Blood values explained: the complete biomarker guide for athletes

This guide explains per system what your most important blood values mean, from your heart and blood count to your kidneys, liver, hormones and vitamins. Treat it as a reference: you look up the marker on your result and read what it says. If you want to know which test fits your training goal, we point you to the right in-depth guide.

I think a result only gains value once you understand what you read. A row of numbers without context leads to needless worry or falsely reassured feelings. With this guide you place each value next to the explanation that belongs with it, so you know what you really measure.

Which blood values matter for athletes?

For athletes it comes down to a few systems: your heart and blood fats, your blood count, your kidneys and liver, your hormones and your vitamins. Per system there are a few markers that say the most. The table below links each system to its core markers and the in-depth guide.

Below we walk through these systems one by one.

Heart and blood fats: ApoB, cholesterol and omega-3

You do not read your heart risk from a single cholesterol number, but from the count of harmful particles in your blood. ApoB counts those particles and predicts risk more accurately than LDL cholesterol alone (Sniderman, 2019). On top of that, your omega-3 index says something about your fatty acid status and your recovery.

For an athlete this matters because good fitness does not automatically remove your heart risk. You can be fit and still have unfavourable blood fats.

Dig into ApoB and the omega-3 index. For your full heart picture, read our guide cholesterol and your heart values.

Blood count: hematocrit, hemoglobin and iron

Your blood count determines how much oxygen your blood can carry, and that touches your endurance directly. Hematocrit is the percentage of red blood cells, hemoglobin the oxygen-carrying protein and ferritin your iron store. Together they tell you whether your oxygen transport is in order.

In athletes two extremes play out. A too-high hematocrit makes your blood thicker, while a low ferritin undermines your performance.

Read on in high hematocrit. For your iron store and endurance performance, the guide blood values for endurance athletes is a logical next step.

Kidneys and muscle breakdown: creatinine and protein

Creatinine is a waste product of your muscles, and muscular athletes naturally have more of it. A raised creatinine in a lifter therefore does not automatically mean a kidney problem. That is why a doctor also looks at the eGFR, an estimate of your kidney function.

Your protein intake also raises questions. Many athletes wonder whether a lot of protein strains their kidneys.

Read high creatinine from muscle mass and protein intake and your kidneys. If you use creatine as a supplement, that changes your creatinine, which we explain in creatine and your blood values.

Liver and lifestyle: what alcohol does

Your liver values, such as ALT, AST and gamma-GT, give a picture of how your liver is doing. They can rise temporarily after a hard session or after alcohol, which makes reading the result harder. A one-off rise therefore says less than a trend.

Alcohol touches not only your liver, but also your recovery and your sleep. For an athlete that counts double.

Read what alcohol does to your values in alcohol and your blood values.

Hormones and metabolism: testosterone, thyroid and insulin

Your hormones steer your recovery, your muscle growth and your energy. Testosterone is the best-known marker for many athletes, but your thyroid and your insulin sensitivity count just as much. Together they set the pace and quality of your recovery.

A thyroid that works too slowly or too fast, you often feel first in your training. Insulin resistance undermines your metabolic health in the background.

Dig into the guide testosterone: symptoms and blood values, into thyroid and metabolism, and into measuring metabolic health.

Vitamins and minerals

Vitamins and minerals steer your energy, your recovery and your hormone balance, often without you noticing a deficiency. The most important for athletes are vitamin D, vitamin B12, iron, magnesium and zinc. A deficiency regularly explains complaints you would otherwise blame on your training.

Because a standard draw often skips these values, they stay a blind spot. Measuring makes that blind spot visible.

You find the full explanation in our guide vitamins and minerals for athletes.

Stress and recovery: cortisol and CK

Some values say something about how your body handles stress and load. Cortisol is your main stress hormone, and it has a clear daily rhythm: high in the morning, lower in the evening. CK, or creatine kinase, rises after muscle damage and is a rough measure of how hard a session landed.

For an athlete these are sensitive markers. A high CK right after a hard session is normal, but a persistently high value can point to insufficient recovery.

So measure cortisol at a fixed moment, ideally in the morning. A one-off value says less than a pattern over the day.

If you want to spot overload early, read these values next to your training load and your sleep. A deviation you discuss with your doctor.

