<\/p>\n
There is a very common temptation among those who train: to turn a blood test into a kind of \u201cperformance exam.\u201d The more parameters, the better. And if any one of them appears slightly outside the laboratory\u2019s reference range, we immediately think that something is wrong. The reality is quite different.<\/p>\n
A blood test does not directly measure how far you will run, how much weight you will lift, or whether you are recovering well from your last session.<\/strong> It is used to detect health problems, nutritional deficits, and certain abnormalities that can affect performance. And, above all, it allows monitoring an athlete\u2019s progression over time.<\/p>\n In fact, current reviews on biomarkers in sport emphasize a fundamental idea: results should be interpreted taking into account the athlete\u2019s usual level, recent training, diet, hydration, sleep, sex, recent illnesses, and context. An isolated value can tell much less than it appears.<\/p>\n If we had to choose one essential block, it would be the complete blood count<\/strong>.<\/p>\n Here we find several parameters, but for the athlete there are four that are especially interesting:<\/p>\n The hemoglobin<\/strong> is particularly important because it is responsible for transferring oxygen from the lungs to the tissues. If there is anemia, the capacity to transport oxygen can decrease, and aerobic performance can be affected.<\/p>\n As a general reference, the WHO considers anemia in adults as a hemoglobin below 13 g\/dL in men and 12 g\/dL in non-pregnant women. But in athletes, care must be taken not to interpret the number in isolation: training can increase plasma volume and cause a \u201chemodilution\u201d that modifies some blood values without necessarily indicating disease.<\/p>\n Therefore, more than chasing a \u201cperfect\u201d hemoglobin, it is important to know your usual value and observe its evolution.<\/p>\n If you practice endurance sports, you are a female athlete, have heavy menstruation, follow a vegetarian or vegan diet, or have experienced an unexplained drop in performance, there is one value that deserves particular attention: ferritin.<\/p>\n Ferritin serves as an indicator of the body\u2019s iron stores.<\/p>\n And here lies one of the big confusions: you can have normal hemoglobin and, nonetheless, have low iron reserves<\/strong>.<\/p>\n In sports medicine it is usually considered that ferritin below 15 \u00b5g\/L indicates nearly depleted stores, and that between 15 and 30 \u00b5g\/L there are low reserves. Therefore, 30 \u00b5g\/L is frequently used as a practical threshold in athletes.<\/p>\n But you should not obsessively chase an extremely high ferritin either. In an athlete without a deficiency, artificially increasing iron does not automatically provide more oxygen or better performance.<\/p>\n If ferritin is low, you also need to investigate why<\/strong>: insufficient diet, menstruation, blood losses, absorption problems, or high training demands may be behind it.<\/p>\n When there is a suspicion of iron deficiency, ferritin alone is not always enough.<\/p>\n The transferrin<\/strong> is the protein responsible for transporting iron in the blood, and the transferrin saturation<\/strong> helps us know how much of that transport capacity is occupied by iron.<\/p>\n Serum iron by itself is quite less useful: it can vary during the day and be influenced by different factors.<\/p>\n Therefore, when there is a suspicion of deficiency, it makes more sense to evaluate together:<\/p>\n Hemoglobin + MCV + ferritin + transferrin\/saturation of transferrin.<\/strong><\/p>\n This combination allows a better distinction between a simple isolated variation and a genuine problem with iron metabolism.<\/p>\n Vitamin B12 and folate participate in red blood cell formation and in the proper functioning of the nervous system. They are especially relevant if you follow a vegan or vegetarian diet, have digestive or absorption problems, or there is an alteration in the blood count.<\/p>\n Vitamin B12<\/strong> deserves particular attention because a deficiency can cause anemia and neurological symptoms. In athletes with a properly balanced diet there is no reason to try to raise B12 indefinitely through supplements.<\/p>\n In other words: the goal is to correct a deficiency, not to achieve a spectacular lab value<\/strong>.<\/p>\n Vitamin D has become one of the star values in sports analytics. And it makes sense to monitor it, especially in athletes with little sun exposure, training mainly indoors, restrictive diets, or a history of bone problems.<\/p>\n Vitamin D<\/strong> participates in bone and muscle health, so a deficiency can be relevant for a sportsperson. However, having higher vitamin D than another athlete does not automatically mean you will perform better. Therefore, we should not turn it into a performance marker, but rather fundamentally into a health indicator and a sign of nutritional sufficiency<\/strong>. Reviews on sports laboratory testing include vitamin D, calcium, and markers of bone metabolism, especially when there is a risk of stress injuries.<\/p>\n A athlete remains a person who needs to monitor cardiovascular and metabolic health. Fasting glucose, total cholesterol, HDL, LDL, and triglycerides can be part of a general blood test, especially if there is a family history, overweight, hypertension, or other risk factors.