Why one lab's range can differ from another's
If you have had thyroid tests at more than one lab, you may have noticed that the reference ranges don't match. That is normal, and it has a few ordinary causes.
Different equipment and methods
Labs use testing equipment from different manufacturers, and each method measures in a slightly different way. Each lab sets its ranges to suit the method it uses, so the range and the result belong together as a pair.
Different reference groups
A reference range is built from the results of a group of people. Labs and manufacturers don't all use the same group, so the edges of the range can shift a little from one lab to the next.
Different units
Labs in different countries often report the same test in different units. Free T4, for example, may appear in ng/dL on one report and pmol/L on another. The numbers and the ranges will look nothing alike, even for the same sample.
Ranges for particular groups
Some labs print separate ranges for certain groups, such as different age bands or stages of pregnancy. Your report should show which range was applied to you.
What this means for tracking
- Read each result against the range printed on that same report.
- Record the lab's name, the unit and the range every time, not only the result.
- If you have switched labs, tell your doctor. They can take that into account when comparing your results.
How thyro.health handles it
thyro.health stores every result with its own range and draws that range on the chart for that result, so a change of lab doesn't get lost. With thyro Premium, the "% through range" view shows where each result sat within its own lab's range, which lets you see results from different labs and units on one chart.
The app only records and displays. What your results mean is a question for your doctor.
This article is for general information only and is not medical advice. Always talk to your doctor about your own results and treatment.