Blood panels and screens
What a reference range is, and why yours may not apply to you
Normal is a statistical construction built from a reference population. If you do not resemble that population, the range is a rough guide at best.
The phrase normal range does a lot of quiet work on a lab report. It sounds like a statement about health. It is a statement about a sample of people who were measured once, somewhere, under conditions you were not told about.
The short version
- Reference intervals usually capture the central 95 percent of a defined reference population.
- Different laboratories using different platforms can publish different intervals for the same analyte.
- Age, sex, ancestry, altitude, pregnancy, and time of day all shift some intervals.
- Within-range does not mean optimal, and out-of-range does not mean diseased.
How an interval gets built
A laboratory recruits a group of people considered healthy, measures the analyte, and takes the central 95 percent of the resulting distribution. That range is then printed next to your result.
Every part of that process introduces assumptions. Who counted as healthy. How many people. Their age and sex distribution. Their ancestry. Whether they fasted. Whether the same analytical platform was used that ran your sample.
Why two labs disagree
Different immunoassay platforms can produce systematically different values for the same analyte in the same sample, which is why each publishes its own interval. Comparing a result from one lab against a range from another is a common and avoidable error.
This is also why serial monitoring should stay with one laboratory where possible. Your own trend is far more informative than your position in a range, and switching providers introduces a step change that has nothing to do with your biology.
Optimal ranges and where they come from
Consumer providers frequently print a narrower optimal range alongside the laboratory reference interval. Sometimes these come from outcome data in specific populations, which is legitimate. Sometimes they come from nowhere in particular, which is not.
If a provider shows you an optimal range, the reasonable question is what evidence defines it and in whom. A narrower band flags more people as suboptimal, and flagging more people is commercially useful.
Common questions
My result is just outside the range. Is that bad?
Usually it means repeat the test. Marginal values regress toward the mean on retesting far more often than they represent disease.
Should I use the optimal range instead?
Only if you can find out what it is based on. Ask the provider for the source.
Sources
- Biological age testing: what tests actually measure — https://ubiehealth.com/doctors-note/biological-age-testing-epigenetic-clock-guidance4262q2