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Have you recently had an HbA1c blood test? It is quite likely that at least once a year you will have one. It’s a common and important test that can measure your long-term average blood sugar levels.

This guide will help you interpret your HbA1c results, and explain why HbA1c is an important way to measure metabolic health. We’ll also explain reasons for occasional unexpected variations in HbA1c results and the strengths and weaknesses of the test.

What is HbA1c and why does it matter?

Hemoglobin A1c (HbA1c, or sometimes just called an A1c) is a way to assess your average blood glucose levels. It differs from a fasting glucose measurement in that fasting glucose is a snapshot of your blood glucose level at that one moment in time, when you first wake up in the morning before eating. The HbA1c, however, is a longer-term measurement that reflects your average blood sugar over the previous two to three months.

It can measure this longer time frame because hemoglobin, which transports oxygen in your blood, is a protein that glucose sticks to over time. The more sugar in your blood, the more it sticks to the hemoglobin. When any protein becomes sticky with sugar in this way it’s called glycation or glycosylation. So rather than measuring the amount of glucose in a drop of blood, HbA1c measures the percentage of glucose stuck to the hemoglobin in your blood, or in medical terms, the percentage of glycation of the hemoglobin.

How do you interpret HbA1c numbers?

HbA1c is an important measure because it can be used to diagnose type 2 diabetes or pre-diabetes. It can also be used to monitor how well you are managing your blood sugar levels if you have type 2 diabetes or pre-diabetes, especially if you’ve made changes to your diet and lifestyle.

The American Diabetes Association (ADA) uses the following cutoff points for HbA1c:

Normal: less than 5.7%

less than 5.7% Pre-diabetes: 5.7% to 6.4%

5.7% to 6.4% Type 2 diabetes: 6.5% or higher

A diagnosis of type 2 diabetes or pre-diabetes should not be made using only one measurement of your HbA1c. The test should be repeated to confirm that the results are consistent or it should be used in conjunction with a fasting blood glucose or an oral glucose tolerance test to confirm the diabetes diagnosis.

HbA1c and average blood glucose

HbA1c result can be translated into an estimated average daily glucose level. Here are the averages and ranges the ADA uses:



Maintaining blood sugar within a normal range is critically important for long-term health. Does that mean, however, that you’re totally fine if your level is consistently 5.6% or below? Not necessarily. When your HbA1c is bordering the cuttoffs for pre-diabetes, and your results are trending up, it can be an indicator that you are on your way to future blood sugar problems and perhaps an eventual type 2 diabetes diagnosis.

If your HbA1c is obviously quite high — regularly in the type 2 diabetes range— that is a clear indication that your blood glucose is elevated most of the time and you should explore ways to help bring it down to a healthier level, such as with a low-carb or ketogenic diet or intermittent fasting.

Why do low-carb diets often lower HbA1c?

Since HbA1c is an indicator of your long-term blood glucose level, it makes sense that strategies to lower your daily blood glucose levels would also lower your HbA1c. Low-carb and ketogenic diets are powerful ways to do this. If you are not eating sugar, or carbohydrates that rapidly digest to sugar, you won’t have excess sugar circulating in your blood.

Blood glucose may improve so quickly on a ketogenic diet that some people with type 2 diabetes need to reduce or discontinue their insulin on the very first day of adopting the diet. (Always work with a physician or other qualified medical professional for this. Do not adjust medications on your own.)

Low-carb and keto eating, however, aren’t the only ways to lower HbA1c. This can also be accomplished with a low-glycemic diet, intermittent fasting, and even by incorporating more exercise into your life without much of a change in diet.

Most of the research comparing low-carb and keto diets to other ways of eating, however, shows that carb restriction is more effective, and moreover, it’s effective even without exercise. In a study comparing different interventions in overweight individuals with type 2 diabetes, pre-diabetes, or metabolic syndrome, subjects who followed a ketogenic diet for 10 weeks (<30 g carbs per day) but did not exercise had much greater reductions in HbA1c than subjects who followed a standard American diet and exercised three to five days per week.

The American Diabetes Association recently issued a consensus report in which they acknowledged the effectiveness of low-carb and very low-carb diets for improving blood sugar control. The consensus panel noted that multiple meta-analyses have shown that these carbohydrate restricted ways of eating typically lower HbA1c results more than low-fat diets, although the differences tend to get smaller over time. This might not be because low-carb stops being more effective, but rather, because some people may have difficulty sticking to the diet after a while, so they may inadvertently start eating more carbs.

With regard to improving blood glucose control, and thereby improving HbA1c results, the ADA panel wrote: “reducing overall carbohydrate intake with low- or very low-carbohydrate eating plans is a viable approach.”