Albumin blood value: why endurance athletes often read low

Your albumin blood value is the concentration of the main protein in your blood, usually between 35 and 50 g/l in a healthy adult. It is a concentration, not a quantity. In athletes that distinction carries almost the whole story.

Because a concentration has a denominator. And in endurance athletes that denominator changes.

Regular endurance training expands your plasma volume by 10 to 20 percent (PMID 1874243). You have the same albumin, dissolved in more fluid. The result drops. Nothing is wrong with your liver.

What is albumin and what does it do in your blood?

Albumin is a protein your liver makes, and it accounts for roughly 60 percent of all protein in your blood. It keeps fluid inside your blood vessels, and it transports substances that do not dissolve well on their own: hormones, calcium, bilirubin, fatty acids and many medicines.

That transport role explains why albumin appears on so many results. When your albumin reads low, your measured calcium shifts with it, without anything being wrong with your calcium balance.

Your liver makes about 10 to 15 grams of it per day. A healthy liver holds plenty of spare capacity, so something real has to be happening before production visibly falls.

What is a normal albumin value?

Most Dutch labs use roughly 35 to 50 g/l for adults. The exact range differs by lab and by method, so the range printed on your own result is the one that counts. Above 60 the lower limit usually drops a few points, and during pregnancy the value sits structurally lower.

More important than the number is how much plasma that number had to be diluted into.

The top three rows together explain most mildly abnormal results in athletes. The bottom two are the rows you want a doctor for.

What does a low albumin value mean?

A low albumin value means the concentration sits below the reference range, called hypoalbuminaemia. It is a finding, not a diagnosis. The causes fall into four groups: dilution, loss, reduced production and consumption through inflammation.

In a healthy, hard-training thirty-something, dilution is by far the most likely. Sports medicine has described this pattern for decades as pseudoanaemia: haemoglobin, haematocrit and protein values fall together, while the total amount in your body stays the same or even rises (PMID 10688281, PMID 11495622).

Say you take two men of 34 carrying exactly the same amount of albumin, but one has 3.0 litres of plasma and the other, after two years of endurance training, has 3.5 litres. The first reads 42 g/l, the second 36 g/l.

Same man, same liver, one flagged result.

Want to recognise it? Check whether your haemoglobin and haematocrit fell in the same direction as your albumin. If everything moved down together, that points at your plasma volume. If albumin alone dropped, that is a different story.

Albumin also falls with inflammation, because it is a negative acute phase protein: during inflammation your liver switches production toward other proteins. A low albumin next to a raised CRP is therefore no coincidence.

What if your albumin is too high?

A high albumin value rarely comes from a disease and almost always from haemoconcentration. Too little fluid in your vessels means the same amount of protein in less plasma, so a higher concentration. Standing for a long time before the draw, or a tightly applied tourniquet, pushes the value up too.

Draw after a hot training session without drinking properly and you often see this pattern across the whole result: albumin high, total protein high, haematocrit high. That is one explanation for three values.

There is no condition in which your liver structurally makes too much albumin.

Albumin in blood or albumin in urine: what is the difference?

These are two different tests answering two different questions. Albumin in your blood says something about production, dilution and loss. Albumin in your urine, often measured as an albumin to creatinine ratio, says something about your kidney's filtering function.

In your blood you do not want albumin low. In your urine you do not want it high, because healthy kidneys barely let this protein through.

To work out which one you have, look at the unit and the material. Serum or plasma in g/l is the blood test. Urine in mg/mmol or mg/l is the kidney test.

Does your training change your albumin value?

Yes, and in two ways at once. Long term, endurance training lowers your value through a larger plasma volume, and it stays lowered as long as you stay in shape. Short term, a hard session can push the value up briefly through fluid loss, then drop it below your baseline.

That second movement lasts roughly a day or two. Draw on a Monday morning after a hard Sunday and you land right in that dip.

If you want a value that says something about you rather than about your weekend: draw after 24 hours without hard training, well hydrated, and not straight after travel or a sauna. The same rule applies to your whole blood count, as covered in fasted blood draws for athletes.

When should you discuss an abnormal albumin value with your GP?

When the value stays low on a calm repeat, especially alongside fluid retention in your ankles, foamy urine, unintended weight loss or abnormal liver or kidney values. A single mildly low result without symptoms is usually not that on its own.

Thuisarts describes an abnormal blood result as a reason to look further, not as a diagnosis, and the NHG guidelines approach albumin the same way. RIVM points out that reference values differ per laboratory in blood testing, which matters directly for this protein when deciding whether your result is flagged.

Take your full result with you. With albumin, the rest of the panel is literally the context that makes the number mean anything.

Where do you start?

First check whether your haemoglobin and haematocrit fell along with your albumin. If they did, you probably have your explanation before you start searching. Then repeat in a calm week, well hydrated, and compare the two results side by side.

Our complete blood count test reports your red series with an assessment by a BIG-registered doctor, so you do not have to make that comparison alone.

How all the values connect is covered in complete blood count explained and in the complete biomarker guide for athletes. For the protein albumin forms part of, read total protein in your blood. And if your haemoglobin fell with it, blood values for endurance athletes is the next step.

References

1. Athletes' pseudoanaemia. European Journal of Applied Physiology and Occupational Physiology. 1991. PMID 1874243.
2. Fallon KE, Fallon SK, Boston T. Sports haematology. Sports Medicine. 2000. PMID 10688281.
3. Runner's anemia. JAMA. 2001. PMID 11495622.
4. RIVM. Blood testing and reference values. Accessed 2026.
5. NHG. Dutch College of General Practitioners, laboratory diagnostics in primary care. Accessed 2026.
6. Thuisarts. My blood result is abnormal. Accessed 2026.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. For treatment decisions, discuss your results with your GP.