Diabetes cases on the rise: current diagnosis guidelines and research efforts for a cure

CONTINUING EDUCATION

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LEARNING OBJECTIVES

Upon completion of this article, the reader will be able to:

1. define diabetes and differentiate between type 1 and type 2 diabetes;
2. describe various aspects of insulin in relationship to diabetes;
3. list the guidelines for the diagnosis of diabetes; and
4. discuss various research efforts for the prevention and cure of type 1 and type 2 diabetes.

According to the American Diabetes Association (ADA), diabetes is defined as a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both.¹ When uncontrolled or untreated for lengthy periods of time, this devastating disease is associated with damage, dysfunction, and failure of different organs, especially the eyes, kidneys, nerves, heart, and blood vessels. Diabetes was the 7th leading cause of death in America in 2006; and according to death-certificate reports, diabetes contributed to a total of 233,619 deaths in 2005, the latest year for which data on contributing causes of death are available.² This number is likely to be higher, however, due to under-reporting of diabetes on death certificates, thereby underestimating the burden of the disease and the influence of diabetes on death rates.³ The risk for death among people with diabetes is about twice that of people without diabetes of similar age.² The purpose of this review is to discuss the predominant forms of diabetes and their prevalence, current guidelines for diagnosis, and ongoing research efforts for a cure.

Type 1 and type 2 diabetes

The term “diabetes” was coined by Aretaeus of Cappadocia around 100 AD. This Greek-derived term itself was formed from the prefix “dia,” meaning “across or apart,” and the verb “bainein,” meaning “to walk or stand.” Diabainein meant “to stride, walk, or stand with legs asunder.” The derived term “diabetes” meant “a compass or siphon,” which gave rise to its use as the name for a disease involving the discharge of excessive amounts of urine. In 1675, Thomas Willis, an English physician and researcher, added the word “mellitus,” from the Latin meaning “honey,” a reference to the sweet taste of the urine (glycosuria) observed in diabetics.

It is clear that diabetes has been around for centuries, and epidemiological data suggest it will only increase in prevalence if current trends continue. One in 10 U.S. adults has diabetes now. According to the Centers for Disease Control and Prevention (CDC) projections, diabetes’ prevalence is expected to rise sharply over the next 40 years due to 1) an aging population more likely to develop type 2 diabetes, 2) increases in minority groups that are at high risk for type 2 diabetes, and 3) people with diabetes living longer.⁴ As many as one in three U.S. adults could have diabetes by 2050.

Statistics from the most recent CDC National Diabetes Fact Sheet reveal a total of 23.6 million children and adults in the United States (7.8% of the population) have diabetes. For the majority of cases, diabetes can be grouped into two broad categories: type 1 and type 2. Type 1 diabetes is the least-prevalent category (5% to 10% of those with diabetes) and is usually diagnosed in children and young adults. This group was previously referred to as insulin-dependent diabetes mellitus or juvenile-onset diabetes. In type 1 diabetes, the body does not produce insulin. The lack of insulin production is due to autoimmune destruction of the betacells of the pancreas. Those at increased risk of developing this type of diabetes can often be identified by serological evidence of an autoimmune pathologic process occurring in the beta-cells and by genetic markers.¹

Markers of the immune destruction of the insulin-producing cells include autoantibodies to beta-cells themselves, insulin, GAD (GAD65), and the tyrosine phosphatases IA-2 and IA-2-beta. Usually, more than one of these autoantibodies are present in 85% to 90% of individuals when fasting hyperglycemia is initially detected.¹ The genetic factors HLA DQ and DR are found to be the most important determinants for type 1 diabetes risk.⁵ The specific haplotypes HLA-DQ A1*0301-B1*0302 or A1*0501-B1*0201 — accounting for up to 90% of children and young adults with type 1 diabetes — may be present, however, in 30% to 40% of the Caucasian population and, therefore, be necessary but not sufficient for disease.⁶ Genetic markers are currently of limited clinical value in the evaluation and management of patients with diabetes.

Several stages exist in type 1 diabetes. The stages begin with normal glucose regulation (normoglycemia), which precedes the event that triggers the immune system to attack the beta-cells of the pancreas. The rate of beta-cell destruction is variable, being rapid in some individuals (infants and children) and slow in others (adults). Residual beta-cell function can be sufficient to prevent ketoacidosis for many years in some patients with diabetes and may result in an impaired fasting glucose (hyperglycemia), which puts the individual at increased risk for diabetes. Type 1 diabetics eventually become dependent on insulin for survival. At this latter stage of the disease, there is little or no insulin secretion, as manifested by low or undetectable levels of plasma C-peptide, a byproduct of insulin production.¹

