Recently I have been contacted by quite a number of friends and relatives, all wanting to know what I think their recent diabetes screening test results mean. Today, I want to focus on three questions: how diabetes is diagnosed; what prediabetes is; and whether it is important to know if someone has prediabetes or diabetes.
A Few Basics
First off, what is diabetes? Of course what I am referring to is diabetes mellitus, or “sugar diabetes,” not diabetes insipidus, a condition that causes increased urination because of an inability to concentrate the urine. The term “diabetes” is used describe a large number of distinct medical disorders, all of which have 3 things in common: insulin deficiency, hyperglycemia (high blood glucose levels) , and increased risks for the development of numerous complications, including diseases of the heart and blood vessels, the eyes, kidneys, and nerves. The insulin deficiency could be absolute, as is the case in patients who have auto-immune destruction of the cells in the pancreas that synthesize insulin- this is called type 1 diabetes, or T1DM. Alternatively, the deficiency can be resistance to the action of insulin, or a combination of the two mechanisms- this is called type 2 diabetes, or T2DM. T1DM and T2DM account for well over 90% of diabetes cases in the U.S., most of which are classified as T2DM. As an aside, sometimes it can be hard to tell whether a patient has T1DM or T2DM. But the basic treatment goals are the same for both types of diabetes.
The prevalence of diabetes in the U.S. is extraordinarily high: in 2014 it was estimated that almost 30 million people (9.3% of the total population) had diabetes and about 8 million of them didn’t even know it. Most of the diabetes was T2DM, a condition that is uncommon in people less than 20 years of age. The onset of T2DM is age-dependent; in people ages 20-44 years, the prevalence of diabetes was 4.1%, but in people age 65 years and greater, the prevalence was a whopping 25.9%. By comparison, in people less than 20 years of age, the prevalence of diabetes was low, accounting for only about 200,000 total cases, of which 75% were classified as T1DM.
Unfortunately, in addition to being a very common health concern, people with diabetes have a number of co-existing medical conditions, and often develop a wide variety of serious complications. For example, about 70% of people with diabetes have been diagnosed with high blood pressure; 65% have elevated blood cholesterol levels; people with diabetes have almost twice the death rate for cardiovascular diseases as do people without diabetes; almost 30% have diabetes-related eye disease (diabetes is the most common cause of non-traumatic blindness in the U.S.); diabetes is the cause of 44% of all new cases of kidney failure and the most common reason for kidney transplantation; and, diabetes is the most common cause of non-traumatic limb amputation. I could go on and on. Of course, all of these health problems cost plenty, in terms of dollars and misery; it is estimated that in the U.S. we spend about $200 billion annually on diabetes care costs- about 1 in every 10 dollars spent on health care in the U.S. These are staggering statistics.
What Can We Do About this Problem?
There are plenty of things we can do to improve upon these awful statistics. Many cases of T2DM can be prevented, mostly through regular exercise and weight control, and we already know how to prevent most of the complications in people who already have diabetes. We just haven’t done a very good job at getting the word out to both people with diabetes, and those at high risk for developing diabetes. In addition, data suggest that we have also not gotten the word out to many health professionals; the U.S. Centers for Disease Control and Prevention estimates that almost half of U.S. adults with diabetes do not meet the recommended goals for diabetes care (Ali MK et al: Achievement of goals in U.S. diabetes care, 1999-2010. N Engl J Med 2013;368:1613-24). In my opinion, the first step is to make sure all health professionals know it is important to determine if their patients have diabetes, or if they are at high risk for developing diabetes.
How To Diagnose Diabetes
According to the American Diabetes Association, there are 4 ways to diagnose diabetes: 1) In a patient with “classic” symptoms of hyperglycemia (high blood glucose), a random plasma glucose 200 mg/dl or greater. It is important to note that we throw around the term “blood glucose,” but what we really mean is plasma glucose; actual blood glucose is about 15% lower than plasma glucose, but is rarely measured in laboratories. Glucose meters, read blood glucose, but report values as if they were really plasma glucose. Anyway, the best known of the classic symptoms of hyperglycemia are increased thirst and increased urination. Normal fasting plasma glucose is about 60 mg/dl t0 90 mg/dl: 2) Fasting plasma glucose 126 mg/dl or greater. Fasting means no caloric intake over the previous 8 hours. 3) 2-hour plasma glucose 200 mg/dl or greater during an oral glucose tolerance test (OGTT). In my opinion, the OGTT is a nasty test in which the victim ingests a sugary drink containing 75 grams of glucose (this is equivalent to about 15 teaspoons of sugar), and has multiple blood specimens collected over 2-5 hours for measurement of plasma glucose. Except for research studies and for diagnosis of gestational diabetes, I can’t think of any reason to ever do an OGTT. The test is expensive, cumbersome, unpleasant, and is not very reproducible. 4) Hemoglobin A1c (HbA1c) 6.5% or greater. The ADA recommends that this test be performed only in a laboratory using a method that is NGSP certified and standardized to the DCCT assay. Following these guidelines is the best way to insure that the test has been performed properly. HbA1c is a simple blood test that provides an estimate of a person’s average plasma glucose over the previous 2-3 months, and has been widely used for diagnosis of diabetes over the past 4-5 years. If you want to know more about HbA1c, or what the NGSP is, or what the DCCT is, you can check out one of my earlier entries or just “google” the terms. Finally, the ADA recommends that in the absence of unequivocal hyperglycemia, diagnostic tests 2-4 should be confirmed by repeat testing. Personally, I would recommend confirming the diagnosis by both repeating the test and doing one other diagnostic test. It is very important to know for certain that a person really does have diabetes before embarking on a difficult, and often expensive, treatment plan.
