High TSH: What It Means, Symptoms, and When to Act

Q: What does a high TSH mean?

A high TSH means your pituitary gland is producing more thyroid stimulating hormone than usual, which it does when it detects that circulating thyroid hormone is insufficient. TSH is the brain's signal to the thyroid to produce more hormone. High TSH = the signal is turned up, meaning the thyroid isn't producing enough. This is consistent with hypothyroidism, an underactive thyroid, of which Hashimoto's thyroiditis is the most common cause.

Q: What TSH level is considered high?

Most labs define the normal range as 0.4–4.0 or 0.4–4.5 mIU/L. TSH above 4.5 mIU/L is above normal, subclinical hypothyroidism if Free T4 is normal; overt hypothyroidism if Free T4 is also low. Many clinicians and patients report symptoms in the upper-normal range (2.5–4.5 mIU/L). The American Thyroid Association notes that many specialists prefer TSH below 2.5 mIU/L for symptomatic patients.

Q: What is Hashimoto's thyroiditis?

Hashimoto's is an autoimmune condition where the immune system attacks the thyroid gland, gradually reducing its hormone production. It's the most common cause of hypothyroidism in developed countries, responsible for around 90% of cases. It's diagnosed by elevated anti-TPO and/or anti-thyroglobulin antibodies on a blood test. These markers are routinely excluded from standard TSH panels, so if your TSH is elevated and you haven't been tested for antibodies, ask specifically.

Q: Can I have hypothyroid symptoms with a normal TSH?

Yes, in two ways. First, a TSH of 3.8 is technically normal but in the upper half of the range where many patients report symptoms. Second, TSH and Free T4 can both be normal while T4-to-T3 conversion is impaired, meaning Free T3 (the active form cells use) is low even when the other tests pass. A complete panel including Free T3 is needed to see this. Normal TSH alone does not rule out functional hypothyroidism.

Q: What does a full thyroid panel include?

A complete panel includes TSH, Free T4, Free T3, anti-TPO antibodies, and anti-thyroglobulin antibodies. Standard panels usually include only TSH, sometimes TSH + Free T4. Free T3 and antibodies require explicit request. If your GP has only run TSH and it's elevated or you're symptomatic, requesting the full panel is reasonable before any treatment decision.

Q: Does high TSH affect cholesterol?

Yes, hypothyroidism raises LDL cholesterol by impairing cholesterol clearance via LDL receptors in the liver. It also raises triglycerides. This is why NICE recommends ruling out hypothyroidism before starting cholesterol-lowering medication in patients with elevated LDL. If TSH is driving the cholesterol elevation, treating the thyroid normalises lipids without statins. If you have elevated LDL alongside elevated TSH, thyroid treatment comes first.

Q: What does high TSH with normal T4 and T3 mean?

This is subclinical hypothyroidism. TSH is above the reference range but free T4 and free T3 are still within normal limits. The pituitary is compensating, working harder than usual to maintain normal thyroid output. The normal T4 exists because of the elevated TSH signal, not despite a problem. Whether treatment is needed depends on how high TSH is, whether symptoms are present, and whether TPO antibodies are positive. Above 10 mIU/L, ATA and AACE recommend treatment regardless of symptoms. In the 4.5–10 range, the decision is individualised based on symptom burden, antibody status, and cardiovascular risk.

Q: Why is high TSH more common in women?

Three reasons. Hashimoto's thyroiditis, the most common cause of hypothyroidism, affects women at roughly 7–10 times the rate of men, with a global prevalence of 17.5% in women vs 6% in men (Frontiers in Public Health, 2022 meta-analysis). Postpartum thyroiditis affects around 7.5% of deliveries and causes a hypothyroid phase with elevated TSH at 4–8 months post-delivery; 20–40% of those cases progress to permanent hypothyroidism within 7 years. Third, perimenopause and hypothyroidism share almost identical symptoms, fatigue, weight gain, mood changes, sleep disruption, so thyroid dysfunction during this transition is frequently missed. 8–10% of perimenopausal women have thyroid dysfunction, and most are identified late.

TSH isn't a thyroid hormone, it's the signal your brain sends when thyroid output is falling short. A high result means the brain is compensating. Here's what that actually means for you.

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TSH range chart: low below 0.4, optimal 0.4 to 2.5, upper-normal 2.5 to 4.5, and high above 4.5 milli-international units per litre. — TSH zones — reference range 0.4–4.0 mIU/L (ATA), with many clinicians targeting 0.5–2.5. Above 4.5 suggests an underactive thyroid; below 0.4 suggests overactivity.

