Efficacy of HbA1c Results Questioned; CGM is the New Standard, Claim Experts

WHILE HbA1c tests have been considered the gold standard for years, these tests do not necessarily correlate to good diabetes control. But HbA1c is only an average of glucose levels over time. A person can have major highs and lows every day, yet still have a “good” HbA1c level.

This is one reason why recent clinical trials reveal that HbA1c tests alone do not necessarily correlate to good diabetic control. It is also important to know that the more often you are outside your target range, the higher your risk of diabetes-related complications.

Indeed, there are many diabetics who experience hypoglycemia and hyperglycemia so often that they no longer realize when they have symptoms. Large-scale studies have shown, over time, these glycemic excursions cause major complications to the vascular system and organs.

Writing on his Endocrine Today blog, Michael Kleerekoper, MD, MACE wonders whether HbA1c is a reliable measure of glycemic control in an individual patient. His answer is: “It depends.”

As far as I can gather, the HbA1c is reliable in patients with fairly stable home blood glucose values, but too few patients measure blood glucose often enough to know this. It’s not the patient’s fault — their insurance carrier is very niggardly about the number of times a day a patient is allowed to measure blood sugar. If only the carrier would recognize the longer-term health care costs in those patients! All too often the patient leaves the glucose meter at home — that’s like going to the pediatrician without the baby.

Serial HbA1c is far less reliable in patients with widely fluctuating blood glucose values. Continuous glucose monitoring (CGM) is being utilized more frequently to document widely fluctuating blood glucose values, and patients learn a lot from the graphical illustration of how well or not well they are taking care of their diabetes.

Point-of-care HbA1c instruments are available and are also being used more often in the clinic. It makes sense to have the data available while the patient is still in the clinic rather than wait 24 hours for the lab result to come back.

Caveat emptor! If you are of a mind to get a handheld HbA1c device for your clinic, I encourage you to first read the editorial and article published in Clinical Chemistry about 1 year ago. Only two of the eight available devices were reliable!

Kleerekoper’s reservations bring us back to the question posed in the headline of this article: Are HbA1c results reliable enough?

Goals of Diabetes Self-Management

Basically, the goal of diabetes self-management is to help patients optimally manage their diabetes based on:

• Individual needs

• Customized goals

• Personal lifestyle considerations

So, do diabetics stick with the old fingerstick monitoring or shift to continuous glucose monitoring (CGM)?

Improving Diabetes Management

Over a decade ago, a landmark study called the Diabetes Control and Complications Trial — the largest study of its kind — revealed the importance of good glucose control. New, large-scale studies are revealing even more improvements in glucose control with the use of CGM technology.

In a recent study, people who were considered to be in “good control” showed distinct improvements in time spent within their target zone while using a CGM device. And subjects who were considered to be in “poor control” before the study, had even more impressive improvements with a 70% increase in time they spent in their target zone.

A recent study by the Juvenile Diabetes Research Foundation showed that using a CGM, for at least 6 days a week can lead to significant decreases in HbA1c and can provide a greater ability to reach the ADA recommended goal of 7%.

Revealing Unnoticed Highs and Lows

A CGM device can call attention to highs and lows that you may often experience, but not recognize. Sometimes people have “hypoglycemia unawareness” — they no longer feel their symptoms of going low. And some people are also unable to feel symptoms of high glucose. Over time, frequently swerving outside of your target range can lead to severe consequences, such as damage to your nerves, eyes, kidneys, and other organs.

Fingerstick vs. CGM: Revealing Unnoticed Highs & Lows

Recent studies reveal that fingerstick testing alone does not provide enough information to stay within their target range — even people who monitor frequently. In contrast, the use of a CGM device does a better job of helping people to stay between the lines. Indeed, CGM, especially in conjunction with HbA1c, helps to show a more complete picture of glucose control.

Real-Time Trending = 288 Fingersticks!

Fingerstick monitoring alone does not provide enough information for patients to act preemptively to avoid hyper- and hypoglycemic events. A major benefit of CGM is that it can help patients identify fluctuations and trends that would otherwise go unnoticed with standard fingerstick testing.

A CGM measures glucose levels and sends a glucose value every 5 minutes from the Transmitter to the Receiver. This is equivalent to a patient taking 288 fingerstick readings daily. However, unlike fingersticks, patients see real-time trending of glucose levels and patterns.

A CGM system shows patients their current glucose value, as well as their glucose trend over the past several hours (1-, 3-, 6-, 12-, and 24-hour trends). It also tells them how quickly their glucose is changing. And when glucose levels go above or below the set target range, alerts notify patients so they are able to take corrective action before going too low or too high — helping them stay between the lines.

Damage Caused By Glucose Variability

There is a growing body of clinical evidence showing that glucose variability itself — independent of HbA1c — initiates a cascade of physiological damage. Over time, hyper- and hypoglycemic events significantly increase the risk of diabetic complications, such as retinopathy and general microvascular pathogenesis, at least partially due to increases in oxidative stress and pro-inflammatory cytokines that are triggered by hyper- and hypoglycemic swings.

A CGM device can call attention to dangerously low overnight glucose levels that often go undetected, reveal previously unnoticed hyperglycemia spike trends between meals, show early morning highs in glucose, clarify the way diet and exercise affect your patients’ glucose levels and provide a long-term comprehensive assessment of the effects of adjustments in diabetes management.

It is not surprising, therefore, that in recent years CGM has gained acceptance among diabetes experts as an effective tool for helping people achieve their diabetes goals:

• Achieve HbA1c targets without adding hypoglycemia

• Reduce glucose highs and lows

• Reduce hypoglycemia

Indeed, when using a continuous glucose monitoring (CGM) device, study results demonstrate that the patients were actually experiencing extensive fluctuations in glucose levels. CGM, especially in conjunction with HbA1c, helps to show a more complete picture of glucose control.

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