Glucose or HbA1c..Who you Gonna Call?
have the most instructive conversations with physicians and others outside of our
profession. Some day I would like to write a book of such conversations and recommend
its use as a discussion point for medical laboratory students. My friend the endocrinologist
was gushing to me about how wonderful HbA1c is. “I no longer order glucoses,”
logic was that glycosylated hemoglobin gives her a more accurate, realistic, long
term view of the patient’s glucose management. The patient does not have to be
fasting and she finds that she can “bust” patients who watch their diet meticulously
a few days before their visit, hoping she will see what she calls “a good number”
suggestive of better glucose management than really does exist.
wanted to know why “the lab” has not developed point of care HbA1c instruments for
use in clinics and medical offices. Why can’t she have that result when the patient
is in the office? I was explaining the state of the art technology available when a pathologist joined us.
endocrinologist recapped the discussion for the pathologist who immediately furrowed
his brow and declared that a glucose is still far superior to a HbA1c. Results from different
labs and even from different visits at the same laboratory are not comparable,
he said. HbA1c should ideally be used a few times per year for monitoring patient compliance with their medical regimen.
continued that glucose has ben around for ever, the technology is better and it
should always be used as the screen which then triggers a HbA1c. Besides, a physician
will only be reimbursed for ordering a HbA1c a couple times a year. I had no way
of verifying if that’s true or not, so I did not comment. But when he
launched into a discussion on the relative inaccuracy and imprecision of HbA1c compared to glucose,
and the merits of the oral glucose tolerance
test (OGTT) I sort of zoned out to protect my brain.
pathologist was an anatomical pathologist, not a clinical pathologist, which is an issue for an entirely different discussion. But the conversation and how it progressed got
me thinking about several things.
like this endocrinologist are very eager to discuss the use and relative merits of laboratory tests with the
experts-whether those are MLSs, pathologists, pharmacists or vendors pushing the newest black
Are pathologists, especially anatomical pathologists, really the right individuals to represent
the clinical laboratory as experts on what we do?
research after our talk indicated that fasting glucose variation can run around 8 percent In a single individual day over day, so
my pathologist friend was not entirely correct about how accurate/precise glucose
discovered that the American Diabetes Association (ADA) has been recommending that HbA1c be adopted
as an adjunct in the diagnosis of diabetes and prediabetes. Further, agencies
like the National Glycohemoglobin Standardization Program (NGSP) has done tremendous
work in standardization and controlling coefficient of variation among tests. Consequently, the accuracy and comparability of HbA1c have increased remarkably
in recent years.
discussions with clinicians need not be too technical. But we should remind them
when they ask about a new test or want a new point of care toy that as scientists
we need to look at aspects like ease of performance, specimen requirement, accuracy,
clinical utility, and positive or negative correlation with disease or disease risk.
-People tend to believe us if we speak with authority and have a history of not mis-speaking.
of family history and my own personal medical history I have a vested interest in how my physician uses and
interprets glucose and HbA1c, but more importantly, I want medical laboratorians
to be informed, to keep current, and to offer sound scientific guidance to clinicians. Nature abhors
a vacuum and if we are absent, all sorts of “experts” will jump in, often offering
information which is misleading at best.