What TSH actually is, and why a high result means the thyroid is struggling

TSH is not a thyroid hormone. It's the pituitary's output, a signal that goes up when thyroid production is insufficient and down when the thyroid is overproducing.

4.5

mIU/L — upper limit of most lab normal ranges

Above 4.5 mIU/L with normal Free T4 is subclinical hypothyroidism. Above 4.5 with low Free T4 is overt hypothyroidism. But many patients report real symptoms in the 2.5–4.5 range, a zone labs classify as normal.

2.5

mIU/L, where many thyroid specialists prefer TSH for symptomatic patients

The American Thyroid Association notes that many specialists aim for TSH below 2.5 mIU/L in patients with symptoms, even when TSH is technically within the normal range. A result of 3.8 is "normal", but the upper half of normal — see how this "optimal vs normal" gap plays out across other markers too.

90%

Of hypothyroidism cases caused by Hashimoto's thyroiditis

Hashimoto's is the most common cause of elevated TSH. It's diagnosed by anti-TPO antibody testing, a marker routinely excluded from standard TSH panels. If your TSH is elevated and you haven't been tested for anti-TPO, ask specifically.

Here's the pituitary-thyroid feedback loop in plain terms: your pituitary gland constantly monitors circulating thyroid hormone (T4 and T3). When levels are sufficient, it keeps TSH low. When it detects the thyroid isn't producing enough, it turns up TSH, sending a stronger signal to the thyroid to produce more hormone. A high TSH is the pituitary's way of trying to compensate for an underperforming thyroid.

This means TSH is an indirect measure, it tells you what the brain thinks is happening, not what the thyroid is actually producing. This is why TSH alone is a screening tool, not a complete picture. You can have a TSH of 3.9 mIU/L (technically normal) while Free T4 is at the bottom of its range and Free T3 conversion is impaired, and feel every classic hypothyroid symptom without a single test coming back flagged.

The upper half of the normal TSH range (roughly 2.5–4.5 mIU/L) is where the most clinical disagreement sits. Labs classify it as normal. Many thyroid specialists don't treat it. But the patient experience documented in published research and in large community databases like those behind Hashimoto's forums consistently shows that a meaningful proportion of people with TSH in this zone have real fatigue, cold intolerance, and cognitive slowing that improves when TSH is brought lower.

What your TSH level actually means

The clinical zones, what each means for your thyroid, and what action is typically warranted.

TSH level (mIU/L)	Classification	Clinical picture	Status
Below 0.4	Low, suppressed	Suggests hyperthyroidism (overactive thyroid) or over-treatment with levothyroxine. Requires Free T4 and Free T3 to assess. Low TSH from hyperthyroidism has different implications than low TSH from over-treatment.	Investigate
0.4–2.5	Normal, optimal zone	Most people feel well in this range. The American Thyroid Association notes many specialists target below 2.5 for treated hypothyroid patients. No action needed if asymptomatic.	Optimal
2.5–4.5	Normal, upper zone	Technically within normal range but the symptomatic borderline zone. Fatigue, cold intolerance, brain fog, and weight gain are reported here. If symptoms are present, full thyroid panel (Free T4, Free T3, anti-TPO) is warranted to assess the complete picture.	Monitor if symptomatic
4.5–10	Subclinical hypothyroidism	TSH above normal with Free T4 still in range. Pituitary is compensating to maintain T4 output. Risk of progression to overt hypothyroidism, particularly with positive anti-TPO. Treatment decision depends on symptoms, antibody status, and cardiovascular risk.	Discuss treatment
Above 10	Overt hypothyroidism	Most guidelines recommend treatment at this level regardless of symptoms. Free T4 is typically low. Symptoms are usually present: fatigue, cold intolerance, weight gain, dry skin, constipation, low mood.	Treat

Labs normal but still exhausted?

A TSH of 3.8 passes on any standard blood test. So does a ferritin of 14, a vitamin D of 22, and a B12 of 195. All four can cause the same fatigue pattern. If your TSH is in the upper-normal zone and you're still exhausted, the full picture is worth investigating.

Read: Labs Normal, Still Tired? — the 6 markers standard panels miss

High TSH with normal T4 and T3: the subclinical zone

TSH above 4.5 mIU/L with free T4 and free T3 both in range is subclinical hypothyroidism. It affects 4–8.5% of adults without known thyroid disease and is the most common thyroid lab finding.

