Blood Tests for Athletes: The Values You Should Know

You measure your weights, your sleep duration and perhaps your resting heart rate. But some of the most important health values remain invisible until you have them measured in a lab. Iron deficiency can disguise itself as "poor form" for months, rising long-term blood sugar goes unnoticed, and high blood lipids don't hurt.

This article explains which blood values are meaningful for athletes, how training can skew them and how to prepare properly. It belongs to the Men's Health topic but applies to everyone who trains.

The key values at a glance

Iron and ferritin: the hidden performance killer

Iron is central to oxygen transport. Empty iron stores often show up long before actual anaemia as fatigue, poorer recovery and declining endurance performance. Particularly affected are:

• endurance athletes with high volumes
• people who menstruate
• vegetarians and vegans
• blood donors

Important: ferritin rises with inflammation and infections and can then mask a deficiency. Never take iron "just in case" – too much is harmful too. Measure first, then decide with your doctor.

Vitamin D: almost always an issue in winter

In Central Europe, the sun between October and March is hardly enough for the body to produce sufficient vitamin D. Many people therefore have low levels in winter. The test measures 25-OH vitamin D. Values below about 20 ng/ml (50 nmol/l) are often considered insufficient and below about 12 ng/ml (30 nmol/l) a clear deficiency – the exact thresholds differ between professional bodies. More in Vitamin D deficiency.

Blood sugar and lipids: prevention for heart and vessels

Exercise significantly lowers the risk of type 2 diabetes and cardiovascular disease – but doesn't protect completely. Genes, diet and body fat play a role. HbA1c shows average blood sugar over recent months and is well suited to early detection. LDL cholesterol is the most important lipid value for cardiovascular risk. How training and nutrition improve the values is explained in Heart health and training and Lowering cholesterol.

How training skews lab results

Active people in particular often get surprises in their lab report. The most common distortions:

If you take creatine, always say so – more in Creatine: effects and myths.

Preparing properly for a blood test

1. 1

   Step 1

   Plan your training

   Avoid hard or unfamiliar training for 48 to 72 hours before the blood test, especially heavy strength training or long endurance sessions.

2. 2

   Step 2

   Arrive fasted

   Don't eat for eight to twelve hours beforehand. Water and unsweetened tea are fine.

3. 3

   Step 3

   Get measured in the morning

   Many values such as testosterone and cortisol fluctuate over the day. An appointment between 7 and 10 am makes measurements comparable.

4. 4

   Step 4

   Bring information

   Note your supplements (for example creatine, vitamin D, iron), medications and training load and share them with your doctor.

5. 5

   Step 5

   Compare results

   Ask for your values and compare them with earlier measurements – trends are often more meaningful than a single value.

Testosterone and hormones

For men with typical symptoms such as loss of libido, persistent fatigue or muscle loss despite training, testosterone can be worth measuring – always in the morning and fasted, and repeated if abnormal. What affects the level and how to support it naturally is explained in How to increase testosterone naturally. Without symptoms, routine hormone testing is usually not necessary.

Blood values and everyday data

Lab values are snapshots. Wearables, in contrast, provide continuous data such as resting heart rate, heart rate variability and sleep. The two complement each other: a resting heart rate rising over weeks and falling HRV can, for example, be a reason to have iron levels or the thyroid checked. How to read this everyday data is explained in Understanding HRV.

Three typical findings in athletes

"My liver values are elevated." Often after a hard strength session in the days before. AST and ALT then come from the muscles. A follow-up after a few days' rest – supplemented by the more liver-specific value GGT – brings clarity.

"My creatinine is too high." Often harmless with high muscle mass and creatine use. Your doctor can assess kidney function more precisely with a second marker such as cystatin C.

"I'm always tired, but my blood count is normal." Normal haemoglobin doesn't rule out empty iron stores. Only ferritin shows how full the stores are – and it should always be interpreted together with an inflammatory marker.

What a blood test can't do

• It doesn't replace a physical examination or a conversation with your doctor.
• A single value outside the range is not automatically pathological – context and repetition decide.
• "Optimal" values from the internet are often stricter than medical reference ranges and lead to unnecessary worry or supplementation.

How often to measure?

• Healthy recreational athletes: a basic check once a year.
• High-volume endurance athletes, vegetarians, vegans: ferritin and B12 more often if needed.
• During longer diets or intense training blocks: interim checks after consulting your doctor.
• From about age 35–40: keep an eye on blood sugar and lipids regularly; many health systems offer a routine check-up from this age.

Conclusion: measure, understand, act deliberately

An annual look at your lab values is as much part of an athlete's planning as the training log. Properly prepared and medically interpreted, blood values often reveal problems long before they slow your performance – and stop you taking supplements you don't need. How to lower blood pressure with training is covered in Lowering blood pressure through exercise.