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 The test known as hemoglobin A1c (HbA1c) estimates long-term blood
sugar levels by measuring the amount of glucose sticking to red
blood cells, but blood cells from people with sickle cell trait
don't live as long, so they have less time to collect glucose.
When lead author Mary Elizabeth Lacy from Brown University School of
Public Health in Providence, Rhode Island, and her colleagues used
standard HbA1c cutoffs to screen for diabetes, “we identified 40
percent fewer cases of prediabetes and 48 percent fewer cases of
diabetes in individuals with sickle cell trait than in those without
sickle cell trait,” she told Reuters Health by email.
Sickle cell disease is a serious condition that occurs when a person
has two copies of a defective gene responsible for making part of
the hemoglobin molecule in red blood cells. Hemoglobin allows the
cells to carry oxygen to the tissues that need it, but in people
with two copies of the faulty gene, blood cells can turn
sickle-shaped, causing painful crises and even death.
People with only one copy of the defective gene are said to have
sickle cell trait, and most have no symptoms of sickle cell disease.
The gene is most common among people with ancestry in sub-Saharan
Africa, Central America and South America, Saudi Arabia, India,
Turkey, Greece and Italy.
The U.S. Centers for Disease Control and Prevention estimates that 1
in 13 African American babies are born with sickle cell trait.
In their study of 4,620 African Americans, including 367 with sickle
cell trait, Lacy’s team found that HbA1c levels were 0.3 percent
lower in those with the trait than in those without it, even though
they had similar blood sugar levels.
While 0.3 percent may seem small, Lacy said, “a difference of 0.3
percentage points in HbA1c could be the difference between being
identified as high-risk (and being targeted for more frequent
monitoring as well as additional diabetes prevention efforts) or
not, or receiving a diagnosis of diabetes or not.”
Among individuals with no history of diabetes and not taking
diabetes medications, testing blood sugar directly detected
pre-diabetic elevated blood sugar levels or full-fledged diabetes in
equal numbers of people, regardless of whether they had sickle cell
trait, the researchers report in JAMA.
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But if HbA1c was used instead of blood sugar testing, pre-diabetic
elevated blood sugar would be diagnosed in about 29 percent of those
with sickle cell trait compared to 49 percent of those without the
trait. Similarly, the HbA1c test would identify diabetes in about 4
percent of those with sickle cell trait and about 7 percent of those
without the trait.
The results of HbA1c testing need to be interpreted with caution in
patients with sickle cell trait, Lacy concludes. “These findings
were based on one method of HbA1c measurement. While it is approved
for use in those with sickle cell trait, we are unable to say
whether our findings are due to assay interference or a biological
phenomenon in those with sickle cell trait.”
Doctors should consider using a glucose tolerance test if they
suspect diabetes in people with SCT whose HbA1c is close to the
cutoff level, said Dr. Anthony J. Bleyer from Wake Forest School of
Medicine in Winston-Salem, North Carolina, who coauthored a related
editorial.
“I think there needs to be more research in this area. The HbA1c is
a really important test that we use all the time. We need to make
sure it is accurate for individuals of all races and ethnicities,”
Bleyer said by email.
“Approximately 10 percent of African American patients have sickle
cell trait. It is prudent to test African American patients for
hemoglobinopathy (sickle cell trait) before relying on HbA1c for
diagnosis diabetes/prediabetes and before using HbA1c to monitor
blood sugar control,” Dr. Kristina Behan from the University of West
Florida in Pensacola, who was not involved in the study, said by
email.
SOURCE: http://bit.ly/2ln3Rap and http://bit.ly/2kovj9m JAMA, online
February 7, 2017.
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