High TSH levels: what it means, symptoms and what to check next

• age 18+: 0.450 – 4.50 mIU/L
• age 18+, pregnancy: 0.100 – 4.00 mIU/L

Often reflects an underactive thyroid (hypothyroidism); medications and recovery from illness can also raise TSH.

Full reference table, citations and testing options: TSH biomarker page.

1. Primary hypothyroidism, most often autoimmune (Hashimoto's thyroiditis) — the thyroid itself is failing, so the pituitary pushes harder
2. Subclinical hypothyroidism — TSH mildly high (4.5–10 mIU/L) with a normal Free T4; a large share normalizes on repeat
3. Under-replacement on levothyroxine, or poor absorption — taken with food, coffee, calcium, iron or acid-reducers, or a missed-dose pattern
4. Recovery phase after a non-thyroidal illness, surgery or hospital stay — TSH overshoots for weeks on the way back to normal
5. Medications: lithium, amiodarone, immune checkpoint inhibitors, tyrosine kinase inhibitors, interferon; iodine excess (kelp, contrast dye) or iodine deficiency
6. After thyroid surgery or radioactive iodine, and in the recovery phase of postpartum, silent or subacute thyroiditis
7. Timing and body: TSH peaks in the early-morning hours and runs higher in a fasting morning draw; obesity and older age raise it modestly
8. Pregnancy, where the targets are stricter — first-trimester values above about 2.5 mIU/L are flagged and managed with the obstetrician
9. Rarely, a TSH-producing pituitary adenoma, thyroid hormone resistance, or an assay artifact (heterophile antibodies, 'macro-TSH') — suspected when Free T4 is normal or high and the picture doesn't fit

• Fatigue and sluggishness; needing more sleep
• Feeling cold when others don't
• Weight gain despite no change in habits, or difficulty losing weight
• Dry skin, hair thinning, brittle nails, constipation
• Low mood, slowed thinking, poor concentration ('brain fog')
• Heavier or irregular periods, difficulty conceiving
• Muscle aches and cramps, puffiness around the eyes, a hoarse voice, slow pulse
• Often none at all when the rise is mild — most subclinical results are found on routine blood work

• Free T4 (and Free T3) to see whether hormone levels are actually low — this is what separates overt from subclinical hypothyroidism
• TPO antibodies to look for Hashimoto's; positive antibodies make progression to overt hypothyroidism more likely (roughly 2–4% a year)
• Repeat TSH in 6–12 weeks, ideally at the same time of morning — a single mild elevation often normalizes
• Review of medications and supplements; levothyroxine timing (empty stomach, 30–60 minutes before food, 4 hours from calcium or iron)
• A lipid panel — high TSH raises LDL cholesterol, which falls once the thyroid is treated
• In pregnancy or when planning one, tell the obstetrician: the thresholds and the urgency are different
• A pituitary workup only when Free T4 is normal or high alongside the high TSH

Follow-up tests available at TestWell: Lipid Panel ($19.99), Thyroid Peroxidase (TPO) Antibodies Test ($25.49), Free T3 Test (Triiodothyronine) ($25.99), Calcium Test ($26.99), Free T4 Test (Thyroxine) ($20.99), T3 Uptake Test ($22.99).

If you take levothyroxine, recheck TSH about 6–8 weeks after any dose change — it takes that long for the level to settle — and then every 6–12 months once stable, per the American Thyroid Association. Without known thyroid disease there's no fixed interval; a repeat is reasonable when symptoms change or a first result was borderline.