In one sentence
A Nüchternblutabnahme is a blood draw done on an empty stomach, usually after 8 to 12 hours without food. Water is fine. It matters for values like blood sugar and blood fats, not for the blood count itself.
Nüchtern means you come to the blood draw on an empty stomach. In practice that means no food for around 8 to 12 hours before the appointment. Water without anything in it is fine and even helpful, because it makes the blood draw easier. Coffee with milk or sugar, juice and breakfast all count as food.
Fasting matters because some values change after eating. Blood sugar rises after every meal, and blood fats like triglycerides can stay raised for hours. If those values are measured shortly after breakfast, the result describes your breakfast more than your body. Values like the großes Blutbild are barely affected by food, so a blood count alone does not need fasting.
Whether you need to come nüchtern depends on which values your doctor ordered, so the honest answer is always: ask the practice when you book. Morning appointments make fasting easiest, since most of the fasting hours happen while you sleep.
If you take regular medicines, do not simply skip them. Ask the practice beforehand whether to take them as usual or after the blood draw.
This glossary entry is general information, not medical advice, and it is not intended to diagnose, treat or rule out any condition. Discuss your own results with a clinician who knows your history.
