Blood Test and Lab Appointments: Fasting and Other Preparation

Start with your lab order

Your provider decides which tests you need and how to prepare. Read the instructions on your lab order or patient portal, and ask the office if anything is unclear. Many tests need no preparation at all beyond answering a few questions, according to MedlinePlus; others need specific steps.

Booking at a lab

Labs inside a clinic or hospital, and commercial lab chains, often take appointments online or by phone and may also accept walk-ins. Booking a time can shorten your wait, especially early in the morning when many people come in fasting. Check:

• that the lab accepts your insurance, and is the lab your provider or plan wants you to use;
• whether you need to bring a paper order or whether it was sent electronically;
• the lab’s hours for the specific test (some collections have time limits).

Fasting

MedlinePlus explains that fasting means not eating or drinking anything except water for up to several hours or overnight before the test, because nutrients from food in your bloodstream can change some results. Your instructions will say how long. Book an early-morning appointment if you need to fast — it makes the wait easier.

Other preparations MedlinePlus mentions for certain tests include avoiding specific foods or drinks (such as alcohol), avoiding strenuous exercise, and drinking extra water before some blood tests so veins are easier to find.

Medicines and supplements

Tell your provider about all medicines, vitamins and supplements you take. MedlinePlus advises not to stop any medicine unless your provider tells you to. Some medicines can affect certain results, which is why your provider may give specific timing instructions.

Be honest if something went wrong

If you ate, took a medicine or missed a step, tell the lab staff. MedlinePlus notes that even a minor change from the instructions can affect results, and it is better to reschedule than to get a misleading result.

What to bring

• Photo ID and insurance card.
• Your lab order, if you were given a paper one.
• A list of medicines.
• A snack and drink for after a fasting test.

Wear a top with sleeves that roll up easily. If you tend to feel faint during blood draws, tell the staff — they can have you lie down.

Getting results

Ask how and when results will be shared — often through your provider’s patient portal — and who will explain them to you.