was trinken vor blutabnahme — which blood markers matter?

The question about what to drink before a blood draw is not directly addressed in the provided contexts. Standard medical practice advises: plain water in moderate amounts is generally allowed and can improve vein access. However, coffee, tea, juices, or sugary drinks should be avoided because they can affect blood glucose, insulin, triglycerides, and some liver enzymes. Alcohol also distorts many markers (e.g., GGT, HDL, glucose). For most routine blood tests (CBC, renal panel, electrolytes), water is safe. For fasting blood draws (glucose, lipid profile), no calories should be consumed. The DNA-based information in the contexts (e.g., TCF7L2, MTNR1B) is not relevant for immediate pre-test preparation. Caution: Always follow your doctor's specific instructions. Evidence: practice (general medical knowledge, not from provided context).