Blood values for athletes - what to test

5 min read

You train consistently, eat well, sleep enough, and yet you stagnate. Or you feel inexplicably tired, your performance drops, or your recovery is slower than normal. Sometimes the answer lies in your blood.

Why blood values matter

Deficiencies in specific vitamins, minerals, or hormones can significantly slow down your performance and recovery without you having clear symptoms. An iron deficiency reduces your oxygen transport. Vitamin D deficiency inhibits your muscle growth and immune function. A suboptimal thyroid level makes everything slower.

Many of these deficiencies are easy to detect with a blood test and easy to correct. But you need to know what to have tested.

The essential tests for athletes

• Complete blood count (Hb, Ht, MCV, MCH) - Screens for anemia. Low hemoglobin reduces your oxygen transport and thus your endurance and recovery.
• Ferritin - Iron storage. Can be low before your hemoglobin drops. Optimal for athletes: 50-150 ng/mL (the lower limit of the laboratory is often too low for athletes).
• Vitamin D (25-OH) - In the Netherlands, 40-60% have a deficiency, especially in winter. Optimal: 75-125 nmol/L. With deficiency: supplement 2000-4000 IU per day.
• Vitamin B12 - Important for energy and nerve function. Especially at risk for vegetarians and vegans.
• Thyroid function (TSH, free T4) - A slow thyroid slows down your metabolism, your recovery, and your energy level.
• Testosterone (total + free) - Relevant with persistent fatigue, performance stagnation, loss of libido. Have it drawn fasting in the morning for the most reliable value.
• CRP (inflammation marker) - An elevated CRP can indicate chronic overload, infection, or inflammation.
• Kidney function (creatinine, eGFR) - Relevant if you eat a lot of protein. With healthy kidneys, high protein intake is safe, but monitoring is wise.
• Liver function (ALAT, ASAT) - Can be elevated due to supplement use or heavy training (ASAT rises after strength training).

How often to test

If you have no complaints, an annual check is sufficient. With specific complaints or after starting supplementation, have a retest done after 3 months to see if the values have normalized.

Practical tips

• Have blood drawn fasting, in the morning before 10:00 AM for the most reliable values
• Don't have blood drawn the day after heavy training (ASAT and CK are then elevated due to muscle damage)
• Always ask for the exact numbers, not just whether it's normal - laboratory reference ranges are broad and not always optimal for athletes
• Discuss abnormal values with your doctor before you start supplementing yourself

An annual blood test is one of the smartest investments you can make as an athlete. It costs little and can detect problems before they set you back months.