The normal T4 here is normal because TSH is elevated, the pituitary is compensating with a stronger signal to maintain output. Remove that elevated TSH signal and T4 would fall. A normal T4 alongside high TSH means the system is under strain, not that the thyroid is fine.

Trajectory depends mainly on antibody status. With positive TPO antibodies, progression to overt hypothyroidism runs at roughly 4–5% per year. With negative antibodies, many people stay stable for years or normalise spontaneously, particularly after an illness or acute stressor that transiently raised TSH.

Pattern	What it means	Next step
TSH 4.5–7, T4 normal, T3 normal	Mild subclinical hypothyroidism. Lowest-acuity pattern, but antibody status determines progression risk.	Add TPO antibodies. Retest TSH in 3–6 months.
TSH 7–10, T4 normal, T3 normal	Pituitary compensating significantly. Treatment decision depends on symptoms, antibodies, age, and cardiovascular risk.	Full panel. Discuss treatment if symptomatic or anti-TPO positive.
TSH above 10, T4 normal	ATA and AACE recommend treatment regardless of symptoms at this level. The normal T4 may not hold without intervention.	Discuss levothyroxine with your GP.

Same TSH, different trajectory

A TSH of 5.2 with normal T4 and negative anti-TPO is a different clinical situation from a TSH of 5.2 with positive anti-TPO. The numbers are identical; the prognosis is not. FixFirst analyses TSH alongside free T4, free T3, and TPO antibodies when they appear on the same panel, and flags the borderline values most labs mark green.

Upload your results to see the full picture

Symptoms of high TSH / underactive thyroid

Hypothyroid symptoms are non-specific, they overlap with iron deficiency, B12 deficiency, and depression. But some patterns are more thyroid-specific than others.

Fatigue and low energy

The most universal symptom, particularly marked in the morning. Thyroid hormone drives mitochondrial energy production; low output means cells run on reduced power across the board.

Cold intolerance

Feeling cold when others are comfortable, especially in the hands and feet. Thyroid hormone regulates metabolic rate and thermogenesis. One of the more specific hypothyroid symptoms when present alongside other signs.

Unexplained weight gain

Thyroid hormone governs basal metabolic rate. Low thyroid output slows metabolism, making weight gain easier and weight loss harder, even without dietary change. Typically modest (2–5 kg) in subclinical hypothyroidism.

Brain fog and slow thinking

Difficulty concentrating, slowed processing, and poor memory, sometimes described as "thinking through mud." Thyroid hormone drives neurological function directly, low levels slow processing, memory, and concentration.

Depression and low mood

Hypothyroidism and depression share overlapping symptoms and hypothyroidism can cause or worsen depression. Thyroid hormone regulates serotonin and dopamine pathways. Treating thyroid dysfunction first is warranted when TSH is elevated alongside mood symptoms.

Dry skin and hair thinning

The skin becomes dry, rough, and sometimes pale or yellowish (from carotene accumulation). Hair becomes coarse, brittle, and may fall out, particularly at the outer third of the eyebrows, which is considered a specific hypothyroid sign when present.

Constipation

Thyroid hormone stimulates gut motility. Low output slows intestinal movement, causing constipation that doesn't respond well to dietary changes alone. Often underrecognised as a thyroid symptom and attributed to diet or IBS.

Slow heart rate and high cholesterol

Thyroid hormone regulates heart rate and cholesterol metabolism. Hypothyroidism can cause bradycardia (slow heart rate) and elevated LDL cholesterol, which improves when thyroid function is restored. If LDL is elevated alongside high TSH, treating the thyroid may resolve both without targeting cholesterol directly.

Causes of high TSH in females

Three female-specific causes account for most of the sex gap. Each has a distinct trigger, timeline, and prognosis.

