Lab results include a reference range alongside each value — the range within which the majority of healthy people fall. Seeing a value outside that range can be alarming, but the reasons are often more nuanced than 'something is wrong'. Here's what to understand about reference ranges before drawing conclusions.
Where reference ranges come from
Most reference ranges are established by measuring the value in a large sample of apparently healthy individuals and taking the middle 95%. This means that 5% of healthy people will have a value outside the range even when they're perfectly well. A single mildly abnormal result in an otherwise healthy person is often not clinically significant. For a broader guide to interpreting lab results, see our blog post on making sense of your lab results and the in-app guide to reading lab results and insights.
Why ranges differ between labs
- Different analysers use different calibration — the same blood sample can produce slightly different numbers on different machines
- Reference populations differ — a range established in a European population may not perfectly reflect normal values in a Middle Eastern, South Asian or East Asian population
- Some labs use updated ranges from newer guidelines; others still use older values
- Altitude, temperature and sample handling all introduce small variations
How Looms handles multiple labs
When you have results from more than one lab for the same test, Looms plots all values on the same trend chart, displaying the reference range from each lab alongside the result. This means two data points from different labs may show different reference ranges even for the same test.
For trend analysis — watching whether a value is rising, falling or stable — the trend matters far more than whether any individual value falls just inside or outside the range.
When to act on an out-of-range result
- If the flag is marked CRITICAL — this means the lab has flagged a potentially life-threatening value and usually attempts to contact your doctor directly
- If the value is significantly outside the range, not just marginally so
- If the value is consistently out of range across multiple tests
- If the out-of-range value is accompanied by symptoms
- If a previously normal value has changed substantially