Is the reference interval the same as a target?

Not always. It is the usual range for healthy people. For some conditions your doctor may set a different personal target.

Why do age and sex change the interval?

Many values naturally differ by age and sex, so labs print separate ranges where that matters, such as for haemoglobin.

Can my own normal sit outside the interval?

Yes. A few healthy people always fall just outside the band, so a small step beyond it is often not a problem [CLSI, 2010].

Should I compare to an online range instead?

No. Compare with the interval on your own report, because it matches the lab and method that produced your result.

What does the biological reference interval mean?

The biological reference interval is the range of results seen in most healthy people for a test. Labs usually set it as the middle band that covers about 95 in every 100 healthy people [CLSI, 2010]. It is printed next to your result so you can compare the two.

Last reviewed: 2026-08-16

How is a reference interval set?

A lab measures a test in a large group of healthy people. It then takes the central band that most of them fall into [CLSI, 2010].

Because a few healthy people always sit just outside, a result a little beyond the range can still be normal for you.

Why does the interval depend on the lab?

Each lab uses its own machines, methods and local population to set the range. So the same test can have a slightly different interval at another lab.

This is why you should read the interval printed on your own report first.

Is a value outside the interval always a concern?

No. The interval is a guide, not a hard line between healthy and unwell.

Your doctor reads a value outside it alongside your symptoms, history and other results before drawing any conclusion.

Frequently asked questions

Is the reference interval the same as a target?: Not always. It is the usual range for healthy people. For some conditions your doctor may set a different personal target.
Why do age and sex change the interval?: Many values naturally differ by age and sex, so labs print separate ranges where that matters, such as for haemoglobin.
Can my own normal sit outside the interval?: Yes. A few healthy people always fall just outside the band, so a small step beyond it is often not a problem [CLSI, 2010].
Should I compare to an online range instead?: No. Compare with the interval on your own report, because it matches the lab and method that produced your result.

Sources

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

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