Hashimoto's thyroiditis

Global prevalence is 17.5% in women vs 6% in men (Frontiers in Public Health, 2022 systematic review of 8.4 million adults). The female-to-male ratio runs 7:1 to 10:1 across most study populations. Oestrogen upregulates B-cell activity, which is thought to lower the threshold for autoimmune attack on thyroid tissue. Hashimoto's is responsible for 90–95% of hypothyroidism in developed countries and is the most likely underlying cause of elevated TSH in a woman under 60. Hair thinning is often the first visible sign, and can occur even when TSH is still within the reference range. Blood tests for hair loss →

Postpartum thyroiditis

Affects approximately 7.5% of deliveries (ATA). During pregnancy, immune suppression protects the foetus; postpartum, the immune system rebounds. In susceptible women, particularly those with pre-existing TPO antibodies, this triggers thyroid inflammation. The typical sequence: a brief hyperthyroid phase (1–4 months post-delivery), then a hypothyroid phase with elevated TSH (4–8 months post-delivery). Most cases resolve by 18 months. But 20–40% develop permanent hypothyroidism within 7 years, so a TSH that normalises after delivery still warrants annual retesting.

Perimenopause overlap

8–10% of perimenopausal women have thyroid dysfunction; in women over 60 the figure reaches 14–20%. The diagnostic problem: fatigue, weight gain, mood changes, irregular cycles, and disturbed sleep are core features of both perimenopause and hypothyroidism. TSH that creeps up during this transition often goes undetected for years because the symptoms get attributed to "the change." Any woman presenting with these symptoms during the perimenopausal transition is worth testing with TSH plus free T4 before attributing the whole picture to hormonal change.

What a full thyroid panel looks like, and what to ask for

Standard panels often include only TSH. A complete picture requires more, and the additional tests change both diagnosis and treatment decisions.

TSH (Thyroid Stimulating Hormone)

Pituitary output, not a thyroid hormone

The standard screening test. High TSH signals insufficient thyroid hormone; low TSH signals excess. A good first-pass screen but insufficient on its own to understand what's actually happening in the thyroid.

✓ Included in standard panels

Free T4 (Free Thyroxine)

Main thyroid hormone, inactive form

The primary hormone secreted by the thyroid, circulating in its inactive form. Free T4 distinguishes subclinical from overt hypothyroidism. A normal Free T4 alongside elevated TSH = subclinical; low Free T4 alongside elevated TSH = overt.

✓ Often included with TSH

Free T3 (Free Triiodothyronine)

Active thyroid hormone, what cells actually use

T4 must be converted to T3 by the body before cells can use it. This conversion can be impaired, by illness, selenium deficiency, inflammation, or genetic variants, even when T4 is normal. A patient can have normal TSH and T4 but impaired T4-to-T3 conversion with real symptoms. Most standard panels skip this test.

Request specifically

Anti-TPO Antibodies

Primary Hashimoto's marker

Anti-thyroid peroxidase antibodies are elevated in around 90–95% of Hashimoto's thyroiditis cases. Positive anti-TPO with elevated TSH confirms autoimmune hypothyroidism and predicts progression, people with positive anti-TPO and subclinical hypothyroidism progress to overt hypothyroidism at 4–5% per year. Routinely excluded from standard panels.

Request specifically

Anti-Thyroglobulin (Anti-Tg) Antibodies

Second Hashimoto's marker

Elevated in around 60–80% of Hashimoto's patients. Worth running alongside anti-TPO because some patients are positive on anti-Tg only and would be missed by anti-TPO alone. Less commonly included but increasingly requested as awareness of Hashimoto's grows.

Request specifically

Thyroid Ultrasound

Imaging, not a blood test

Useful when antibodies are positive or when there is a palpable goitre or nodule. Ultrasound can confirm the heterogeneous, "moth-eaten" texture of Hashimoto's thyroiditis and assess for nodules. Not required for initial diagnosis but often ordered at the first endocrinology appointment.

Referred by GP/specialist

High TSH with no thyroid: post-thyroidectomy and post-ablation

After total thyroidectomy or radioiodine ablation, there is no thyroid tissue left. A high TSH means the levothyroxine dose is too low, not that new thyroid disease has developed.

Without a thyroid, TSH is entirely controlled by the levothyroxine dose. The pituitary is sensing insufficient hormone and sending a stronger signal to a gland that no longer exists. The action is a dose increase, not further thyroid investigation. Recheck TSH 6–8 weeks after any adjustment.

The TSH target depends on why the thyroid was removed. Benign disease calls for standard replacement. Thyroid cancer changes the target because residual cancer cells can be stimulated by TSH, guidelines recommend keeping TSH suppressed to varying degrees depending on cancer risk.

