Classification & Screening of Diabetes Mellitus

Diabetes Mellitus

Classification and Screening of Diabetes Mellitus - Classification of Diabetes

Diabetes is a metabolic disorder characterized by resistance to the action of insulin, insufficient insulin secretion, or both. The clinical manifestation of these disorders is hyperglycemia. The vast majority of diabetic patients are classified into one of two broad categories: type 1 diabetes caused by an absolute deficiency of insulin, or type 2 diabetes defined by the presence of insulin resistance with an inadequate compensatory increase in insulin secretion. Women who develop diabetes because of the stress of pregnancy are classified as having gestational diabetes. Finally, uncommon types of diabetes caused by infections, drugs, endocrinopathies, pancreatic destruction, and known genetic defects are classified separately (Table).

Etiologic Classification of Diabetes Mellitus

Type 1 Diabetes

This form of diabetes results from autoimmune destruction of the β cells of the pancreas. Markers of immune destruction of the β cell are present at the time of diagnosis in 90% of individuals and include islet cell antibodies, antibodies to glutamic acid decarboxylase, and antibodies to insulin. Although this form of diabetes usually occurs in children and adolescents, it can occur at any age. Younger individuals typically have a rapid rate of β-cell destruction and present with ketoacidosis, whereas adults often maintain sufficient insulin secretion to prevent ketoacidosis for many years, which is often referred to as LADA.

Type 2 Diabetes

This form of diabetes is characterized by insulin resistance and a relative lack of insulin secretion, with progressively lower insulin secretion over time. Most individuals with type 2 diabetes exhibit abdominal obesity, which itself causes insulin resistance. In addition, hypertension, dyslipidemia (high triglyceride levels and low HDL-cholesterol levels), and elevated plasminogen activator inhibitor type 1 (PAI-1) levels are often present in these individuals. This clustering of abnormalities is referred to as the insulin resistance syndrome or the metabolic syndrome. Because of these abnormalities, patients with type 2 diabetes are at increased risk of developing macrovascular complications. Type 2 diabetes has a strong genetic predisposition and is more common in all ethnic groups other than those of European ancestry. At this point the genetic cause of most cases of type 2 diabetes is not well defined.

Gestational Diabetes Mellitus

GDM is defined as glucose intolerance that is first recognized during pregnancy. Gestational diabetes complicates approximately 7% of all pregnancies. Clinical detection is important, as therapy will reduce perinatal morbidity and mortality. 

Other Specific Types of Diabetes

Genetic Defects MODY is characterized by impaired insulin secretion with minimal or no insulin resistance. Patients typically exhibit mild hyperglycemia at an early age. The disease is inherited in an autosomal dominant pattern with at least six different loci identified to date. Genetic inability to convert proinsulin to insulin results in mild hyperglycemia and is inherited in an autosomal dominant pattern. Similarly, the production of mutant insulin molecules has been identified in a few families and results in mild glucose intolerance.

Several genetic mutations have been described in the insulin receptor and are associated with insulin resistance. Type A insulin resistance refers to the clinical syndrome of acanthosis nigricans, virilization in women, polycystic ovaries, and hyperinsulinemia. In contrast, type B insulin resistance is caused by autoantibodies to the insulin receptor. Leprechaunism is a pediatric syndrome with specific facial features and severe insulin resistance because of a defect in the insulin receptor gene. Lipoatrophic diabetes probably results from postreceptor defects in insulin signaling.

Screening

Type 1 Diabetes Mellitus

There is still a low prevalence of type 1 DM in the general population and because of the acuteness of symptoms, screening for type 1 DM is not recommended.

Type 2 Diabetes Mellitus

Based on expert opinion, and not uniformly accepted by all guidance organizations, the American Diabetes Association (ADA) recommends screening for type 2 DM every 3 years in all adults beginning at age 45 years. Testing should be considered at an earlier age and more frequently in individuals with risk factors. The recommended screening test is the fasting plasma glucose (FPG). An oral glucose tolerance test (OGTT) (more costly, less convenient, less reproducible) can be performed alternatively or in addition to FPG when a high index of suspicion for the disease is present.

Children and Adolescents

Despite a lack of clinical evidence to support widespread testing of children for type 2 DM, it is clear that more children and adolescents are developing type 2 DM. The ADA, by expert opinion, recommends that overweight (defined as BMI >85th percentile for age and sex, weight for height >85th percentile, or weight >120% of ideal [50th percentile] for height) youths with at least two of the following risk factors: a family history of type 2 diabetes in first- and second-degree relatives; Native Americans, African Americans, Hispanic Americans, and Asians/South Pacific Islanders; and those with signs of insulin resistance or conditions associated with insulin resistance (acanthosis nigricans, hypertension, dyslipidemia, or polycystic ovary syndrome) be screened. Testing should be done every 2 years starting at 10 years of age or at the onset of puberty if it occurs at a younger age.

Gestational Diabetes

Risk assessment for GDM should occur at the first prenatal visit. Women at high risk (positive family history, history of GDM, marked obesity, or member of a high-risk ethnic group) should be screened as soon as feasible. If the initial screening is negative, they should undergo retesting at 24 to 28 weeks of gestation, as should all other pregnant women with the possible exception of low-risk primigravidas. Evaluation for GDM can be done in one of two ways. The one-step approach involves a 3-hour, 100 gram-OGTT and can be cost-effective in high-risk patient populations. The two-step approach uses a screening test to measure plasma or serum glucose concentration 1 hour after a 50 gram oral glucose load (glucose challenge test), followed by a diagnostic 3-hour OGTT on the subset of women exceeding a glucose threshold of either ≥140 mg/dL (80% sensitive) or ≥130 mg/dL (90% sensitive). The diagnosis of GDM is based on a 75-gram (not as well validated) or 100-gram OGTT. Criteria for diagnosis of GDM based on the OGTT are summarized in Table bellow

Diagnosis of Gestational Diabetes Mellitus with a
100-g or 75-g Glucose Load

Salam

by Umaee

Classification and Screening of Diabetes Mellitus

Source: Pharmacotherapy 7th

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