Jan 24, 2011
About 24 million Americans, or 8 percent of the U.S. population, have diabetes. Although people with diabetes are at risk for serious medical complications, with close monitoring and treatment they need not suffer from them. The problem is 1 in 4 people with diabetes don’t even know it.
Compared to many other diseases, diabetes can be diagnosed easily. In people without any symptoms of the illness, two routine blood tests can provide the diagnosis. The first is to screen for the disease; if abnormal, the test is repeated. The most commonly used screening test for diabetes is a fasting plasma glucose test, or FPG. Because diabetes is characterized by abnormally high sugar levels in the blood (also called plasma), an FPG of 126 mg/dl or higher is suggestive of the condition.
While this sounds simple enough, diagnosing diabetes can be more challenging in practice. The problem with FPG is that it requires not eating anything for at least 8 hours prior, which is typically done by having the patient return on another day after skipping breakfast. This creates at least two barriers. First, for many patients coming to the doctor is an ordeal. My patients often have to take time off of work to see me. This is particularly true for those with blue-collar jobs that require them to report to work early in the morning, the exact time that the blood sample must be drawn. The second barrier is that returning for labs makes follow up more difficult. It is easier for doctors to keep track of tests that are done in the same office visit than those done later. As I discussed in a previous entry (http://beyondapples.org/2009/07/30/forgetting-to-break-bad-news/), studies show that over seven percent of clinically significant abnormal test results are not reported back to patients.
New recommendations from the American Diabetes Association (ADA) support the use of a new screening test, hemoglobin A1c (HbA1c), that promises to make the process easier.(1) HbA1c avoids the pitfalls above because it does not require an overnight fast. Blood glucose levels change moment-to-moment with food, stress, and time of day; in contrast, HbA1c is a measure of a person’s average blood sugar levels over the previous two to three months. As a “running average,” it is less subject to daily variation and is already being used to monitor people with diabetes. An HbA1c of 6.5% or higher is suggestive of diabetes.
Another advantage of HbA1c is that it allows doctors to more reliably diagnose diabetes in hospitalized patients. Any illness creates a sympathetic “fight-or-flight” response that drives up heart rate, blood pressure, and, it turns out, glucose levels. As a result, a patient who has an elevated FPG in the hospital may have diabetes or just be hyperstimulated. With HbA1c, doctors will be able to detect diabetes in those who are often at greatest risk of having it — those who slip through the cracks of good primary care and wind up in the hospital.
So should you be screened for diabetes? The United States Preventive Services Task Force (USPSTF) recommends routine screening for diabetes in individuals with a blood pressure above 135/80 mmHg.
(2) The ADA casts a wider net and recommends screening in all adults ages 45 and older, and younger adults who are overweight (body mass index or BMI > 25kg/m2) and have any additional risk factors:
* physical inactivity
* first-degree relative with diabetes (parents, siblings, children)
* members of a high-risk ethnic population (e.g., African American, Latino, Native American, Asian American, Pacific Islander)
* women who delivered a baby weighing > 9 lbs or were diagnosed with gestational diabetes
* hypertension (> 140/90 mmHg or on therapy for hypertension)
* HDL cholesterol level 250 mg/dl
* women with polycystic ovary syndrome
* other clinical conditions associated with insulin resistance (e.g., severe obesity, acanthosis nigricans)
* history of cardiovascular disease
To calculate your BMI, go to http://www.nhlbisupport.com/bmi/.
Like FPG, HbA1c can also help identify individuals with pre-diabetes, those with sugar levels that are abnormal but not enough to diagnose diabetes. For FGP, individuals with a blood sugar level of 100-125 mg/dl have pre-diabetes; with HbA1c the range is 5.7%-6.4%. One-third of people with pre-diabetes will develop diabetes within 3 years; recognizing the condition is critical because studies show that through aggressive lifestyle modifications people with pre-diabetes can prevent the onset of diabetes (see http://beyondapples.org/2009/11/14/world-diabetes-day-2009/).
Why go through all this trouble to talk about a new test for diabetes? After all, isn’t your doctor the one who decides whether to order blood work and what tests to order? The trouble is that we’ve learned the hard way that it takes anywhere from 7 to 10 years for the medical community to adopt a new guideline. For those of us at risk for diabetes that’s not soon enough. The next time your doctor orders blood work ask him or her about getting screened for diabetes. If you don’t need fasting blood work for another reason and are worried about having to come back, ask about HbA1c.
- Shantanu Nundy, M.D.
(1) Standards of Medical Care in Diabetes — 2010. American Diabetes Association. Diabetes Care, Volume 33, Supplement 1, January 2010.