How to prepare for a blood test

A blood test is a snapshot of one moment. What you ate, how you slept and what you did the day before all show up in that snapshot. Good preparation means the result reflects your usual health, not a bad night or a big dinner.

Fast if your panel asks for it

Glucose, insulin and triglycerides rise after a meal. If your panel includes them, fast for 8 to 12 hours before your draw. Water is fine and actually helps, because a well hydrated arm makes the draw quicker. Skip coffee, tea with milk, juice and chewing gum until afterwards.

Go in the morning

Several hormones follow a daily rhythm. Testosterone and cortisol are highest in the early morning and fall through the day. A morning draw, ideally before 10am, gives a result that can be compared with the reference range and with your own past results.

Pause biotin, keep your usual medication

High dose biotin, often found in hair, skin and nail supplements, can interfere with the lab methods used for thyroid hormones, vitamin levels and some heart markers. Stop it at least 48 hours before your test. Keep taking prescribed medication as normal unless your doctor has told you otherwise, and tell us what you take so it can be considered in your report.

Rest before the draw

A hard gym session or a long run in the 24 to 48 hours before your test can raise muscle enzymes such as CK and AST, and can nudge kidney markers. Alcohol the night before can affect liver enzymes and triglycerides. A quiet day before your test keeps these from muddying the picture.

If you are unwell, wait

A cold, flu or any infection can temporarily raise inflammation markers and change iron, white cell and even hormone results. Unless your doctor wants a test during the illness, it is usually better to wait two weeks after you feel well again.