What can cause a falsely elevated HbA1c and how should it be evaluated?

Falsely Elevated HbA1c: Causes and Evaluation

Iron-deficiency anemia is the primary condition that causes falsely elevated HbA1c, while hemoglobin variants and certain assay interferences can also produce spuriously high results depending on the measurement method used. 1

Key Causes of Falsely High HbA1c

Hematological Conditions

• Iron-deficiency anemia is specifically reported to increase HbA1c test results 1
• Prolonged red blood cell lifespan (>66.7 days) allows more time for hemoglobin glycation, resulting in falsely elevated values even with normal glucose levels 2
• Hemoglobin variants can cause method-dependent false elevations:
  • Some variants (e.g., Hb Graz, Hb Rainier) produce falsely high results on HPLC methods 3, 4
  • Certain variants elevate HbA1c across multiple measurement platforms including immunoassays 2

Assay-Specific Interferences

The 2023 ADA guidelines note that older literature reported false elevations with:

• Hypertriglyceridemia
• Hyperbilirubinemia
• Uremia (though this interference has been eliminated in modern methods)
• Chronic alcoholism
• Chronic salicylate ingestion
• Opiate addiction 1

Important caveat: These interference studies are dated and may not apply to current assay methods 1.

Patient-Related Factors

• Age: HbA1c increases approximately 0.1% per decade after age 30, even in non-diabetic individuals 1
• Race: Black individuals have mean HbA1c values 0.4% higher than White individuals, independent of glucose levels 1

Evaluation Algorithm

Step 1: Verify Discordance

When HbA1c appears elevated but doesn't match clinical picture:

• Check fasting plasma glucose and/or random glucose values
• Review self-monitored blood glucose data if available
• Consider continuous glucose monitoring (CGM) metrics including Time-in-Range, Glucose Management Indicator 5, 6

Step 2: Targeted Laboratory Testing

Order the following based on clinical suspicion:

For all discordant cases:

• Complete blood count with indices (MCV, MCH)
• Iron studies (ferritin, serum iron, TIBC, transferrin saturation)
• Reticulocyte count

If anemia or unexplained discordance:

• Hemoglobin electrophoresis or capillary electrophoresis 3, 4
• Consider beta-globin gene sequencing if electrophoresis is normal but suspicion remains high 3

Alternative glycemic markers:

• Fructosamine or glycated albumin (reflects 2-3 weeks of glycemia) 1
• These are particularly useful when RBC turnover abnormalities are present

Step 3: Method Verification

• Retest HbA1c using a different analytical method (e.g., if initial test was HPLC, use immunoassay or enzymatic method) 4
• Laboratories should use only NGSP-certified methods traceable to DCCT reference 1
• Be aware that some hemoglobin variants cause false elevations across multiple platforms 2

Step 4: Sample Handling Review

• Verify proper sample collection and storage (whole blood stable 1 week at 4°C) 1
• Improper storage at high temperatures can introduce artifacts 1
• Consider recollection if preanalytical error suspected

Critical Clinical Pitfalls

Do not reflexively intensify diabetes treatment based on elevated HbA1c alone when:

• Patient reports frequent hypoglycemia 2
• Self-monitored glucose values are consistently normal
• Clinical presentation doesn't match HbA1c severity
• Patient has known iron deficiency or anemia 7

The negative correlation between HbA1c and actual glycemia in anemic patients means that treating to HbA1c targets can lead to dangerous hypoglycemia 7.

When HbA1c Cannot Be Used

HbA1c cannot be measured and should not be reported in individuals with homozygous hemoglobin variants (HbSS, HbEE) 1. Use fructosamine or glycated albumin instead.

For conditions affecting RBC turnover (hemolytic anemia, recent blood loss, pregnancy), HbA1c provides spurious results regardless of method—glucose testing is necessary for diagnosis and management 1.

Practical Management Approach

When falsely elevated HbA1c is confirmed:

• Use alternative monitoring: Fructosamine, glycated albumin, or CGM metrics 1, 6
• Treat iron deficiency if present—this may normalize HbA1c-glucose concordance
• Document the interference in the medical record to prevent future misinterpretation
• Communicate with laboratory to flag the patient for alternative testing methods 3

The key is recognizing that HbA1c, while generally reliable, has well-defined limitations that require clinical judgment and confirmatory testing when results don't align with the broader clinical picture.