Type 2 diabetes is the most predominant form, accounting for 90% to 95% of those with the disease. Millions of people in the U.S. have been diagnosed with type 2 diabetes, and many more are unaware they have the disease or are at high risk. Type 2 diabetes is more common in African-Americans, Latinos, Native Americans, Asian-Americans, Native Hawaiians, and other Pacific Islanders. In addition, the risk of developing this form of diabetes increases with age, obesity, and lack of physical activity.¹ Most patients with this form of diabetes are obese; obesity itself causes some degree of insulin resistance. Obesity is associated with an increased risk of developing insulin resistance and type 2 diabetes. In obese individuals, adipose tissue releases increased amounts of non-esterified fatty acids, glycerol, hormones, pro-inflammatory cytokines, and other factors that are involved in the development of insulin resistance.⁷ The properties of visceral adipose tissue may cause these dysfunctions to become magnified.

Weight loss has the potential to improve insulin sensitivity through alterations in adipose-tissue function.⁸ Patients who are not obese by traditional weight criteria may have an increased percentage of body fat distributed primarily in the abdominal region.¹ The association between obesity and insulin resistance is largely due to changes in the function of adipose tissue, specifically, increased release of free fatty acids and abnormalities in adipokine secretion.⁸ Statistics from the CDC show the extreme increase in the prevalence of obesity from 1990 to 2001 in the U.S. has paralleled the increase in prevalence of diabetes.⁹

The stages that exist in type 2 diabetes are similar to that of type 1; however, in patients with type 2 diabetes, there is no autoimmune beta-cell destruction. People with type 2 diabetes produce insulin. The insulin they secrete, however, is not excreted in sufficient amounts, or the body is unable to recognize the insulin and use it properly. Type 2 diabetics do not become dependent on insulin for survival. At the latter stage of the disease, insulin secretion and/or action may be minimal.

Various forms of medications can be used to treat type 2 diabetes. These include alpha-glucosidase inhibitors that work to decrease the absorption of carbohydrates from the digestive tract to lower after-meal glucose levels. Biguanides (Metformin) acts on the liver to produce less glucose and help muscle, fat cells, and the liver absorb more glucose from the bloodstream, thereby lowering blood-sugar levels. Meglitinides and sulfonylureas act on the pancreas to produce more insulin in response to the level of glucose in the blood. Thiazolidinediones act on the liver to absorb more glucose when insulin is present.

Guidelines for diagnosis

The diagnostic criteria for diabetes have included the measurement of plasma glucose for years. There are some known disadvantages that exist, however, when using glucose as a criterion for diagnosis. If a fasting glucose is used, the patient must fast for at least eight hours — an unattractive choice because of the challenge for a physician or a laboratory to enforce or for a patient to adhere to. In addition, there is both intra- and inter-individual biologic variability that confound glucose-result interpretation.^10,11 This observed variability demonstrates that the concentration of a fasting individual’s glucose is not the same when measured on different days. Further, because fasting plasma glucose is higher in the morning than in the afternoon, this measurement may show even greater variability if samples are obtained at a different times of the day after the patient’s eight-hour fast.

There is also the issue of sample stability. It has been shown that in vitro glycolysis occurs in uncentrifuged whole blood for up to four hours, even in the presence of fluoride,¹² the recommended tube of choice when drawing blood for glucose testing. The mechanism of this action is 1) that when fluoride is mixed with blood, it rapidly blocks enolase, and 2) that enzymes upstream of enolase in the glycolytic pathway remain active. Glucose then continues to be metabolized to glucose-6-phosphate, which is further metabolized to other phosphorylated metabolites of glucose, all of which accumulate in the cells. The delay in fluoride’s ability to stop the use of glucose reflects continuing metabolism of glucose, despite inhibition of the downstream target enzymes inhibited by fluoride. Thus, the glucose concentration continues to decrease in the plasma.¹³ The rates of decline of glucose in the first hour after sample collection in tubes with and without fluoride are virtually identical, and glycolysis continues for up to four hours in samples containing fluoride. After four hours, the glucose concentration is stable in whole blood for 72 hours at room temperature in the presence of fluoride.¹⁴

For the diagnosis of diabetes, a fasting plasma glucose >=126 mg/dL (7.0 mmol/L) or a two-hour plasma glucose >=200 mg/dL (11.1 mmol/L) during an oral glucose-tolerance test must be observed and confirmed by repeat testing. Due to the variability of measuring glucose, as described above, the ADA recommends that a patient’s glucose value be confirmed on a subsequent day to make certain that the patient’s glucose value exceeded 126 mg/dL on more than one occasion. In a person with symptoms of hyperglycemia or hyperglycemic crisis, one random plasma glucose >=200 mg/dL (11.1 mmol/L) is sufficient for the diagnosis of diabetes.¹

In 2005, a survey of physicians demonstrated that 93.4% routinely screen for diabetes; and, interestingly, 49% reported using glycated hemoglobin (A1c) for screening and 58% for diagnosis of diabetes. Forty-nine percent also thought A1c was an approved test for screening.¹⁵ It was not until 2010 that the ADA’s guidelines for the Diagnosis and Classification of Diabetes Mellitus recommended the use of the A1c test to diagnose diabetes. A1c is currently a widely used marker of chronic glycemia, reflecting average blood-glucose levels over the previous two to three months, or the lifespan of a normal red blood cell (RBC).