Inflammation and recovery: CRP and ESR

Inflammation values tell you something about how your body responds to load and recovery. CRP and ESR are the best known, and they rise with an infection or after heavy effort. For an athlete the context matters most: a temporary rise after a marathon is different from a chronically raised value.

A slightly raised CRP without a clear cause can point to low-grade inflammation, something that can slow your recovery in the background. That is why a repeat measurement at rest is valuable.

So do not plan your measurement right after a hard session. A high CRP from muscle damage is not a disease, but it can cloud your picture if you do not know it.

So always read inflammation values together with your training load. A deviation you discuss with your doctor, who weighs your whole situation.

Blood sugar: glucose, HbA1c and insulin

Your blood sugar balance says a lot about your metabolic health, even if you are lean and trained. Fasting glucose is a snapshot, HbA1c gives your average blood sugar over weeks and fasting insulin shows early whether your sensitivity is dropping. Together they sketch a fuller picture than glucose alone.

Insulin resistance can arise years before a deviating glucose. That is why many optimizers track their insulin and HbA1c in particular.

For an athlete this matters because your training status does not automatically make your sugar balance perfect. Nutrition and sleep play a big role.

You read the full explanation in our guide measuring metabolic health.

Proteins and hydration: albumin and total protein

Protein values such as albumin and total protein give a picture of your nutritional status and your fluid balance. A deviation can say something about your liver, your kidneys or simply your hydration at the moment of the draw. That is why you always read them together with your other values.

For an athlete, hydration plays an underrated role. Drawing blood dehydrated can temporarily skew your values a little.

So make sure you have drunk enough before you have your blood taken. That way you prevent a skewed picture from worrying you needlessly.

Here too: the combination of values tells you more than a single number.

How do you read your blood values?

You always read a blood value next to the labs reference range and next to your own complaints. A value just outside the range is not immediately a problem, and a value within the range does not rule out everything. The context decides the meaning.

According to Thuisarts a blood test is often used in a targeted way for specific complaints, not as a loose check of everything at once. The RIVM also publishes population figures that help to put your own value in perspective.

The most important rule is: follow the trend. A repeat measurement at a comparable moment says more than a single snapshot.

Which test fits you?

Which test you choose depends on your goal and your sport. If you want to understand your biomarkers, this guide is your starting point. If you want to know which values fit your training type, our sport-specific guides take you further.

For strength athletes we cover what training and supplements do to your values in blood values for strength athletes. For endurance athletes it comes down to iron and recovery in blood values for endurance athletes.

Compose your own panel through our custom blood test, or start with the broad 360 Health blood test that combines most of these systems. An extensive explanation of that panel you read in the complete guide to the 360 health panel.

Common mistakes when reading your blood values

The biggest mistakes sit not in the measurement, but in the interpretation. Anyone who tracks their values seriously often runs into the same traps.

The first mistake is overrating a single result. Your values move with your training, your fluid balance and the season, so a snapshot can mislead.

The second mistake is reading markers in isolation instead of as a whole. A raised creatinine in a muscular lifter means something different than the same value in someone without much muscle mass. The combination tells the story.

The third mistake is being alarmed by a value just outside the range and adjusting yourself at once. A deviation you discuss with your doctor, who weighs your whole picture.

Frequently asked questions

The questions I get back most from athletes who want to really understand their blood values for the first time.

Which blood values should I test as an athlete? A useful base covers your blood count, your kidney and liver values, your blood fats, your hormones and your most important vitamins. Which exactly you choose depends on your goal and your complaints.

How often should I test my blood? For most athletes without complaints, once or twice a year is enough. If you spot something and adjust, a retest after a few months is useful.

What if a value is just outside the range? That is often no reason to panic. A repeat measurement and a talk with your doctor help to decide whether something is really going on.

Do I need to fast? For some values such as glucose and triglycerides yes, for others no. Preferably draw blood at a fixed moment, so your measurements stay comparable.

References

1. Sniderman AD, Thanassoulis G, Glavinovic T, et al. Apolipoprotein B Particles and Cardiovascular Disease: A Narrative Review. JAMA Cardiology. 2019. PMID: 31642874.
2. Thuisarts.nl / NHG. Blood testing. Accessed 2026.
3. RIVM. Population figures and reference values. 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. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. For treatment decisions, discuss your results with your GP.