<\/p>\n It is also useful to check kidney function through parameters such as creatinine and urea<\/strong>, although the athlete has a peculiarity: a muscular person or someone who has trained recently may present elevated creatinine without any kidney disease.<\/p>\n The same goes for urea, which can rise with high protein intake, dehydration, or a heavy training load. Therefore, a result slightly outside the range should not automatically be interpreted as pathological.<\/p>\n AST, ALT, GGT, and other liver markers commonly appear in a blood test. But the athlete has a notable peculiarity: some enzymes we associate with the liver are also present in muscle. After intense training, especially strength work, AST can rise, and so can CK (creatine kinase) as a consequence of muscle stress.<\/p>\n This explains why a blood test taken immediately after a hard session can look quite different from another taken after several days of recovery. In a study of elite athletes, the most frequent abnormalities during routine screening were increases in AST, phosphate, CK, urea, and bilirubin, and many of them had no clinical relevance.<\/p>\n The takeaway is clear: do not interpret a sports blood test as if you were a sedentary person who hasn\u2019t trained for days.<\/strong><\/p>\n Creatine kinase (CK)<\/strong> rises when there is muscle damage or stress. It can be interesting for interpreting the response to a training load, especially if there are prior individual values. But it is not a universal \u201cgreen light.\u201d<\/p>\n A high CK does not necessarily mean you are overtrained, nor does a normal CK guarantee you are perfectly recovered. The differences between individuals are enormous, and recent exercise has a huge influence on the result. If you had a blood test 24\u201348 hours after running a marathon and doctors did not know you had participated, they would likely admit you to the hospital. CK levels can spike massively after a marathon, typically reaching 10,000 to 20,000 U\/L (units per liter), whereas a normal reference value is usually between 25 and 200 U\/L.<\/p>\n Current recommendations on biomarkers of training load precisely warn of this difficulty: the values must be interpreted relative to the individual level and the context, not by using population reference ranges alone.<\/p>\n CRP<\/strong> can be used as a marker of inflammation. It can be informative when there are symptoms, infections, injuries, or a specific clinical suspicion. But it is not a direct marker of \u201crecovery.\u201d A small elevation can have multiple explanations, including a response to exercise.<\/p>\n Therefore, there is little point in obtaining a CRP after every week of training to decide whether to rest.<\/p>\n This is where many sports analyses begin to turn into a collection of numbers that are difficult to interpret. Testosterone, cortisol, TSH, T3, T4, and other hormones can be very useful when there is a concrete clinical question<\/strong>. But they should not be used as a daily marker of \u201canabolism,\u201d \u201cstress,\u201d or \u201cfatigue.\u201d<\/p>\n Cortisol, for instance, varies with the time of day, stress, sleep, and exercise. Testosterone also shows substantial fluctuations. Moreover, in athletes with low energy availability there can be disruption of various hormonal axes. In this context, the blood test can be part of a broader RED-S assessment (relative energy deficiency in sport), but it should never be interpreted in isolation. The International Olympic Committee\u2019s consensus on RED-S recommends integrating clinical, physiological, and performance indicators.<\/p>\n For a healthy person who trains regularly, a reasonable starting point would be:<\/p>\n Basic<\/p>\n Complete blood count<\/strong><\/p>\n Iron<\/strong><\/p>\n Biochemistry<\/strong><\/p>\n Metabolism<\/strong><\/p>\n According to the athlete<\/p>\n Add vitamin D, vitamin B12, folate, TSH, CRP, CK<\/strong> or other parameters when there are risk factors, symptoms, a specific diet, a high training load, or a medical indication.<\/p>\n There is no universal frequency. A healthy athlete can schedule periodic checks within their medical reviews, while someone with iron deficiency, symptoms, significant dietary changes, or a very high training load may need more frequent monitoring.<\/p>\n And there is something even more important than frequency: repeat the analysis under comparable conditions<\/strong>. If we want to understand an athlete\u2019s evolution, it is far more useful to compare results obtained in similar circumstances than to obsess over the laboratory\u2019s reference range.<\/p>\n<\/div>\n1. Hematology: the starting point<\/h5>\n
2. Ferritin: probably the most important nutritional parameter<\/h5>\n
3. Transferrin and transferrin saturation: completing the iron picture<\/h5>\n
4. Vitamin B12 and folate: important, but not for everyone<\/h5>\n
5. Vitamin D: more linked to health than to \u201cmore performance\u201d<\/h5>\n
6. Glucose, lipid profile, and kidney function: health also matters<\/h5>\n
7. Transaminases: beware of alarm at an elevated AST<\/h5>\n
8. CK: can it tell you if you are recovered?<\/h5>\n
9. C-reactive protein: is there inflammation?<\/strong><\/h5>\n
10. And testosterone, cortisol, and other hormones?<\/h5>\n
So, what should an athlete ask for?<\/strong><\/h4>\n
How often should you get a blood test?<\/h4>\n