Read this before the chart
A reference range is not a national standard. Each laboratory establishes its own, because it depends on the analyser, the reagent lot, the calibration, the measurement method and the population that laboratory serves. Two laboratories twenty minutes apart can print different ceilings for ferritin or TSH and both be right.
So this chart is a reading aid, not a verdict. The range that applies to you is the one printed on the same page as your value. If they disagree, your report wins — always.
Where a range comes from, and why healthy people are flagged
To set a range, a laboratory measures a group of healthy people — at least 120 of them for a given age, sex and method — and keeps the band where most of the results fall. The five people in every hundred who land outside that band are healthy too. They are simply at the edges.
That has a consequence nobody warns you about. Ask twenty questions of a healthy body and you will usually get at least one answer that looks wrong. It is more likely than not. The flag is doing its job: it says this value sits at the edge of what the laboratory measured, and nothing more.
A 2025 review in the Journal of the American Board of Family Medicine puts it plainly: the number of results falling outside the normal range far exceeds the number that are clinically meaningful, and minor variations labelled high or low cause patients unwarranted worry. The same review notes that laboratory results drive around 70% of clinical decisions — which is why the labelling matters so much.
Complete blood count
Adult values. Units vary by country: 10⁹/L and 10³/µL are the same figure, g/dL and g/L differ by a factor of ten.
Chemistry, liver, kidney
Where a target replaces a range — as it does for LDL cholesterol — the figure depends on your cardiovascular risk level and is set by your physician, not by the laboratory.
| Test | Usual range | Notes |
|---|---|---|
| Fasting glucose | 70 – 100 mg/dL · 3.9 – 5.5 mmol/L | Fasting only. 100–125 is the pre-diabetic band. |
| HbA1c | < 5.7 % | Three-month average. No fasting needed. |
| Creatinine | 0.7 – 1.3 mg/dL (m) · 0.6 – 1.1 (f) | Depends on muscle mass. Read with eGFR. |
| eGFR | > 90 mL/min/1.73 m² | An estimate from a formula, not a measurement. |
| ALT | 10 – 45 U/L | Read with AST and GGT, never alone. |
| TSH | 0.4 – 4.0 mIU/L | Follows a daily rhythm. Prefer a morning draw. |
| Ferritin | 30 – 400 µg/L (m) · 15 – 200 (f) | Rises with inflammation, which can mask a deficiency. |
| LDL cholesterol | target, not a range | Below 3.0 mmol/L for low risk; lower targets apply above it. |
What shifts a range
Sex changes several lines outright — haemoglobin, ferritin, creatinine. Age shifts others: children have their own ranges for almost everything, and eGFR declines slowly through adult life. Pregnancy has a separate set of ranges entirely, trimester by trimester.
Two more shifts are worth knowing because they are invisible on the report: laboratory method, which is why you should not compare across laboratories mid-follow-up, and time of day, which matters for TSH, iron and cortisol.
What a report could tell you, and usually does not
A value, a range and a letter leave you to do the hardest part yourself: deciding whether this matters. The family medicine review cited below argues that reports should go further and state the significance in plain terms — no immediate concern, worth raising at your next appointment, or contact your doctor now.
Almost no laboratory report does that today. Until they do, the work falls to you, and the useful questions are the ones this page keeps returning to: how far outside, in which direction, against which other lines, and compared with your own previous results.