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Hemoglobin Abnormalities Affect A1c Testing

Nov 10, 2020
 

I recently saw a patient for a diabetes follow-up and had just gotten her lab values faxed over. Her A1c came back at 9.6, despite the patient telling me that her glucose meter readings were much lower. She even showed me the meter, and upon doing some averaging, it appeared that her A1c should be a lot lower.  

My first thought was a faulty meter, and so immediately we gave her another one, but upon first use, in the office, the glucose readings on each were 122 mg/dl and 128 mg/dl, respectively. I had her use the new meter for seven days and return. The readings on the meter indicated that her A1c should be in the 7.6 range. 

 

Upon further investigation, we found that the patient had the sickle cell trait hemoglobin variant. The endocrinologist in the office explained that this and other blood anemias could cause falsely elevated A1c readings, depending on the labs’ testing device. 

Sheryl K., RN, CDE  

Editor’s note: Blood disorders that affect A1c values are more common than we may think. These disorders can include sickle cell trait, thalassemia, and some forms of anemia.  Most heterozygous people have one variant gene and one normal hemoglobin gene — for a hemoglobin variant has no symptoms and patients may not know that they carry this type of hemoglobin. Health care providers should suspect the presence of a hemoglobinopathy when: 

  • An A1C result is different than expected 
  • An A1C result is above 15 percent 
  • Results of self-monitoring of blood glucose have a low correlation with A1C results 
  • a patients A1C result is radically different from a previous A1C result following a change in laboratory A1C methods 

According to the NGSP — The hemoglobin A1C (A1C) test can be unreliable for diagnosing or monitoring diabetes and prediabetes in people with inherited hemoglobin variants, also called hemoglobinopathies. Hemoglobins S and E are prevalent variants in people of African, Mediterranean, or Southeast Asian descent. These variants interfere with some A1C tests — both laboratory and point-of-care tests. If A1C tests are at odds with blood glucose testing results, interference should be considered. 

Reliable A1C tests that do not cause interference with hemoglobin variants are available. More information about appropriate assay methods to use for hemoglobin variants is available from the NGSP at www.ngsp.org 

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