According to the ADA, several advantages exist when using A1c as a diagnostic criterion; and it affirmed the decision of an International Expert Committee to use the A1c test to diagnose diabetes in non-pregnant adults. The main factors in support of using A1c as a diagnostic test include 1) A1c does not require patients to be fasting; 2) A1c reflects longer-term glycemia than does plasma glucose; 3) A1c laboratory methods are currently well standardized; and 4) errors caused by non-glycemic factors affecting A1c (e.g., hemoglobinopathies) are infrequent and can be minimized by confirming the diagnosis of diabetes with a plasma-glucose- (PG-) specific test.¹⁵ Important to note is that in cases where hemoglobinopathies preclude the use of a method to determine A1c, the fundamental component of A1c to manage diabetic patients or diagnose diabetes proves useless. This is especially true for diabetic patients where there is no HbA present (e.g., homozygous HbS, HbC, or for those with HbSC disease), as all A1c methods are inadequate for the assessment of long-term average blood glucose in these patients due to pathological conditions that affect the formation and turnover of RBCs.¹⁶ According to the 2010 ADA guidelines, for patients harboring a hemoglobinopathy but normal red-cell turnover (e.g., sickle-cell trait), an A1c assay without interference from abnormal hemoglobins should be used. For conditions that display abnormal red-cell turnover (e.g., anemias from hemolysis and iron deficiency), the diagnosis of diabetes must employ glucose criteria exclusively.

For the diagnosis of diabetes, an A1c >=6.5% must be observed and confirmed on repeat measurement. The diagnostic A1c cut point was set at 6.5% since above this value the prevalence of retinopathy increases significantly, as is observed with the diagnostic cut points for the fasting blood glucose and two-hour post-prandial glucose.¹ Currently, point-of-care A1c assays are not sufficiently accurate to use for diagnostic purposes.¹ The diagnostic test should be performed using a laboratory method that is certified by the National Glycohemoglobin Standardization Program.¹ There is not 100% concordance between A1c and either of the glucose-based diagnostic tests. When two different tests are available for an individual and the results are discordant, the ADA recommends that the test result that is above the diagnostic cut point be repeated and the diagnosis be made on the confirmed result.¹

Categories of increased risk for diabetes, such as impaired fasting glucose or impaired glucose tolerance (formerly referred to as pre-diabetes), is the phrase given to define blood-glucose levels that are higher than normal but below the level of a person with diabetes. This condition is a combination of impaired secretion of insulin and reduced insulin sensitivity (insulin resistance). These categories are associated with obesity (especially abdominal or visceral obesity), dyslipidemia with high triglycerides and/or low HDL cholesterol, and hypertension. These conditions together can be associated with metabolic syndrome, a condition that is associated with risk of cardiovascular disease and diabetes. For the diagnosis of increased risk for diabetes, a fasting plasma glucose concentration between 100 mg/dL (5.6 mmol/L) and 125 mg/dL (6.9 mmol/L), a glucose concentration between 140 mg/dL (7.8 mmol/L) and 199 mg/dL (11.0 mmol/L) two hours after a 75-gram oral glucose-tolerance test, or an A1c between 5.7% and 6.5% must be observed. Gestational diabetes mellitus (GDM), which is not described in detail in this review, is a condition in which women without previously diagnosed diabetes exhibit high blood- glucose levels during pregnancy. Approximately 7% of all pregnancies (ranging from 1% to 14%, depending on the population studied and the diagnostic tests employed) are complicated by GDM, resulting in more than 200,000 cases annually.

