Monitor thyroid levels: which tests, when to test, and simple tips

If you have thyroid disease or take thyroid medicine, tracking your thyroid levels makes treatment work better. This page shows the blood tests to ask for, when to schedule them, how to read the results, and small habits that keep labs accurate.

The basic tests are TSH, free T4, and sometimes free T3. TSH tells how the pituitary reacts to your thyroid. Free T4 shows how much main hormone is available. Free T3 is useful if symptoms don’t match TSH and T4. Add TPO (thyroid peroxidase) antibodies if autoimmune thyroid disease (for example Hashimoto’s) is suspected.

When to test and how often

Test 6–8 weeks after starting or changing a thyroid medicine dose. That gives your levels time to settle. Once your dose is stable and symptoms are controlled, test every 6–12 months. Test every 4–6 weeks during pregnancy or right after major dose changes. If you’re sick, rapidly changing weight, or taking new meds that affect thyroid function, test sooner.

Timing of the blood draw matters. Take levothyroxine consistently—usually first thing in the morning on an empty stomach. For reliable comparison, have your blood drawn at the same time of day and with the same gap after your pill. Avoid biotin for 48 hours before testing; it can skew some lab results.

How to read results and what to do next

A high TSH usually means underactive thyroid (hypothyroid); a low TSH suggests overactive thyroid (hyperthyroid). Normal ranges vary by lab, but common TSH ranges are roughly 0.4–4.0 mIU/L. Targets change by age, pregnancy, and the reason you’re treated. Don’t change medication from a single abnormal result—talk to your provider about trends, symptoms, and follow-up testing.

Subclinical results (mild TSH changes with normal free T4) often need watchful waiting and repeat testing. If symptoms persist while labs look normal, ask about free T3, antibodies, or other causes like vitamin deficiencies or mood issues. Always combine lab numbers with how you feel and medical history.

Practical tips: use the same lab for repeat tests, record results and dose changes in a simple log or app, separate levothyroxine from calcium or iron by four hours, and tell your provider about new meds, weight changes, or gastrointestinal problems that affect absorption. If you’re pregnant, older, or on combination T4/T3 therapy, monitoring will be closer and targets might differ.

If results and symptoms don’t match, ask for a clear plan: which test to repeat, how long to wait after a dose change, and when to expect improvement. Good monitoring is steady testing and small habits that make each number meaningful. Talk with your clinician to set targets that fit your age, pregnancy status, and overall health.