What Is the HbA1c Test and Why Do Hemoglobin Variants Cause Problems?

The HbA1c (glycated hemoglobin) test is one of the most widely used tools for diagnosing diabetes and evaluating long-term glycemic control. As blood glucose remains elevated, glucose molecules attach to hemoglobin inside red blood cells—a process known as glycation. The most clinically relevant form is HbA1c.

However, the accuracy of HbA1c can be compromised when a patient carries a hemoglobin variant. These variants can interfere with measurement methods and lead to misleading results. This article explores how HbA1c works, why variants matter, and how clinicians should approach interpretation.

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🧪 1. What Does the HbA1c Test Measure?

✔ A marker of average blood glucose over 2–3 months

Red blood cells have a lifespan of approximately 120 days. Because glycation occurs gradually, HbA1c reflects the average glucose concentration over the previous 2–3 months, making it one of the most reliable indicators of long-term glycemic control.

✔ A globally standardized test

HbA1c values are standardized by two major organizations:

• IFCC (International Federation of Clinical Chemistry)
• NGSP (National Glycohemoglobin Standardization Program, USA)

Standardization ensures that HbA1c results are comparable across laboratories worldwide.

✔ Diagnostic criteria for diabetes

According to most international guidelines:

• ≥ 6.5% → Diagnostic for diabetes
• 5.7–6.4% → Prediabetes

Because of its stability and clinical relevance, HbA1c is used not only for diagnosis but also for setting long-term treatment goals.

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⚠️ 2. What Is a Hemoglobin Variant and Why Does It Affect HbA1c?

HbA1c testing assumes that the patient has normal hemoglobin (HbA).
However, many individuals carry genetic variants of hemoglobin, which can alter the structure of the molecule.

📌 Common hemoglobin variants include:

• HbS (associated with sickle cell disease)
• HbC
• HbE
• Thalassemia mutations (α or β)
• Other rare variants (HbD, HbG, etc.)

Due to global migration patterns, hemoglobin variants are now found in a wide range of populations—including individuals in East Asia, the Middle East, and South Asia.

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❗ 3. Why Do Hemoglobin Variants Alter HbA1c Results?

Different laboratory methods measure HbA1c in different ways, and hemoglobin variants can interfere with these methods.

✔ 1) HPLC (High-Performance Liquid Chromatography)

HPLC separates hemoglobin components into peaks. Variants may cause:

• Abnormal or unexpected peaks
• Misidentification of the A1c peak
• Co-elution of variant peaks with HbA1c

➡ This may result in falsely low or high HbA1c values.

✔ 2) Immunoassay methods

Antibody-based assays detect the glycated N-terminal of hemoglobin. If a mutation alters this region:

• The antibody may fail to bind
• The value may appear lower than expected
• In some cases, measurement may fail completely

✔ 3) Changes in red blood cell lifespan

Many hemoglobin variants—such as those in thalassemia—affect RBC survival.

• Shorter lifespan → Falsely low HbA1c
• Longer lifespan → Falsely high HbA1c

This occurs regardless of actual glucose levels.

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🚨 4. Clinical Problems Caused by Variant-Related HbA1c Interference

When HbA1c is inaccurate, several clinical issues arise:

❗ (1) Misdiagnosis of diabetes

A patient may be labeled “diabetic” solely because the HbA1c reads falsely high.

❗ (2) Inappropriate adjustment of medication

Patients with stable glucose levels may have:

• Unnecessary insulin dose increases
• Unneeded medication changes
• Unwarranted intensification of therapy

❗ (3) Confusion in assessing complications or long-term control

If HbA1c is misleading:

• Treatment goals become inappropriate
• Risk assessment becomes unclear
• CGM/Self-monitoring data conflicts with HbA1c

Such discrepancies should always raise suspicion for a hemoglobin variant.

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🧭 5. How Should Clinicians Handle Variant-Related Issues?

✔ 1) Suspect interference when results do not match clinical findings

Red flags include:

• Abnormal HPLC chromatogram
• Sudden or extreme changes compared to previous results
• Discordance with glucose logs or CGM data
• HbA1c that seems “too low to be true”

✔ 2) Use alternative markers of glycemic control

When HbA1c is unreliable:

• Fructosamine
• Glycated albumin (GA)
• Continuous Glucose Monitoring (CGM)

GA is often the most useful alternative in patients suspected of hemoglobin variants.

✔ 3) Confirm with hemoglobin analysis when needed

• Hemoglobin electrophoresis
• Genetic testing for hemoglobinopathy

These tests help identify the specific variant causing interference.

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🔍 6. How Laboratories Manage HbA1c Variant Interference

Clinical laboratories typically:

• Review HPLC chromatograms for abnormal peak patterns
• Report unexpected peaks and notify clinicians
• Compare immunoassay vs. enzymatic methods when discordant
• Recommend retesting or alternative markers when variant interference is suspected

Clinicians should always reconsider HbA1c accuracy when patient symptoms and glucose profiles do not match laboratory results.

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📚 References

• Little RR, Rohlfing CL, Sacks DB. The National Glycohemoglobin Standardization Program: Over 20 years of improving HbA1c measurement. Clin Chem. 2019.
• Weykamp C. HbA1c: A review of analytical and clinical aspects. Ann Lab Med. 2013.
• NGSP. Factors That Interfere with HbA1c Test Results.
• Higgins T. Hemoglobin variants and interference in HbA1c measurement. Clin Chem Lab Med. 2012.
• American Diabetes Association. Standards of Medical Care in Diabetes.