What this test measures
A thyroid profile is a conversation between two organs, printed as three or four numbers.
The pituitary gland in your head samples how much thyroid hormone is circulating and issues an instruction: TSH. When it senses too little, it raises TSH to push the thyroid harder. When it senses plenty, it lowers TSH. So TSH moves in the opposite direction to thyroid output, which is the single most confusing thing about the panel — a high TSH suggests an underactive thyroid, and a low TSH an overactive one.
T4 (thyroxine) is what the gland actually releases. T3 is the more potent form, and most of it is made not by the thyroid but inside your tissues by converting T4. Free T4 and free T3 measure the unbound, usable fraction; total T4 and total T3 include hormone stuck to carrier proteins, which is why they shift in pregnancy or on oestrogen-containing pills without anything being wrong with the gland.
Anti-TPO antibodies answer a different question altogether: not how the thyroid is performing, but whether the immune system is attacking it. In India, autoimmune thyroiditis is the commonest reason for an underactive thyroid, and iodine deficiency — historically the other major cause — has become much less common since salt iodisation.
The panel is built so that TSH does most of the work. It moves first and moves proportionally more than the hormones themselves, which makes it a sensitive early signal and, at the same time, an easy number to over-read.
What your result means
Read against the range printed on your own report. Indian laboratories commonly print upper TSH limits between 4.0 and 5.5 µIU/mL, and the assay your sample went through determines which.
TSH normal, T4 and T3 normal. Nothing further is usually needed unless symptoms point elsewhere.
TSH mildly raised, free T4 normal. This is subclinical hypothyroidism, and it is the commonest abnormal thyroid result by a wide margin. The gland is keeping output normal, but under more pressure. TSH is a restless number: it varies by up to a third across a single day, rises with fasting and with recent illness, and settles back into range on repeat testing in a meaningful proportion of people. This is a finding to confirm, not to act on immediately.
TSH raised, free T4 low. Overt hypothyroidism. The gland is no longer keeping up. This is a clearer picture and is assessed properly rather than watched.
TSH low, T4 or T3 raised. An overactive thyroid. Less common, but it needs assessment rather than reassurance, particularly with palpitations, weight loss or heat intolerance.
TSH low, T4 low. An unusual combination that points towards the pituitary rather than the thyroid, and is worth investigating rather than repeating.
Anti-TPO positive. Around one in ten adults carries these antibodies without any thyroid abnormality at all. Their value is predictive: a borderline TSH with positive antibodies is more likely to drift upward over years than one without.
Two further cautions. Any significant illness distorts thyroid tests for weeks afterwards, producing a pattern that mimics disease and resolves on its own. And biotin, present in many hair and skin supplements, interferes with several common thyroid assays and can make results look convincingly abnormal in both directions.
What each value means
Reference ranges differ between laboratories. Always read your result against the range printed on your own report.
TSH
Reference range
0.4 – 4 µIU/mL
- What it means
- Thyroid stimulating hormone, made by the pituitary. It is the instruction, not the product — it rises when the pituitary senses too little thyroid hormone and falls when it senses too much. Indian laboratories print upper limits anywhere from 4.0 to 5.5 µIU/mL depending on the assay, so read yours against your own report.
- Why it matters
- 6.2 with a normal free T4 is subclinical hypothyroidism — the pituitary is working slightly harder to keep output normal. TSH also swings with the time of day, with recent illness and between one blood draw and the next, so a single value in this band is a reason to recheck rather than a diagnosis.
- Next step
- Repeat after 6–12 weeks, drawn in the morning, together with free T4 and anti-TPO antibodies. The repeat value and the antibody status together carry far more information than the first number on its own.
Interpret in context. One result doesn't tell the whole story.
Free T4 (FT4)
0.8 – 1.8 ng/dL
The unbound, active fraction of thyroxine — the hormone actually available to your tissues. It is the number that separates a thyroid working harder to keep up (TSH raised, free T4 normal) from a thyroid falling behind (TSH raised, free T4 low).
Total T4
4.8 – 12.7 µg/dL
Thyroxine including the portion bound to carrier proteins. Because pregnancy, oestrogen-containing pills and some illnesses change carrier protein levels, total T4 can move without the active hormone changing at all.
Total T3
80 – 200 ng/dL
The more potent hormone, most of it converted from T4 inside your tissues rather than released by the gland. It stays normal until hypothyroidism is well established, which is why a normal T3 offers little reassurance on its own.
Anti-TPO antibodies
0 – 34 IU/mL
Antibodies against thyroid peroxidase, the marker of autoimmune thyroid disease (Hashimoto's). A positive result explains why a TSH is drifting and predicts whether it is likely to keep drifting. Cut-offs differ by assay — some laboratories use 34 IU/mL, others 60.
This is general education and cannot account for your history, your examination or your reports. If you need advice specific to your health, we’re always happy to see you in consultation.
What to do next
Confirm before concluding. A single borderline TSH is not a diagnosis. The usual approach is a repeat after six to twelve weeks, drawn in the morning, together with free T4 and anti-TPO antibodies if these were not part of the first panel.
Mention what you are taking. Biotin-containing supplements, oestrogen-containing pills, iron and calcium tablets, and steroids all affect either the result or its interpretation. Stopping biotin before a repeat sample is a conversation worth having with your doctor rather than a decision to make alone.
Read it against your symptoms honestly. Tiredness, weight gain and low mood are common with and without thyroid disease, and a mildly raised TSH is frequently blamed for symptoms it did not produce. Being clear about this protects you from years of dose adjustments that do not help.
Look at what travels with it. Thyroid disease clusters with other autoimmune conditions, and in women it is often found alongside irregular cycles, iron deficiency or a raised HbA1c. A first assessment usually includes more than the thyroid alone.
Ask about the plan, not just the number. Whether a borderline result is monitored or treated depends on the TSH level, antibody status, symptoms, age, cholesterol and whether pregnancy is being considered. That decision belongs with your doctor, with your whole picture in front of them.
This information is educational and not a diagnosis.
Alitheau Learning Sessions
Understanding Your Thyroid
- Why TSH moves in the opposite direction to thyroid output, and why that confuses everyone
- What free T4 adds that TSH alone cannot tell you
- Subclinical hypothyroidism: what it is, how often it settles on its own, and how it is usually approached
One result rarely tells the whole story
Have this read alongside everything else.
Conditions this result comes up in
Questions people ask
That pattern is called subclinical hypothyroidism. The gland is producing enough hormone, but the pituitary is pushing harder to get it. It is common, it fluctuates, and a proportion of people return to the normal range on a repeat test without anything being done. The usual approach is to recheck after six to twelve weeks with free T4 and anti-TPO antibodies before drawing any conclusion.
Not strictly, but the timing matters more than most people are told. TSH is highest in the early morning and falls through the day, and fasting samples read higher than fed ones. Drawing repeat tests at a similar time of morning makes them comparable.
Different assays measure slightly different things and carry different reference ranges. A change between laboratories is not reliable evidence of a change in you. Comparing trends within one laboratory is far more informative.
Yes. If you take thyroxine, taking it before the blood draw raises the measured T4 for several hours. Blood is usually drawn before the day's dose so the reading reflects your steady state. Discuss the timing with your doctor rather than changing anything yourself.