Health · Free tool
Thyroid Range (TSH/T3/T4)
TSH (Thyroid Stimulating Hormone) is the primary screening test. T3 and T4 are confirmatory. Pregnancy demands tighter TSH (< 2.5 in 1st trimester).
How thyroid screening works
TSH is the first-line test because the pituitary amplifies tiny changes in thyroid output. A TSH outside 0.4–4.5 mIU/L triggers a free T4 (FT4) and sometimes free T3 (FT3) to confirm whether the gland is under- or over-active. Indian labs often quote slightly tighter ranges (0.3–4.0) based on Indian Thyroid Society data, which we use here.
Worked example
A 34-year-old woman in Mumbai with TSH 6.8 mIU/L, FT4 1.0 ng/dL is subclinical hypothyroidism — TSH high but FT4 normal. Most endocrinologists treat with 25–50 mcg levothyroxine if TSH > 10, or if anti-TPO antibodies are positive. If she is pregnant, the first-trimester cap is TSH < 2.5 mIU/L, so even her current 6.8 would warrant immediate treatment to protect foetal brain development.
When to use this
- Routine annual lab report from Thyrocare, Dr Lal PathLabs, or SRL
- Pregnancy planning or any trimester (tighter cutoffs)
- Tracking dose changes after starting levothyroxine
- Hair fall, unexplained weight gain or fatigue prompting a TSH test
For related lab-report reads, try the vitamin D status and BMI calculator tools — many Indians flag positive on more than one.
FAQ
Subclinical hypothyroidism — should I treat?
TSH 4.5-10 with normal T3/T4 is "subclinical". Treatment debated — pregnancy planning and cardiovascular risk push for treatment; otherwise wait-and-watch with retest in 3-6 months.
My TSH is 0.5 but I feel hyper — concerning?
Anti-TPO and TSI antibodies might point to Graves' or thyroiditis. Get them tested if symptoms (palpitations, weight loss, anxiety) persist despite normal TSH.
Why is pregnancy TSH limit lower?
Higher demand on thyroid in pregnancy. Untreated hypothyroidism increases miscarriage and developmental delay risk. ATA recommends TSH < 2.5 first trimester, < 3 thereafter.