Hemoglobin A1C Testing Blood Test: How to Prepare, Fast

At a glance

Hemoglobin A1C Testing Blood Test: prep snapshot

Sample type: Blood draw
Fasting: Fasting is often not required for a hemoglobin A1c test, but some locations or combined test…
Best collection time: An A1c sample can generally be collected at any time of day.
Typical turnaround: Varies by collection lab
Category: Metabolic & Glucose

Below is a plain-language prep guide for the hemoglobin a1c testing, including sample type and timing basics. Hemoglobin A1c testing uses a blood sample to show how well blood sugar has been controlled over time.

What this test looks at

This test measures hemoglobin A1c, the glycated form of hemoglobin, as a percentage of total hemoglobin. That percentage reflects how blood glucose has averaged out over the preceding weeks and months. Clinicians use it alongside other glucose results to assess overall control.

Hemoglobin A1c
Glycated hemoglobin
Average glucose control

Preparation checklist for the Hemoglobin A1C Testing

Standard preparation covers most A1c tests, so no special routine is usually required. Confirm any timing or fasting instructions with the testing location before your visit.

Check with the collection lab about whether fasting is needed for your appointment.
Unless told otherwise, eat and drink normally and take routine medications as usual.
Stay hydrated by drinking water before your draw, which can make the blood draw easier.
Bring a list of current medications and supplements, plus any prior glucose or A1c results.
Wear a short-sleeved or loose-sleeved shirt so the arm is easy to access.
Tell the collector if you have had recent illness, transfusion, or a change in diabetes treatment.

Fasting, timing, sample type, and what to bring

Fasting

Fasting is often not required for a hemoglobin A1c test, but some locations or combined test panels may ask for it, so confirm with your lab.

Best time to collect

An A1c sample can generally be collected at any time of day. Many clinicians repeat the test on a regular schedule to track trends, so follow the timing your care team recommends.

Sample type

Blood draw. The collector will explain the process before starting.

What to bring

Your order confirmation email, in case the collection site asks to see it
Your printed lab order or requisition form — the ordering physician prepares it for you after you order, and you print it (or fax it from your account) before visiting
A short-sleeved or loose-sleeved shirt for an easy blood draw
Water to drink before the draw and a light snack for afterward, if your test requires fasting
A government-issued photo ID (most collection sites verify identity at check-in)
A written list of the medications and supplements you currently take

You do not need an insurance card or a payment method at the collection site: the lab does not bill insurance, and you pay at order time, so there is no copay or deductible. The lab also provides the physician's requisition, so you do not need a separate doctor's referral.

Order process and what-to-bring details reflect the lab's published instructions, paraphrased in our own words. Confirm final requirements with the collection lab that will perform your draw.

The collection visit, step by step

A collector cleans an area on your arm, applies a tourniquet, and draws a small tube of blood from a vein, usually in the inner elbow. The sample is labeled and sent to a lab, and the draw itself typically takes only a few minutes.

Details worth confirming with the collection lab before your visit:

Does this test require fasting or any change to my medications?
Is there a preferred time of day or window for collecting my sample?
When should I expect results, and who will review them with me?

Why a clinician may order this test

A clinician orders hemoglobin A1c testing to monitor how well diabetes is being controlled over time. It may also be used to screen for elevated average glucose in people with risk factors, depending on the clinician's judgment.

Reading your results responsibly

Results are usually reported as a percentage, and the reference range or target varies by lab and by the person being tested. Your clinician interprets the number along with your history, so compare results only against the range provided with your report.

General test information is compiled from publicly available reference material, including MedlinePlus (medlineplus.gov) and the Centers for Disease Control and Prevention (cdc.gov), and is reviewed for clarity. Preparation and what-to-bring details reflect the lab's published instructions, paraphrased into our own words. Preparation instructions, timing, and pricing vary by collection lab — always confirm them with the lab that will perform your draw.

Common questions

Frequently asked questions

Do I need to fast for a hemoglobin A1c test?

In many cases fasting is not required, because the test reflects a longer-term average rather than a single moment. Some locations or combined test orders may still ask for fasting, so confirm with your lab.

How long does the A1c result reflect?

Because it is based on red blood cells, the result reflects average glucose over roughly the preceding couple of months to a few months. That is why it is used for tracking control rather than a single day's readings.

How soon will I get my results?

Turnaround is commonly about one to three business days, though it can vary by lab and by how the sample is shipped. Ask your collection site for its typical timeline.

Can anything change my A1c result?

Some conditions that affect red blood cells, such as recent transfusion or certain blood disorders, can influence the result. Tell your clinician and the collector about recent illness, transfusion, or treatment changes.

Keep reading