A lab report may list blood glucose, A1C, or both. Knowing what each test measures can make the results easier to discuss at your next visit.
What each test measures
A fasting plasma glucose test measures the glucose in a blood sample at one point in time. Other glucose tests may involve more than one sample. A1C estimates your average blood glucose over roughly the past three months.
A1C is reported as a percentage. It measures the share of hemoglobin in your red blood cells that has glucose attached. The percentage summarizes an average; it does not tell you the glucose level at a particular moment or show the ups and downs in daily readings. An A1C percentage also is not a glucose meter reading, so the two numbers cannot be compared as if they were the same measurement.
Preparation and limits to keep in mind
A1C testing alone does not require fasting. Other tests ordered at the same appointment may require it. Before the test, ask the clinic which tests are being done and whether any require fasting, then follow its instructions.
Some conditions that affect red blood cells can affect A1C accuracy. If you have such a condition, tell your clinician and ask whether it matters when interpreting your result. Your clinician can consider this alongside the test and your medical history.
How to discuss results and next steps
Have the test names and dates available when you talk with your clinician. You can ask:
- What does this result mean in my situation?
- How does it fit with my other test results and medical history?
- Does it need to be confirmed, and what follow-up do you recommend?
For people without symptoms, an A1C result suggesting diabetes or prediabetes should be confirmed with repeat testing on a different day. The repeat test may use A1C or another diabetes test, and the clinician decides which test and follow-up are appropriate.
If you were asked to fast, you can mention whether you followed the clinic’s instructions. That information may help when you and your clinician review the results.