Reason for thyroidectomy	TSH target	Rationale
Benign disease (goitre, nodules, Graves')	0.5–2.0 mIU/L	Standard replacement. No reason to suppress TSH once cancer is excluded.
Low-risk differentiated thyroid cancer	<2 mIU/L	ATA 2015 guidelines. Mild suppression reduces recurrence risk without the side effects of aggressive suppression.
Intermediate/high-risk thyroid cancer	0.1–0.5 mIU/L	Stronger suppression to limit stimulation of any remaining cancer cells.
High-risk or recurrent thyroid cancer	<0.1 mIU/L	Full suppression. Long-term bone and cardiac effects require monitoring at this level.

If TSH keeps rising despite dose increases

Calcium supplements, iron supplements, and proton pump inhibitors (PPIs) all reduce levothyroxine absorption when taken within 4 hours of the dose. This is the most common cause of persistent TSH elevation despite adequate prescribing. Separating the dose from these by at least 4 hours, or switching to evening dosing, often resolves the issue without further dose increases. Coffee taken within 30 minutes of the morning dose reduces absorption by around 25% in some studies.

Post-thyroidectomy and pregnancy

Levothyroxine requirements increase during pregnancy, typically by 30–50%. Women post-thyroidectomy should have TSH checked as soon as a pregnancy is confirmed and retested every 4 weeks through the first trimester. The foetus relies entirely on maternal thyroid hormone during the first 10–12 weeks; delayed dose adjustment in this window affects foetal neurodevelopment.

What to do with a high TSH

The right next step depends on how high TSH is, whether symptoms are present, and what a full panel reveals. Here's the evidence-based path.

Get a full panel if you only have TSH

If your report shows TSH alone, which is the most common scenario, request Free T4, Free T3, anti-TPO, and anti-Tg antibodies before any other action. A TSH of 5.2 with normal Free T4 and negative anti-TPO is a different situation from a TSH of 5.2 with low Free T4 and strongly positive anti-TPO. You need the full picture to make the right decision.

If TSH is above 10: discuss treatment with your GP

Most published guidelines, American Thyroid Association, Endocrine Society, and NICE recommend treatment with levothyroxine when TSH is above 10 mIU/L, regardless of symptoms. The conversation with your GP should cover target TSH (typically 0.5–2.5 mIU/L for treated patients), the form of treatment (levothyroxine alone vs. combination T4+T3 in some cases), and retesting timeline (retest 6–8 weeks after starting treatment).

If TSH is 4.5–10: the decision depends on antibodies and symptoms

Subclinical hypothyroidism in this range is genuinely contested territory. Guidelines are inconsistent. The factors that generally push toward treatment: significant symptoms affecting quality of life; positive anti-TPO (predicts progression); pregnancy or intention to become pregnant (thyroid function during pregnancy has significant foetal implications); cardiovascular risk factors; age below 65. If you have all of these, treatment is reasonable. If asymptomatic with negative antibodies, watchful waiting with 6-month retesting is also defensible.

If TSH is 2.5–4.5 with symptoms, ask for a full panel and document your symptoms

This is the zone where most people get dismissed. Standard approach: bring a written symptom timeline to your GP, when symptoms started, which ones, severity, and impact on daily function. Ask for Free T4, Free T3, anti-TPO, and anti-Tg alongside a repeat TSH. If anti-TPO is positive and symptoms are consistent, some GPs will trial levothyroxine. If negative and Free T4 is mid-range, investigate other causes (ferritin, B12, vitamin D) before concluding it's thyroid-driven.

Rule out other causes of the same symptoms

The symptoms of mild hypothyroidism, fatigue, brain fog, hair loss, low mood, overlap completely with iron deficiency, B12 deficiency, vitamin D insufficiency, and sleep disorders. Before attributing everything to a TSH of 3.5, check ferritin, B12, folate, and vitamin D. Low ferritin alongside upper-normal TSH is a common combination that responds well to iron repletion alone, without any thyroid treatment. Fix the co-factors first and retest TSH, it sometimes normalises.

References & Guidelines

Note: Thyroid conditions are diagnosed and managed by a GP or endocrinologist using your full medical history alongside blood results. This guide covers the evidence around thresholds and what questions to raise, it is not a substitute for an in-person clinical assessment. If you have symptoms consistent with hypothyroidism, book an appointment rather than self-treating.

Frequently asked questions

What does a high TSH mean?

A high TSH means your pituitary gland is producing more thyroid stimulating hormone than usual, which it does when it detects that circulating thyroid hormone is insufficient. TSH is the brain's signal to the thyroid to produce more hormone. High TSH = the signal is turned up, meaning the thyroid isn't producing enough. This is consistent with hypothyroidism, an underactive thyroid, of which Hashimoto's thyroiditis is the most common cause.