Research efforts

Since the Nobel-Prize-winning 1922 discovery of insulin processing, great strides have been made to increase the quality of life in diabetic patients. In particular, the creation of human insulin through recombinant DNA technology allows the design and production of insulin analogs with different properties from those of normal insulin. Some analogs alter the three-dimensional structure of insulin so that the absorption is accelerated or delayed, or the duration of insulin action is shortened or lengthened. Currently, however, no known way exists to prevent type 1 diabetes; and, thus, a patient’s quality of life is impaired by frequent glucose monitoring and multiple insulin injections required in order to minimize his glycemic instability and its clinical consequences.¹⁷

To help the efforts toward diabetes research, the National Institute of Diabetes and Digestive and Kidney Diseases-supported Diabetes Endocrinology Research Centers (DERCs) and Diabetes Research and Training Centers (DRTCs) are funded by the federal government as part of an integrated program of diabetes, and related endocrinology and metabolism research (accessed at www.diabetescenters.org). Sixteen centers each focus on diabetes research and training. These centers are intended to improve the quality and multidisciplinary nature of research on diabetes by providing shared access to specialized technical resources and expertise. Both DERCs and DRTCs are intended to facilitate progress in research with the goal of developing new methods to prevent, treat, and — ultimately — cure diabetes and its complications.

Several clinical trials for the prevention of type 1 diabetes are currently in progress or are being planned. Some success has been demonstrated with transplants of either the whole pancreas or just the insulin-producing beta-cells of the pancreas. Several problems, however, are associated with transplanted biological or synthetic material, as the body does not recognize these foreign materials and attempts to reject them through immunological responses. These transplants require immunosuppressant regimes, which often are detrimental to the transplant recipient. In addition, the autoimmunity that caused the patient to have type 1 diabetes may result in the same fate of the newly transplanted cells.

Recently, advancement of replacing insulin-secreting cells lost to diabetes was observed through transforming spermatogonal stem cells (SSCs) — early precursors of sperm cells — into insulin-secreting cells. This proof-of-principle experiment demonstrating the possibility of extracting human SSCs from testicular tissue and changing them into insulin-secreting beta-cells normally found in the pancreas was presented at the 50^th Annual Meeting of American Society for Cell Biology. Other research has targeted specific transcription factors required for islet-cell specification. One of these transcription factors, Neurogenin3 (Ngn3), leads to long-term diabetes reversal in mice. Researchers have demonstrated that introducing Ngn3 into hepatic-progenitor cells is sufficient to induce cell-lineage switching from a liver to a beta-cell lineage.¹⁸

A recent study has shown that in a mouse model of type 1 diabetes, the adipocyte-derived hormone leptin was as effective as insulin in controlling blood sugar while eliciting fewer undesirable side effects.¹⁷ Whether or not the benefits of leptin therapy in type 1 diabetic mice can be translated to humans with type 1 diabetes will be important to determine. The amount of leptin found in people increases as their body fat increases. One effect of leptin, however, is that it acts directly on the cells of the liver and skeletal muscles where it stimulates the oxidation of fatty acids in the mitochondria. A contributing factor to glycemic instability is lability of free fatty-acid levels. When insulin falls beneath the threshold to prevent the breakdown of fats, a surge of free fatty acids can flood the targets of insulin and make them resistant to its action, thus promoting hyperglycemia.¹⁷

Another study found that leptin also inhibits bone formation.¹⁹ While the relationship of bones and diabetes was largely unknown, a link was found when researchers demonstrated that the destruction of old bone during normal skeletal regrowth (resorption) is necessary to maintain a healthy level of glucose in the blood. While resorption is a process that occurs throughout life to make way for new bone, it also acts to stimulate the release of insulin into the bloodstream and improve the uptake of glucose by cells in the entire body.²⁰ The insulin receptor is found on various cells in the body, including those cells responsible for bone formation, known as osteoblasts. This bone-specific cell favors glucose metabolism through a hormone — osteocalcin — which is active once uncarboxylated. Osteocalcin turns on the production of insulin in the pancreas and improves the ability of other cells to utilize glucose. Both of these processes are impaired in type 2 diabetes.

Summary and conclusion

Diabetes is a devastating disease that accounts for more than $132 billion in healthcare costs annually in the U.S., and these costs are predicted to rise as high as $192 billion by the year 2020¹⁶ (see recent statistics from AHRQ on page 12). For many people with diabetes, the life expectancy is shorter than that of age-matched non-diabetics. This fate is due to both the microvascular and macrovascular complications resulting from prolonged hyperglycemia. Current ADA guidelines for diagnosis include measures of plasma glucose and A1c, a glycated form of hemoglobin that has been used for many years as a marker of average glycemia. To see how A1c affects the overall number of people in the U.S. diagnosed with diabetes as a result of the test’s greater practicality will be interesting. Significant progress has been made in diabetes research through the use of stem-cell technology, molecular DNA methods, and discoveries of novel insulin-controlling systems in the body. Several federally funded diabetes-research centers across the United States are currently continuing these efforts and, ultimately, hope for a cure for diabetes and its complications.

Ross J. Molinaro, MT(ASCP), PhD, D(ABCC), F(ACB), works within the Department of Pathology and Laboratory Medicine at Emory University School of Medicine in Atlanta, GA

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