Kaki, MD, PGC — review pending; this page has not yet been signed off.
Published . Last updated .
This page is general health information, not medical advice, diagnosis or treatment. Reference ranges vary between laboratories. Never delay or disregard advice from a qualified health professional because of something you read here. If you think you may have a medical emergency, call your local emergency number.