wie lange vor blutabnahme nichts trinken — when to see a doctor?

Fasting requirements before a blood draw depend on the specific test. For glucose and lipid panels (cholesterol, triglycerides), 8–12 hours without food but with water allowed is standard. Other tests like liver enzymes or thyroid hormones often do not require fasting. Drinking water is generally permitted as long as it is unsweetened and non-caffeinated. The question 'when to see a doctor' is context-dependent: seek medical advice if lab results are abnormal, symptoms persist, or a high genetic risk (e.g., polygenic risk score for heart disease) is identified. Direct-to-consumer tests like MyBody-X provide indications, not diagnoses. Evidence for fasting guidelines is based on clinical practice, not robust trials, so the evidence level is 'practice'. Caution: prolonged fasting can alter metabolism; always follow specific instructions from your lab or physician.