Thyroid tests

Get to know TSH, T4 and T3, and how they appear together on a report.

Explore thyroid

TSH, free T4 and free T3: why the first number isn't a thyroid hormone

TSH is made by the pituitary, not the thyroid, and moves opposite to the hormones it controls. What each row measures, and why free and total are different tests.

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Test explainer

TSH

Reported in µIU/mL.

Test explainer

Total T3

Reported in ng/dL · nmol/L.

Test explainer

Total T4

Reported in µg/dL · nmol/L.

Test explainer

Free T3

Reported in pg/mL · pmol/L.

Test explainer

Free T4

Reported in ng/dL · pmol/L.

Reading the report

Guide

What the H and L flags on a lab report actually assert

A flag compares your number to the range printed beside it on that page — nothing more. What it does not tell you, and why healthy people collect them.

Guide

Why the same blood test has different "normal" ranges at different labs

Reference intervals are built from each lab's own population and equipment, which is why two labs can print different ranges for the same sample.

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