There is a number on the report, a range beside it, and in between sits the question of what it means for you. TSH 3.6 — within range. And yet you are cold all the time, your hair is thinning, and sleep does not touch the tiredness. Reading thyroid levels as a woman takes more than a chart: what matters is which values were measured at all, and how they sit in relation to each other.
In short: which thyroid values count, and what do they mean?
- TSH is the screening test. Typical is roughly 0.4 to 4.0 mU/L. High usually means underactive, low means overactive
- fT4 shows how much hormone is actually available and separates mild from pronounced dysfunction
- fT3 is the active form, but rarely needed for a first assessment
- TPO antibodies point to an autoimmune condition, usually Hashimoto's
- Raised TSH with normal fT4 is subclinical hypothyroidism and is rechecked first, not treated immediately
Reference ranges depend on laboratory and assay. Always compare your value against the range printed on your own report.
Topics in this article
The thyroid is a small organ with a long reach. It governs metabolic rate, body temperature, heart rate, digestion, cycle and mood. When it produces too little or too much, all of that shifts at once, and slowly. Which is exactly why it gets missed so often.
For women over 35 a second difficulty arrives: tiredness, weight changes, hair loss, feeling cold, low mood and cycle changes fit the thyroid and perimenopause equally well. Without lab work the two cannot be told apart. Where thyroid values sit in the bigger picture is covered in my overview of blood tests for women over 40.
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Which thyroid values get measured
Not every value needs measuring the first time round. Testing is built in stages, and sensibly so: each extra value without a concrete question mainly raises the odds of an incidental, unsettling result.
- TSH — the screening test TSH does not come from the thyroid but from the pituitary gland. It is the signal to produce more. If TSH rises, the body is short of thyroid hormone. If it falls, there is too much in circulation. Because TSH responds finely to small changes, it is the most sensitive entry point.
- fT4 — free thyroxine The storage form circulating in blood, converted into the active form as needed. "Free" means not bound to transport proteins, so genuinely available. fT4 decides whether a disturbance is mild or pronounced.
- fT3 — the active hormone The form that acts on cells. Usually unnecessary for a first assessment, useful mainly where an overactive thyroid is suspected or where the pattern is unusual.
- TPO antibodies Antibodies against the enzyme thyroid peroxidase. They are the key pointer to Hashimoto's thyroiditis, the most common cause of an underactive thyroid in iodine-sufficient regions.
- TRAb and Tg antibodies TRAb are measured where Graves' disease is suspected, so with an overactive thyroid. Tg antibodies matter mainly in follow-up after thyroid cancer. Neither belongs in a first screen.
- Ultrasound Not a blood value, but often the next step: it shows size, structure and nodules. It belongs with abnormal values or palpable changes in the neck.
Thyroid levels in women: chart of typical ranges
The ranges below are orientation values for adult, non-pregnant women. They do not replace the reference range on your own report. A review chapter in Endotext on thyroid function testing gives a usual TSH interval of roughly 0.4 to 4.0 mU/L while noting that free T4 results are method-dependent and therefore have to be read against assay-specific ranges.
- TSH · about 0.4–4.0 mU/L Above the range: a pointer to an underactive thyroid. Below it: a pointer to an overactive one. Under treatment, the lower half of the range is usually the target.
- fT4 · about 0.8–1.8 ng/dL (10–23 pmol/L) Normal alongside raised TSH suggests subclinical hypothyroidism. Low alongside raised TSH means overt hypothyroidism. The range differs noticeably between assays.
- fT3 · about 2.0–4.4 pg/mL (3.1–6.8 pmol/L) Relevant mainly with an overactive thyroid. An isolated low fT3 with otherwise unremarkable values often has other causes, such as acute illness or severe calorie restriction.
- TPO antibodies · usually below 34 IU/mL Positive means the immune system is attacking the thyroid. That is information about risk, not automatically an indication to treat. The height of the value says little about severity.
