Endocrine
Hypothyroidism and hyperthyroidism: tests, treatment and monitoring
How TSH and free T4 separate primary from subclinical disease, how to start and monitor levothyroxine, and how to choose between the antithyroid drugs.
9 min read·core·
Reviewed by a licensed nurse · 25 October 2026
Reading the tests
| Picture | TSH | Free T4 | Meaning |
|---|---|---|---|
| Primary hypothyroidism | High | Low | Thyroid failure, often Hashimoto disease |
| Subclinical hypothyroidism | High | Normal | Treat on symptoms, a very high TSH, antibodies or pregnancy |
| Primary hyperthyroidism | Low | High (or high T3) | Graves disease, toxic nodule, thyroiditis |
| Subclinical hyperthyroidism | Low | Normal | Monitor, or treat in older adults or with cardiac risk |
| Central (pituitary) hypothyroidism | Low or normal | Low | Look for pituitary disease. TSH cannot be used to titrate. |
Managing hypothyroidism
- 01
Choose the starting dose
About 1.6 mcg/kg daily in a young healthy adult. Start at 25 to 50 mcg daily in older adults and anyone with coronary disease, and increase slowly.
- 02
Teach how to take it
Same time every day on an empty stomach with water. Separate from calcium, iron and antacids by about 4 hours.
- 03
Monitor
TSH 6 to 8 weeks after starting or changing the dose, then once the dose is stable every 6 to 12 months.
- 04
Adjust in pregnancy
Requirements often rise. Check TSH early and adjust, since untreated maternal hypothyroidism harms the fetus.
Managing hyperthyroidism
- ·Beta blocker (propranolol, atenolol) controls palpitations, tremor and anxiety while definitive treatment takes effect.
- ·Methimazole is the usual antithyroid drug. Propylthiouracil is used in the first trimester of pregnancy and in thyroid storm because it also blocks peripheral conversion, but it carries a liver injury warning.
- ·Radioactive iodine is an option for Graves disease or toxic nodules. It is contraindicated in pregnancy and breastfeeding.
- ·Both antithyroid drugs can cause agranulocytosis. Tell the patient to stop the drug and call at once for fever or sore throat.
Check yourself
Did it stick?
1. A 70-year-old with coronary artery disease has a TSH of 18 mIU/L and a low free T4. What starting levothyroxine plan is most appropriate?
2. A woman in her first trimester has Graves disease. Which drug is generally preferred?
3. A patient taking methimazole calls with fever and a sore throat. What is the best advice?
Sources
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Educational content for exam preparation. It is not clinical guidance and does not replace your facility's policies, current professional guidelines or the advice of a qualified clinician.