What Is A1c?

Hemoglobin A1c (HbA1c) is a standardized clinical test used to diagnose and monitor type 1 and type 2 diabetes. Unlike a standard finger-stick test, which provides a snapshot of glucose at a single moment, A1c reflects your average blood sugar over the past three months.

Why “Hemoglobin A1c”?

Hemoglobin is the protein within red blood cells that carries oxygen. Glucose in the bloodstream is freely permeable to red blood cells and irreversibly attaches to hemoglobin. The higher the glucose levels, the more glucose binds to the hemoglobin.

Because the average lifespan of a red blood cell is approximately 120 days, measuring the percentage of glycated hemoglobin (A1c) provides an estimate of glucose control over the preceding three months.

Interpreting the Results: The A1c Conversion

A1c is reported as a percentage. Each 1% change in A1c reflects a 30 mg/dL change in average blood sugars.

Refer to the table below to convert A1c percentages into estimated average glucose (eAG):

Advantages of A1c Testing

• Standardization: It is a nationally and internationally standardized test, allowing clinicians globally to communicate effectively regarding diabetes control.

• Predictive Power: Large clinical studies indicate that every 1% improvement in A1c prevents diabetes complications by 30%. For example, reducing A1c from 10% to 7% reduces complication risk by roughly 90%.

• Convenience: No fasting is required. Recent food intake does not impact the result. In many outpatient settings, results are available within 5 minutes via a single finger prick.

Setting Your Goals

Diagnosis Criteria

• Prediabetes: A1c between 5.7% and 6.4%.

• Diabetes: A1c of 6.5% or higher.

Individualized Targets

While a general goal for many patients is below 6.5% or 7%, targets must be personalized. It is often unreasonable for an 85-year-old with a 20-year history of diabetes to target <6%, just as it is suboptimal for a healthy 30-year-old to target 7.5%.

Your endocrinologist will determine your goal based on:

• Life expectancy.

• Duration of diabetes.

• Risk of hypoglycemia (low blood sugar).

• Advanced complications (history of heart attack, stroke, kidney disease, neuropathy, or retinopathy).

Limitations and Nuances

The “Average” Trap

A1c represents an average, meaning it mathematically disregards extremes. A patient with blood sugars fluctuating wildly between 50 and 250 mg/dL may have the same average (150 mg/dL, or 7% A1c) as a patient with stable levels. While a 7% A1c is clinically superior to 9% (which suggests an average 60 mg/dL higher), the A1c alone does not reveal dangerous highs or lows.

Precision and Variance

All laboratory tests have a margin of error and a statistical confidence interval.

• Lab Variability: Results may differ slightly between your primary care office and your endocrinologist due to testing methodology.

• Repeat Testing: A sample testing at 6.9% might show a range of 6.5% to 7.3% if repeated immediately.

• Biological Variance: A reported A1c of 7% assumes an average of 150 mg/dL (the 50th percentile estimate), but the patient's actual real-world average could range from 120 to 180 mg/dL.

Interferences and False Results

Conditions that affect red blood cell turnover can skew A1c results:

• False Highs: Occur when red blood cell turnover is low.

• False Lows: Occur when red blood cell turnover is rapid (e.g., untreated anemia).

• Kidney Disease: Patients with severe kidney disease taking erythropoietin may show falsely low results.

• Hemoglobin Variants: Patients with sickle cell anemia or thalassemia may have falsely high values depending on methodology.

• Deficiencies: Iron deficiency, Vitamin B12 deficiency, and folate deficiency anemia can lead to misleading results.

Racial Considerations:

Racial differences influence the test’s estimation of blood sugar. A1c levels are typically higher in African-American, Hispanic, and Asian populations compared to Caucasians. While these differences generally do not lead to significant clinical problems, they are a factor to consider.

Pregnancy

A1c is helpful in early pregnancy to diagnose pre-existing diabetes, but it becomes less accurate as pregnancy progresses due to changes in hemoglobin and blood volume expansion. Endocrinologists typically rely on glucose tolerance tests, fingersticks, or Continuous Glucose Monitoring (CGM) during pregnancy.

Testing Frequency

Standard testing occurs every three months, as this matches the hemoglobin turnover cycle. However, 50% of the A1c change occurs within the first 30 days.

• More Frequent Testing: If an A1c improves by 1% in one month, it implies a potential improvement of another 1% to 1.5% over the next three months. This is useful for intensive therapy but may be limited by insurance coverage (e.g., Medicare typically limits testing to every three months).

Alternatives to A1c

When A1c is unreliable or insufficient, other markers may be used:

1. Fructosamine

Similar to A1c, but glucose attaches to serum albumin rather than hemoglobin. Because albumin turnover is faster, this reflects average glucose over 1 to 2 weeks. It is less reliable if the patient has protein-losing kidney or liver disease.

2. Glycomark (1,5-anhydroglucitol)

1,5-anhydroglucitol is a dietary polyol usually reabsorbed by the kidneys. When glucose spikes, kidney reabsorption is inhibited, causing levels of this substance to drop. Glycomark is excellent for detecting post-meal blood sugar spikes, which A1c may miss. It is often used as a complementary test.

3. Continuous Glucose Monitoring (CGM)

Systems like Dexcom, Freestyle Libre, or Medtronic provide real-time data. If your average glucose on a CGM is 150 mg/dL, you can safely assume an A1c of approximately 7%.

Troubleshooting: Why is my A1c stuck above 7%?

It is often easier to reduce A1c from 10% to 8% than it is to push from 8% down to 6.5%. If you are "stuck" between 7% and 8%, the barrier is likely post-meal blood sugar spikes.

To achieve an A1c below 7%, you generally need to meet these specific thresholds:

1. Fasting blood sugars: Less than 130 mg/dL.

2. 2-hour post-meal sugars: Less than 180 mg/dL at all times.

Once fasting numbers are controlled (<130), clinical focus must shift to maintaining the after-meal numbers using appropriate insulin or non-insulin medications.

The Bottom Line

Hemoglobin A1c is a vital tool for diagnosing and managing diabetes, reflecting a 3-month average of blood sugar control. While lower A1c levels correlate with fewer long-term complications, goals must be individualized based on patient health and hypoglycemia risk.

Success requires accountability. Patients who monitor glucose frequently, whether through fingersticks or remote monitoring systems, and communicate regularly with their specialists consistently achieve better outcomes. Intervening immediately to correct high blood sugars is the key to lowering A1c and preventing complications.

About The Author

Ahmet Ergin, MD, FACE, CDCES, ECNU About the author: Dr. Ergin operates a large diabetes practice mostly in West Palm Beach, FL, and yet can see diabetic patients across the entire state of Florida via a unique telehealth platform which also allows him to track patient progress and be available at all times. Soon to be available in NY and NJ. 2260 Palm Beach Lakes Blvd Ste 212 unit 7 West Palm Beach, FL