Two caveats matter. First, reference ranges vary between laboratories because different assays are used. Second, TSH swings considerably across the day: the same review chapter describes a circadian variation with an amplitude of around 50 percent and higher levels between 9 pm and 6 am. A sample taken in the late afternoon is therefore not directly comparable with a morning one.
What the combination means
Single numbers say little. What carries meaning is the pattern of TSH and fT4. These four constellations cover most results.
- TSH raised, fT4 normal — subclinical hypothyroidism The most common abnormal pattern in women. According to the StatPearls review on subclinical hypothyroidism, around 8 percent of women and 3 percent of men are affected. With a TSH below 10 mU/L the value is first rechecked after three to six months, because in almost half of cases it normalises on its own.
- TSH raised, fT4 low — overt hypothyroidism Here treatment with levothyroxine is generally indicated. A TSH above 10 mU/L is considered treatment-worthy regardless of fT4, as in many cases are symptoms, positive TPO antibodies or a wish to conceive.
- TSH low, fT4 or fT3 raised — overactive thyroid Typical signs are palpitations, restlessness, sweating, weight loss and disturbed sleep. This needs prompt assessment, not least because of the strain on heart and bone.
- TSH low, fT4 normal — subclinical hyperthyroidism Can arise from autonomous nodules, but also from an over-dosed thyroid hormone treatment. Either way it is worth following up rather than leaving the value alone.
Throughout: a single abnormal value is not a diagnosis. Before any treatment decision comes a second measurement, ideally with fT4 and TPO antibodies, and the fit with your symptoms.
Why women over 40 are affected more often
Thyroid disease is no coincidence in women. The StatPearls review on Hashimoto's thyroiditis gives a female-to-male ratio of at least 7:1 to 10:1, with most cases occurring between the ages of 45 and 55. TPO antibodies are detectable in over 90 percent of those affected.
That peak falls squarely into perimenopause. A paper in the Journal of Mid-Life Health states the core problem plainly: the signs of thyroid dysfunction resemble those of perimenopause closely enough to go unnoticed. In the group of perimenopausal women studied, around one in five had thyroid dysfunction. The authors therefore argue for measuring TSH generously, since the test is simple and inexpensive.
In practice: if you are already attributing your symptoms to menopause, that one extra value is worth it. Not because the thyroid is behind everything, but because it is one of the few causes that is clearly measurable and readily treatable. How hormonal symptoms otherwise overlap is covered in my article on perimenopause symptoms.
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What matters at the blood draw
A large share of confusing results comes not from the thyroid but from around the measurement.
- Go in the morning. Because of the circadian rhythm, TSH is lower in the morning than late in the evening. For follow-up what counts is measuring at a similar time each time.
- Pause biotin. High-dose biotin from hair and nail supplements can distort common assays in both directions. Most laboratories advise stopping it a few days beforehand. Ask the practice for the exact instruction.
- Separate levothyroxine in time. If you are already treated, the tablet is usually taken after the blood draw, otherwise fT4 comes back transiently raised.
- Do not measure during an infection. Acute illness shifts thyroid values temporarily, fT3 in particular. Waiting a week or two saves unnecessary worry.
- Plan the recheck. With a borderline TSH and no symptoms, repeating after three to six months is the standard route, not immediate treatment.
And take your results with you. With the thyroid the trend across years carries more meaning than any single measurement, precisely because Hashimoto's develops slowly.
What else influences the values
Thyroid values do not arise in a vacuum. Several factors shift them without the thyroid itself being diseased. Knowing them makes reading a report calmer.
Iron deficiency. Producing thyroid hormone requires an iron-containing enzyme. Low iron stores can impair the process and at the same time produce symptoms resembling an underactive thyroid: exhaustion, feeling cold, hair loss. Which is why measuring ferritin alongside is worthwhile.
Iodine and selenium. Both are building blocks of thyroid metabolism. Deficiency is unfavourable, and so is excess: high-dose iodine can trigger or worsen autoimmune thyroiditis. Iodine supplements belong in a medical conversation where Hashimoto's is known.
Severe calorie restriction and chronic stress. Under a sustained energy deficit the body downregulates conversion into the active form. That is an adaptation, not a disease, though it can show up in the lab as a low fT3. It typically appears with very strict diets combined with heavy training.
