My value changed labs but the flag did not. Why?

Each lab reads your value against its own range, so a similar value can flag the same way even if the numbers differ slightly.

Can I convert one lab's result to another?

For units you can convert the number, but the ranges still differ by method, so compare each result with its own printed range.

Which range should I trust?

Trust the range printed next to the result you are reading. It matches the method that produced that number [CLSI, 2010].

Do national bodies set one range for all?

For most tests, no single national range exists, so labs set their own. Where a body does publish thresholds, the test page names it.

Why do reference ranges differ between labs?

Reference ranges differ between labs because each lab sets its own range using its own machines, methods and local population [CLSI, 2010]. So the same test can have a slightly different normal band at two labs. This is why you compare your result with the range printed on your own report.

Last reviewed: 2026-08-16

What makes one lab's range different?

Three things mostly. The machine and method a lab uses, and the group of people it studied to set the range [CLSI, 2010].

Change any of these and the usual band can shift a little.

Does a different range mean one lab is wrong?

No. Each range is correct for that lab's own setup. Neither is wrong; they are simply matched to different methods.

That is why a value should be read against the range on the same report.

How should I compare results from two labs?

Compare each result with its own lab's range, rather than the raw numbers alone.

Where possible, use the same lab over time so the method and range stay the same.

Frequently asked questions

My value changed labs but the flag did not. Why?: Each lab reads your value against its own range, so a similar value can flag the same way even if the numbers differ slightly.
Can I convert one lab's result to another?: For units you can convert the number, but the ranges still differ by method, so compare each result with its own printed range.
Which range should I trust?: Trust the range printed next to the result you are reading. It matches the method that produced that number [CLSI, 2010].
Do national bodies set one range for all?: For most tests, no single national range exists, so labs set their own. Where a body does publish thresholds, the test page names it.

Sources

CLSI (2010) — Clinical and Laboratory Standards Institute (reference intervals, methods, specimen handling)

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