welche blutwerte sind wichtig bei müdigkeit — which blood markers matter?

Fatigue can have many causes, and blood markers help narrow them down. Key markers include: - **Ferritin** (iron stores): Low ferritin (<30 ng/ml) indicates depleted iron, a common cause of fatigue even without anemia. Supplementation should be medically supervised (source: deep-qa-batch-2283). - **TSH and free T4** (thyroid): Hypothyroidism (elevated TSH) often presents with fatigue. Borderline TSH requires full workup, not self-supplementation with iodine (source: deep-qa-batch-2283). - **Vitamin B12 and folate**: Deficiency causes fatigue, neurological issues, and macrocytic anemia. Check especially in vegans, elderly, or post-gastrectomy. - **Vitamin D**: Deficiency is linked to fatigue and muscle weakness, though evidence for causality is moderate. - **Complete blood count (hemoglobin, MCV)**: To rule out anemia. - **CRP / ESR**: Chronic inflammation can cause fatigue. - **Fasting glucose, kidney and liver function**: To exclude diabetes, renal failure, or liver disease. - **Testosterone (in men)**: Free testosterone is more informative than total, as SHBG regulates bioavailability (source: deep-nvidia-bio-testosterone). **Limitations**: Direct-to-consumer (DTC) tests often provide isolated values without clinical context. A normal result does not rule out a treatable cause. Evidence for GPX1 variants or selenium in fatigue is mechanistic only, not clinically established (source: deep-qa-batch-1033). **Safety note**: Persistent fatigue warrants a medical workup. Self-supplementation (e.g., iron, iodine, selenium) can be harmful in excess.