What TSH level is considered high?

Most labs define the normal range as 0.4–4.0 or 0.4–4.5 mIU/L. TSH above 4.5 mIU/L is above normal, subclinical hypothyroidism if Free T4 is normal; overt hypothyroidism if Free T4 is also low. Many clinicians and patients report symptoms in the upper-normal range (2.5–4.5 mIU/L). The American Thyroid Association notes that many specialists prefer TSH below 2.5 mIU/L for symptomatic patients.

What is Hashimoto's thyroiditis?

Hashimoto's is an autoimmune condition where the immune system attacks the thyroid gland, gradually reducing its hormone production. It's the most common cause of hypothyroidism in developed countries, responsible for around 90% of cases. It's diagnosed by elevated anti-TPO and/or anti-thyroglobulin antibodies on a blood test. These markers are routinely excluded from standard TSH panels, so if your TSH is elevated and you haven't been tested for antibodies, ask specifically.

Can I have hypothyroid symptoms with a normal TSH?

Yes, in two ways. First, a TSH of 3.8 is technically normal but in the upper half of the range where many patients report symptoms. Second, TSH and Free T4 can both be normal while T4-to-T3 conversion is impaired, meaning Free T3 (the active form cells use) is low even when the other tests pass. A complete panel including Free T3 is needed to see this. Normal TSH alone does not rule out functional hypothyroidism.

What does a full thyroid panel include?

A complete panel includes TSH, Free T4, Free T3, anti-TPO antibodies, and anti-thyroglobulin antibodies. Standard panels usually include only TSH, sometimes TSH + Free T4. Free T3 and antibodies require explicit request. If your GP has only run TSH and it's elevated or you're symptomatic, requesting the full panel is reasonable before any treatment decision.

Does high TSH affect cholesterol?

Yes, hypothyroidism raises LDL cholesterol by impairing cholesterol clearance via LDL receptors in the liver. It also raises triglycerides. This is why NICE recommends ruling out hypothyroidism before starting cholesterol-lowering medication in patients with elevated LDL. If TSH is driving the cholesterol elevation, treating the thyroid normalises lipids without statins. If you have elevated LDL alongside elevated TSH, thyroid treatment comes first.

What does high TSH with normal T4 and T3 mean?

This is subclinical hypothyroidism. TSH is above the reference range but free T4 and free T3 are still within normal limits. The pituitary is compensating, working harder than usual to maintain normal thyroid output. The normal T4 exists because of the elevated TSH signal, not despite a problem. Whether treatment is needed depends on how high TSH is, whether symptoms are present, and whether TPO antibodies are positive. Above 10 mIU/L, ATA and AACE recommend treatment regardless of symptoms. In the 4.5–10 range, the decision is individualised based on symptom burden, antibody status, and cardiovascular risk.

Why is high TSH more common in women?

Three reasons. Hashimoto's thyroiditis, the most common cause of hypothyroidism, affects women at roughly 7–10 times the rate of men, with a global prevalence of 17.5% in women vs 6% in men (Frontiers in Public Health, 2022 meta-analysis). Postpartum thyroiditis affects around 7.5% of deliveries and causes a hypothyroid phase with elevated TSH at 4–8 months post-delivery; 20–40% of those cases progress to permanent hypothyroidism within 7 years. Third, perimenopause and hypothyroidism share almost identical symptoms, fatigue, weight gain, mood changes, sleep disruption, so thyroid dysfunction during this transition is frequently missed. 8–10% of perimenopausal women have thyroid dysfunction, and most are identified late.

What does high TSH mean if you have no thyroid?

After total thyroidectomy or radioiodine ablation, there is no thyroid tissue left. High TSH means the levothyroxine dose is too low, the pituitary is pushing harder because replacement hormone levels are insufficient. The fix is a dose increase, not further thyroid investigation. TSH target depends on the reason for thyroidectomy: 0.5–2.0 mIU/L for benign disease, below 2 mIU/L for low-risk thyroid cancer, and lower still for higher-risk cases. Recheck TSH 6–8 weeks after any dose adjustment. If TSH keeps rising despite increases, check whether calcium, iron, or PPI medications are being taken within 4 hours of the levothyroxine dose, all three reduce absorption.

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