Panel guide
How to read a thyroid panel lab report
TSH is a common first-line thyroid marker reported by laboratories.
General biomarker education — not personalized medical advice. Learn more
What it measures
TSH (thyroid-stimulating hormone) is produced by the pituitary and is commonly used when evaluating thyroid status. Units are often mIU/L.
Why people track it
TSH may be ordered alone or with other thyroid tests. Confirmed historical values help structure appointment questions.
How to read your report
Reference intervals differ by assay. Confirm the extracted TSH and range against your original report before including it in history.
Important note
This is general information about laboratory markers. It is not a diagnosis, treatment plan, or personalized medical advice. Discuss your results with your clinician.
What’s on the report
A thyroid-related report may list TSH alone or TSH with free T4 and sometimes T3. Each line has a result, a unit, and that lab’s reference interval. Assay names can differ even when the abbreviation looks the same.
Line-by-line markers
How units work
TSH is commonly mIU/L (or µIU/mL). Free T4 is often ng/dL in the U.S. Other thyroid tests use different units. Do not compare a TSH of 2.0 to a free T4 of 2.0 — they are different tests.
What a flag means
Many reports mark a result with H, L, high, low, or an asterisk when it sits outside that laboratory’s printed reference interval. A flag is not a diagnosis. It means the value is outside the range on that report — discuss it with your clinician.
Why labs differ
Thyroid assays are not interchangeable. A TSH method at one laboratory can print a different range than another. If you change labs, bring both reports rather than assuming the numbers sit on the same scale.
How to compare over time
Medication timing, time of day, and illness can influence thyroid labs. When you save history, keep the collection time if it is printed and note whether thyroid medication instructions were followed.
Common questions
- What is TSH on a blood test?
- TSH is thyroid-stimulating hormone, produced by the pituitary. Laboratories report it as a concentration with an assay-specific range.
- Why is TSH ordered with free T4?
- The two tests answer different timing questions. TSH is often the screening line; free T4 adds context when a clinician wants both. Not every thyroid order includes both.
- Do I need to fast for a thyroid test?
- Thyroid tests usually do not require fasting. If they were drawn with a fasting lipid or metabolic panel, follow that order’s instructions.
- Why did my TSH range change between labs?
- Different assays use different reference intervals. Compare TSH to the range printed on that report, not to a range from another laboratory or a website.
- What does a flag on TSH mean?
- Many reports mark a result with H, L, high, low, or an asterisk when it sits outside that laboratory’s printed reference interval. A flag is not a diagnosis. It means the value is outside the range on that report — discuss it with your clinician.
- Can I compare thyroid labs from different years?
- Yes, as a history — especially if the laboratory method is similar. If the lab or assay changed, mention that when you ask your clinician about the trend.
- Does medication timing affect thyroid results?
- For people who take thyroid medication, clinicians sometimes give specific timing instructions before a draw. Follow those instructions and ask before changing how you take medication.
- Is a thyroid panel the same as a TSH-only test?
- Not always. Some orders are TSH only. Others add free T4, T3, or antibodies. Read the headings on your report rather than assuming a standard set.
Upload the report you just learned to read
Confirm extracted values against your source PDF. Charts use the range printed on that report.
See how it works →Questions for your clinician
- Does this TSH result suggest we should review free T4 or other thyroid tests?
- How does this TSH compare with my prior results?