FT3, FT4, TSH (ULTRASENSITIVE)

A FT3, FT4 and TSH blood test assesses thyroid function. TSH (pituitary hormone) controls thyroid hormone production; FT4 (free thyroxine) and FT3 (free triiodothyronine) are the active, unbound thyroid hormones. Together they diagnose and monitor hypo- or hyperthyroidism, guide treatment, and evaluate symptoms like fatigue, weight change, or palpitations. High TSH with low FT4 suggests hypothyroidism; low TSH with high FT4/FT3 suggests hyperthyroidism.

High free T3 (FT3) and free T4 (FT4) indicate hyperthyroidism, causing symptoms like weight loss, heat intolerance, tremor, palpitations, anxiety, increased appetite, sweating, diarrhea and menstrual changes. Common causes include Graves’ disease, toxic nodules, thyroiditis or excess hormone. Untreated, it can lead to atrial fibrillation, bone loss or thyroid storm. Prompt medical evaluation and treatment are important.

During pregnancy, trimester-specific TSH targets are used. Typical reference ranges are: first trimester about 0.1–2.5 mIU/L, second trimester about 0.2–3.0 mIU/L, and third trimester about 0.3–3.0 mIU/L. These can vary by lab; local pregnancy-specific reference ranges are preferred. Women on thyroid replacement are usually kept toward the lower end (roughly ≤2.5 mIU/L in the first trimester).

Costs vary by country and provider. Typical ranges: India ₹300–₹1,200; United States $40–$200 for a full FT3/FT4/TSH panel (prices lower with insurance or direct labs); United Kingdom private tests £20–£100 (NHS testing is free when ordered by a GP); Australia AUD $30–$120. Final cost depends on the lab, location and whether insurance or public health covers it.

No — fasting is not required for TSH, free T3, or free T4 tests. Morning sampling is preferred because TSH shows diurnal variation. If you take thyroid medication, delay the dose until after the blood draw per lab instructions. Also avoid biotin supplements and inform the lab about medications, recent iodine/contrast exposure, or other factors that can alter results.

Yes. Overt hypothyroidism can cause modest weight gain because a slower metabolism and increased fluid retention lead to fat accumulation and swelling. Typical gain is usually several kilograms rather than severe obesity. Proper diagnosis (TSH, free T4) and thyroid hormone replacement often stops further gain and may reduce some weight, but diet and exercise are usually needed for substantial weight loss.