A reference range is the interval that contains the results of most people in a healthy reference group, usually the middle 95 percent. It is not a target, and it is not a diagnosis. The range on your report was produced by that lab's method and population, so it can differ from another lab's range for the same test.
Where the range comes from
A lab measures a group of people presumed healthy, orders their results, and takes the middle 95 percent. By construction, about five percent of healthy people fall outside, with roughly 2.5 percent at each end.
That has two consequences. A result outside the range is not rare. And a result inside the range does not prove anything is fine; it means the value is typical of the reference group.
Not every printed range works this way. Some are targets taken from guidelines, such as an LDL cholesterol goal or an HbA1c threshold used to define prediabetes. Those are risk thresholds dressed in the same column as a reference range, and they answer a different question.
Why two labs print different ranges
- Different methods. Two assays can produce slightly different values from the same sample.
- Different reference groups. Age, sex, pregnancy, and population change some ranges.
- Different units. mg/dL and mmol/L describe the same measurement in different numbers.
- Different targets. One lab prints a guideline target where another prints a population range.
- Different instruments and calibration. Even within one method, platforms differ.
This is why moving a single result from one lab to another is not a controlled comparison, and why a range copied from the internet is a guess about your report.
Normal is not the same as optimal
A value inside the range can still be worth watching. The range describes where most healthy people sit. It does not describe the lowest-risk level for every marker, and for some markers the two are not the same.
LDL cholesterol is the clearest example. A report may print a target below 100 mg/dL, while a person with a higher cardiovascular risk may be given a lower goal by their doctor. The printed number is a starting point, not a personal prescription.
The reverse is also true. A value just outside the range is common, and one reading is weak evidence of a problem. The lab flags it; a clinician decides what it means.
Why your own baseline carries more information
If your creatinine has sat at 0.8 for five years and is now 1.0, it may still be inside the lab's range, but the change is worth noticing. If your TSH has always run at 3.2 and is now 3.3, that is probably noise. A population range cannot see either pattern.
Three results over time, ideally from the same lab and under similar conditions, tell you more than one result compared with a stranger's range. This is the case for keeping your own history rather than only the latest report.
How to read the flag
- H or High. Above the lab's upper limit for that test.
- L or Low. Below the lab's lower limit.
- An asterisk. Often points to a comment or a note; read it before reacting.
- No flag. The result may be inside the range, or the lab may not flag that test. The two are not always the same.
What Doctano does with the range
Doctano keeps the range printed on each report, classifies the result against it as healthy, borderline, critical, or unknown, and shows the value next to the same marker from earlier reports. It does not replace a lab's range with a standard range from the internet.
A result without a usable numeric range stays unknown rather than being guessed. That is deliberate: a confident label on a result the app cannot evaluate would be worse than no label.
When to ask a person instead of a chart
A range cannot account for symptoms, pregnancy, medicines, recent illness, or a value that is critical. Those need a clinician. If a value is far outside the range, or you feel unwell, contact a doctor rather than reading further.