Every week, I review the latest sports nutrition research, looking beyond the headlines to understand what the findings actually mean for athletes. This week, a new perspective article looks at why standard blood test reference ranges don't always tell the whole story for athletes.
The study
This is a perspective article, rather than a new clinical trial. It looked at why standard blood test results can be difficult to interpret in athletes.
When you get bloodwork done, your results are usually compared with a range based on the general population. Around 95% of healthy people fall within this range.
But athletes aren't the general population.
Training can affect blood markers, and a result that looks unusual might be perfectly normal for someone who trains regularly. Likewise, a result marked as normal doesn't always mean an athlete is getting everything they need, especially if not eating enough.
The author looks at five areas where standard blood test ranges may not tell the whole story:
- Iron
- Vitamin D
- Zinc
- Hydration
- Energy availability
The results
The author argues that athletes need more than a simple normal-or-abnormal reading. He proposes looking at blood results through three layers:
- Population reference range: Is the result unusual compared with the general population?
- Purpose-specific thresholds: Is the result low enough to indicate a nutritional insufficiency or potential health risk?
- Individual baseline: How does the result compare with the athlete's own previous measurements?
The third layer is particularly interesting. The author calls it a "nutritional passport," drawing on the Athlete Biological Passport used in anti-doping to track changes in an athlete's individual blood markers over time.
He also recommends four practical safeguards:
- Standardize blood collection conditions so results can be compared reliably.
- Test when there is a specific reason, rather than ordering panels without a clear purpose.
- Avoid unnecessary supplementation based on a single result.
- Don't confuse what's usual in athletes with what's nutritionally sufficient.
Why it matters
Athletes can have blood results that look unusual because of normal training adaptations.
For example, endurance training expands plasma volume, which can lower measured concentrations of some blood components without necessarily indicating a deficiency.
For endurance and hybrid athletes, this matters because training demands can increase the risk of nutritional shortfalls. A blood test labelled "normal" doesn't automatically mean everything is optimal for your health or training.
But the opposite is important, too: an unusual result doesn't automatically mean something is wrong.
It needs to be interpreted in context.
My thoughts
I like the idea of knowing your own baseline rather than relying on a single blood test and a generic reference range.
If you're training consistently and have a reason to get bloodwork done, keep the results. Ideally, test under similar conditions each time and review changes with your doctor.
And don't jump straight from an unusual result to buying a supplement.
Test when there's a reason. Understand what the result means. Then decide what, if anything, needs to change.
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