What Do My Thyroid Numbers Actually Mean?
A thyroid report prints three numbers, and it is the pattern between them that has a name — not any single value. Enter your TSH, and Free T4 if you have it, to see which pattern yours fits. If you already take a thyroid tablet, it will also work out the exact time you should be taking it.
Printed as TSH, S. TSH or Thyroid Stimulating Hormone. Sometimes µIU/mL — it is the same number.
T4 is what tells a mildly raised TSH apart from a serious one. T3 mostly matters for an overactive thyroid.
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Enter your TSH to see which pattern your report fits. Add Free T4 as well and the answer gets considerably more precise — it is what separates a result that needs treating from one that usually just needs repeating.
Why the tablet so often stops working
Hypothyroidism is not a rare diagnosis in India. An eight-city study found it in roughly one adult in ten, and in 15.9% of women against 5.0% of men. What is less well known is how many treated patients are still out of range: in one Indian observational study, 54% of people on levothyroxine for at least two months still had an out-of-range TSH — and compliance did not explain it. They were taking the tablet.
The usual culprit is absorption. Levothyroxine only crosses the gut properly on an empty stomach, and it is bound up by calcium, iron, antacids, soy, fibre, and by tea and coffee. In a randomised study the identical dose produced a mean TSH of 1.06 mIU/L when taken fasting and 2.93 mIU/L when taken with breakfast. That gap is wide enough to look like an under-treated thyroid when the only thing wrong is the hour.
Which is the whole reason the timing planner above exists — and why a reminder that arrives at the right time, rather than just some time, is the version that changes the number on your next report.
Questions people ask
What is the normal range for TSH?
For a non-pregnant adult the range most commonly used is 0.4 to 4.0 mIU/L, the interval quoted by the American Thyroid Association. Indian labs vary — some print 0.35 to 5.5, some 0.27 to 4.2 — because the interval depends on the assay the lab runs. Where your own report prints a range, use that one; this tool lets you type it in. The unit is sometimes written µIU/mL, which is numerically identical to mIU/L.
What does a high TSH mean?
A high TSH means the pituitary is calling for more thyroid hormone than it is getting, which points to an underactive thyroid. What matters next is Free T4. High TSH with a low Free T4 is overt hypothyroidism and is normally treated. High TSH with a normal Free T4 is subclinical hypothyroidism, and in the 4 to 10 mIU/L band guidelines specifically advise against treating reflexively — it is often simply repeated first, because a recent illness can push TSH up temporarily.
Is a TSH of 5 or 6 high? Do I need medicine?
It is above the usual 4.0 cutoff, but on its own it rarely means starting tablets. With a normal Free T4 that is mild subclinical hypothyroidism, and the standard next step is to repeat the test in 6 to 12 weeks rather than treat immediately. Whether treatment helps depends on symptoms, anti-TPO antibodies, your age and whether you are pregnant or planning to be. Above 10 mIU/L the picture changes and treatment is usually recommended.
What is the normal TSH range in pregnancy?
This is the most confused number in Indian thyroid reporting. Older guidance set the first-trimester upper limit at 2.5 mIU/L, and many labs still print that. The 2017 American Thyroid Association guidance moved away from it, recommending a population-specific range or, failing that, the non-pregnant range with roughly 0.5 subtracted from the upper limit — which puts the first-trimester upper limit near 4.0. Indian data agrees, with one tertiary-centre study reporting 0.12 to 4.10 in the first trimester. The practical consequence is that a TSH of 3.2 in early pregnancy was once flagged as abnormal and now usually is not. Your obstetrician's target for you overrides any general range.
Do I need to fast for a thyroid test?
Fasting is not required for TSH itself, but the time of day genuinely matters. TSH follows a daily rhythm, peaking in the early hours and falling to its lowest in the afternoon — the same person can cross the 4.0 line depending only on when blood was drawn. Morning samples before 10 am are the convention. If you take levothyroxine, take that day's tablet after the blood draw, not before, or the T4 result reads artificially high.
What time should I take my thyroid tablet?
On an empty stomach, with plain water, either 30 to 60 minutes before breakfast or at bedtime at least three hours after your last meal. Both work; the bedtime option suits people who eat early or cannot hold off morning tea. What does not work is taking it with food. In a randomised study the same dose produced a mean TSH of 1.06 mIU/L taken fasting against 2.93 mIU/L taken with breakfast — a difference large enough to look like the dose is wrong when only the timing is.
Why is my TSH still high when I take the tablet every day?
Absorption, most often. Levothyroxine is bound up by calcium tablets, iron, multivitamins, antacids and acid-reducing medicines like pantoprazole, and by soy and high-fibre supplements — those need a four-hour gap, not a few minutes. Tea, coffee and milk also cut absorption, which is why plain water is specified. This matters in India in particular: 54% of treated Indian hypothyroid patients in one study had an out-of-range TSH, and it was not explained by whether they said they were taking their tablets. Bring it up before assuming the dose needs raising.
Can I take calcium or iron with my thyroid tablet?
Not at the same time. Both bind levothyroxine in the gut and stop it being absorbed. Leave at least four hours between them. The common pattern that goes wrong is a thyroid tablet at 7 am and a calcium tablet at breakfast an hour later — moving the calcium to the evening usually fixes it. This is worth checking with your doctor rather than rearranging tablets on your own.
What is the difference between T3, T4 and Free T3, Free T4?
T4 is the main hormone the thyroid releases and T3 is the more active form the body converts it into. 'Total' measures everything in the blood including the portion bound to proteins; 'Free' measures only the unbound fraction that can actually do something. Free T4 is the more useful of the two because protein levels shift in pregnancy and with oestrogen, which moves Total T4 without anything being wrong. If your report offers both, use the Free values.
Is this tool medical advice?
No. It matches your numbers to published reference intervals and names the pattern they fit, in the same way the range printed alongside your result does. It does not diagnose, and it will never suggest a dose — thyroid doses are adjusted in small steps by a doctor using a repeat TSH about 6 to 8 weeks later. Take the report itself to your doctor.