How do hemoglobinopathies such as sickle‑cell disease, HbC, HbE, HbD, α‑ or β‑thalassemia, and hereditary persistence of fetal hemoglobin affect the accuracy and interpretation of HbA1c (glycated hemoglobin) measurements?

HbA1c Accuracy in Hemoglobinopathies

Hemoglobinopathies significantly compromise HbA1c accuracy, and in patients with homozygous variants (HbSS, HbEE) or compound hemoglobinopathies, HbA1c cannot be reliably measured and should not be used—alternative markers like fructosamine or glycated albumin must be employed instead 1.

Key Principle: Method-Dependent and Variant-Specific Interference

The impact of hemoglobinopathies on HbA1c varies by both the specific variant and the assay method used. Understanding this relationship is critical for accurate diabetes management.

Homozygous Variants (Most Severe Impact)

In patients with homozygous hemoglobin variants (HbSS, HbEE), HbA1c cannot be measured because HbA is absent 1. These patients require alternative glycemic markers:

• Fructosamine or glycated albumin are the recommended alternatives 1
• All standard HbA1c methods fail in this context 2, 3
• Case reports confirm that HbA1c appears falsely low or undetectable, masking severe hyperglycemia and diabetic complications 4, 5

Heterozygous Variants and Thalassemias

Heterozygous variants (HbAS, HbAE, HbAC, HbAD) and thalassemias produce method-dependent errors:

• Ion-exchange HPLC methods show significant positive bias in β-thalassemia 3 and variable results with HbE trait 3
• Immunoassay methods may give falsely low results in sickle cell trait and other variants 6, 7
• Capillary electrophoresis (e.g., Capillarys 2 Flex Piercing) demonstrates superior accuracy across most variants, detecting hemoglobin variants while providing more reliable HbA1c measurements 3
• Boronate affinity chromatography shows better agreement with reference methods in heterozygous variants 3

Red Blood Cell Turnover Effects

Any condition shortening RBC survival falsely lowers HbA1c regardless of assay method 1:

• Sickle cell disease (chronic hemolysis)
• α-thalassemia and β-thalassemia (increased RBC turnover)
• Recovery from acute blood loss
• Hemolytic anemia of any cause

This physiological interference occurs because HbA1c reflects average glycemia over the RBC lifespan (normally 8-12 weeks). Shortened RBC survival means less time for glycation, producing falsely reassuring results even with severe hyperglycemia 4.

Clinical Algorithm for Managing HbA1c in Hemoglobinopathies

Step 1: Identify At-Risk Populations

Screen for hemoglobinopathies in populations with high prevalence (African, Mediterranean, Middle Eastern, Southeast Asian ancestry) before relying on HbA1c for diabetes diagnosis or monitoring 2.

Step 2: Recognize Warning Signs

• Discordant HbA1c values between different assay methods 6, 7
• HbA1c inconsistent with fasting glucose or clinical presentation 4
• Abnormal chromatogram patterns 7
• Known anemia or abnormal RBC indices

Step 3: Laboratory Approach

When hemoglobinopathy is suspected:

• Perform hemoglobin electrophoresis or HPLC hemoglobin variant analysis 2
• Consider genetic testing for "silent" variants that don't appear on routine electrophoresis 7
• Use alternative assay methods (capillary electrophoresis preferred if available) 3
• Laboratories must be aware of potential interferences and select methods appropriate for their patient population 1

Step 4: Alternative Glycemic Monitoring

For patients with confirmed hemoglobinopathies affecting HbA1c:

• Use fructosamine or glycated albumin (reflects 2-3 weeks of glycemic control) 1
• Rely on fasting plasma glucose and glucose monitoring 1
• Consider continuous glucose monitoring for comprehensive assessment
• Document the specific hemoglobin variant and assay limitations in the medical record

Critical Pitfalls to Avoid

1. Never assume HbA1c is accurate in patients with hemoglobinopathies without verification 1—falsely low values can mask dangerous hyperglycemia and delay diabetes diagnosis 4

2. Don't switch between assay methods without recognizing potential discordance 6—a patient may appear well-controlled on one method and poorly controlled on another

3. Iron deficiency anemia falsely increases HbA1c 1, creating the opposite problem—this can coexist with hemoglobinopathies

4. Mass spectrometry measures total glycation across both α and β chains and is not impacted by hemoglobin variants 8, representing the most accurate method when available, though not widely accessible in routine practice

5. Hereditary persistence of fetal hemoglobin (HPFH) can interfere with some immunoassay methods due to HbF interference 5

Method Selection Guidance

Laboratories should prioritize:

• Capillary electrophoresis systems for populations with high hemoglobinopathy prevalence 3
• Boronate affinity methods as alternatives to ion-exchange HPLC 3
• Mass spectrometry when available for definitive measurement 8
• Avoid sole reliance on ion-exchange HPLC in diverse populations 3

The guideline explicitly states that laboratories must consider potential interferences in their particular patient population when selecting assay methods 1, making this a systems-level quality issue, not just an individual patient concern.