Medication. Besides biotin, lithium, amiodarone, corticosteroids and some cancer therapies affect thyroid function or its measurement. Absorption of levothyroxine is also disturbed, for instance by calcium and iron supplements or coffee taken shortly afterwards. Which is why the full medication list belongs in the conversation.
The FemBalance view: one value is not a trend
Two stories have settled around the thyroid. One says that as long as TSH is in range, everything is fine. The other says nearly every woman has a thyroid problem and you only need to measure closely enough. Both take the easy way out.
Katharina, 37, knows the first version: "I went to the doctor because I felt permanently exhausted. But my blood results were unremarkable. So at some point I thought maybe it was just me." The second version tends to end in five extra values, a report full of asterisks and even more uncertainty.
My position sits between the two and is unspectacular: measure the right values, measure them cleanly, and measure them again. A TSH of 3.8 is no cause for panic and no reason to close the file. It is a starting point that only becomes a statement alongside fT4, TPO antibodies and your symptoms. That calm around numbers is the difference between orientation and constant worry. It is how I work in my digital guides too.
The key takeaways at a glance:
TSH is the screening test, fT4 decides severity, TPO antibodies show the cause. fT3 does not belong in every first assessment.
Typical for TSH is roughly 0.4 to 4.0 mU/L, but reference ranges depend on laboratory and assay. The range on your report is the one that counts.
Raised TSH with normal fT4 is subclinical hypothyroidism. Below 10 mU/L it is usually rechecked first, because the value often normalises on its own.
Women are seven to ten times more likely to develop Hashimoto's, peaking between 45 and 55, right in the middle of perimenopause.
Measure in the morning, pause biotin beforehand, avoid testing during an infection, and keep a record of the trend.
Last updated: 7 September 2026
Frequently asked questions
What are normal thyroid levels in women?
As orientation, TSH runs roughly 0.4 to 4.0 mU/L, free T4 about 0.8 to 1.8 ng/dL and free T3 about 2.0 to 4.4 pg/mL. TPO antibodies are usually below 34 IU/mL. These ranges differ between laboratories depending on the assay, and pregnancy has its own limits. The reference range on your own report is what counts.
What does a TSH of 3.5 or 4 mean?
Both are still within range in most laboratories, but in the upper third. Without symptoms there is nothing to act on. If typical symptoms are present such as feeling cold, exhaustion, hair loss or constipation, it makes sense to add fT4 and TPO antibodies and recheck after a few months. A single value in the upper range does not on its own justify treatment.
Is TSH enough, or do I need fT3 and fT4?
For a first assessment TSH is generally enough, because it responds very sensitively. If TSH is abnormal, fT4 is added to distinguish mild from pronounced dysfunction. fT3 is useful mainly where an overactive thyroid is suspected or the pattern is unclear, and does not belong in every routine panel.
What do raised TPO antibodies mean?
They show the immune system is directed against the thyroid, which typically points to Hashimoto's thyroiditis. They are detectable in over 90 percent of those affected. Raised antibodies with a normal TSH are not a disease and not an indication to treat, but they do mean a higher risk of developing an underactive thyroid later. Regular TSH checks are the sensible response.
Can thyroid levels fluctuate in menopause?
Menopause itself does not directly change thyroid values. Thyroid disease does, however, cluster in exactly this stage of life, and the symptoms closely resemble each other. Which is why it makes sense to measure TSH once rather than attributing every symptom to perimenopause.
When should I go for a thyroid blood test?
Ideally in the morning, because TSH varies across the day and runs higher in the evening. For follow-up, always at a similar time. Pause high-dose biotin beforehand as instructed, take your tablet after the draw if you are already treated, and wait out acute infections.
This article is for general information and does not replace medical diagnosis or treatment. The ranges given are orientation values and do not apply to pregnancy, childhood or existing thyroid disease. Do not interpret results on your own, and never change existing thyroid medication yourself. With abnormal values or persistent symptoms, speak to a doctor.
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