Is a value just outside the range a problem?

Usually not on its own. Small shifts are common and are read alongside your other results and your health history [WHO, 2011].

Why is my result different from a friend's normal?

Ranges depend on the lab, method, age and sex, so two normal values can look different. Compare against the range on your own report.

Do I need to understand every column?

No. Focus on the result, its unit, the reference interval, and any flag. The method and sample-type columns are background detail.

Should I bring the printed report to my doctor?

Yes. The full report, with its reference ranges and units, gives your doctor the complete context to read each value.

How to read a blood test report

To read a blood test report, look at each row across its columns, where each row is one test. The columns tell you the result, its unit, the range for that lab, and the method used. A flag marks anything that sits outside the range. The reference interval is the key to the whole report, not a single universal number.

Last reviewed: 2026-08-16

Illustration only — not a real report or a real laboratory

Example Diagnostic Laboratory (illustration)

Example report showing the test, result, unit, reference interval, method and flag columns
1Test	2Result	3Unit	4Biological Reference Interval	5Method	6Flag
Haemoglobin	10.8	g/dL	13.0–17.0	Photometry	L
Fasting Glucose	105	mg/dL	70–100	Hexokinase	H
TSH	2.4	µIU/mL	0.4–4.0	CLIA	—

1Test — the name of what was measured, one per row.
2Result — your measured value for that test.
3Unit — the scale of the value, such as grams per decilitre.
4Biological reference interval — the usual range for that lab.
5Method — the technique the lab used to measure the test.
6Flag — H for high or L for low, when the value is outside the range.

What are the columns on a lab report?

A report is a table. Each row is one test, such as haemoglobin or blood sugar.

Reading left to right, you usually see the test name, your result, the unit, the reference interval, and sometimes the method. A flag column marks anything outside the range.

Test name — what was measured.
Result — your value for that test.
Unit — the scale of the value, such as grams per decilitre.
Biological reference interval — the usual range for that lab.
Method — the technique the lab used.
Flag — H for high or L for low, when outside the range.

Which column matters most?

The reference interval matters most. It is the band of values seen in most healthy people, set on that lab's own machines.

Always compare your result with the range printed next to it, not with a number you found online [CLSI, 2010]. Ranges differ between labs.

What should you do with an out-of-range value?

Note which values are flagged and by how much. A flag means worth a closer look, not that something is wrong.

Bring the full report to your doctor. Your history, symptoms and other results turn a single number into useful information.

Frequently asked questions

Is a value just outside the range a problem?: Usually not on its own. Small shifts are common and are read alongside your other results and your health history [WHO, 2011].
Why is my result different from a friend's normal?: Ranges depend on the lab, method, age and sex, so two normal values can look different. Compare against the range on your own report.
Do I need to understand every column?: No. Focus on the result, its unit, the reference interval, and any flag. The method and sample-type columns are background detail.
Should I bring the printed report to my doctor?: Yes. The full report, with its reference ranges and units, gives your doctor the complete context to read each value.

Sources

CLSI (2010) — Clinical and Laboratory Standards Institute (reference intervals, methods, specimen handling)
WHO (2011) — WHO guidance on laboratory testing

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