What About People at Increased Risk for Diabetes (Prediabetes)?
With so much diabetes around, the logical question is: who to screen for diabetes? Presumably, if a person presents to their health care professional with signs and/or symptoms suggestive of diabetes, testing for diabetes will be a high priority. But, what about people who exhibit no signs or symptoms suggesting diabetes? The ADA recommends the following approach to screening people for diabetes: test people who are overweight and have one or more additional risk factors for diabetes. These include the following: physical inactivity; first-degree relative with diabetes; high-risk race/ethnicity (e.g., African-American, Latino, Native American, Asian American, Pacific Islander); women who delivered a baby weighing more than 9 lbs or were diagnosed with gestational diabetes; hypertension; HDL-cholesterol level (the “good” cholesterol) less than 45 mg/dl and/or a triglyceride level greater than 250 mg/dl; women with polycystic ovary syndrome; HbA1c of 5.7% or greater (normal range is 4.3% to 5.7%); impaired glucose tolerance (2-hour post glucose tolerance test plasma glucose between 140-199 mg/dl, or fasting plasma glucose between 100 mg/dl and 125 mg/dl on previous testing; other clinical conditions associated with insulin resistance; history of cardiovascular disease. Finally, the ADA recommends that even for people who are not overweight or have specific risk factors for diabetes, screening should begin at age 45 years and be repeated at least every 3 years. I think these are very good recommendations. You may have noticed that the ADA has not recommended screening children for diabetes, unless they are adolescents and are overweight. This is because, most cases of diabetes presenting in childhood are T1DM. This disorder is relatively uncommon (the prevalence is about 1 in 750 children), and progress rapidly from prediabetes to diabetes, usually with classic symptoms. By comparison, studies have shown that many people eventually diagnosed with T2DM have actually had diabetes for quite a number of years, with without any obvious symptoms or signs; the average duration of T2DM prior to diagnosis is estimated to be 5-10 years!
So, Is It Important To Diagnose Prediabetes and Diabetes?
So, now we come to the critical question: is it important to diagnose prediabetes and diabetes? To some of you this might seem like an easy question to answer- you would say “no duh.” But, it is not so simple. Not so many years ago (I think it was about 1987), I participated in a debate over the following question: “Is it worthwhile to screen for diabetes?” By a toss of the coin, my assignment was to defend the benefits of screening, while my esteemed colleague, Dr. David Nathan, from Harvard Medical School, took the other side of the argument. I am quite certain that both of us knew in our hearts that screening for diabetes was worthwhile, but at the time there were no firm data to show that making a diagnosis of diabetes and treating the patient, made any difference with respect to outcomes (at the time, he and I were in the midst of a long-term N.I.H. study to determine -if well-controlled diabetes decreased patient risk for the development of diabetes chronic complications, but the results were not in, and would not be for another 5 or 6 years). I think the outcome of the debate ended up a draw.
But it is 2015, and things are much different now. Elegant studies have defined the risk factors for adverse outcomes in both T1DM and T2DM. By far the most important of these risk factors are glycemic control (as quantified by serial HbA1c measurements), blood lipid levels, and blood pressure. There can be no doubt that treating these risk factors results in dramatic reductions in the development and progression of diabetes complications. Yet, there are still skeptics. A few weeks ago, there was an interesting report in the NYT entitled: “With expansion of Medicaid, some states are identifying more new diabetes cases,” written by Sabrina Tavernise (NYT Monday, March 23,2015, pA14). The NYT article summarized a recent report in the medical journal, Diabetes Care, showing that many more people were being diagnosed with diabetes in states that had expanded Medicaid coverage as part of the Affordable Care Act than in states that did not expand Medicaid coverage. The NYT reporter contacted a number of diabetes experts to get their “take” on the study. All agreed that although the study was an observational one rather than a randomized controlled trial, the results were impressive. I was most interested in one of the expert’s comment that the results were interesting, but that there were really no data to show that diagnosing diabetes and treating people makes any difference on outcomes, particularly cardiovascular complications. Suddenly it was deja vu to 1987 and my “to screen or not to screen” debate. In my opinion, the data showing benefit from diabetes treatment are incontrovertible. But, we can’t treat people with diabetes until we know they have it.
The Bottom Line
We know how to prevent diabetes in many people who are at increased risk for T2DM. In people who already have diabetes, we know what the risk factors are for diabetes complications, and how to decrease them dramatically. We also know how to diagnose both prediabetes and diabetes. Shouldn’t this be a high priority for our health care system? I am not going to get into the political debate about the Affordable Care Act, but the Medicaid data I referred to above make clear that the first step is to make certain that all people have easy access to quality health care system. The second step is for all health care providers to screen at regular intervals all patients at increased risk for diabetes.
If you want to read more about this topic you might check out the following websites:
- That Lazy Dr. Goldstein
- Is “Prediabetes” A Disease?