Diabetes is a group of diseases that result in too much sugar in the blood (high blood glucose). There are several types of diabetes, including:
- Type 1 diabetes
- Type 2 diabetes
- Gestational diabetes
- Maturity-onset diabetes of the young (MODY)
- Neonatal diabetes
- Cystic fibrosis-related diabetes
- Steroid-induced diabetes
NCBI Bookshelf. An offering from the National Library of Medicine, National Institutes of Health.
Endotext [Internet].
Carolina Solis-Herrera, MD, Curtis Triplitt, PharmD, Charles Reasner, M. D.+, Ralph A DeFronzo, M. D., and Eugenio Cersosimo, M. D. PhD.
Assistant, Clinical, and Professor of Medicine, Division of Diabetes, UTHSCSA, Mail Code 7886, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900
Last Update: February 24, 2018.
Diabetes mellitus is a chronic metabolic disorder characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. There are several types of diabetes mellitus, with the most common being type 1 diabetes, type 2 diabetes, and gestational diabetes. Other less common types include monogenic diabetes and secondary diabetes due to other medical conditions.
The classification of diabetes mellitus is important for determining the appropriate treatment and management strategies for each individual. Properly diagnosing and classifying diabetes can help healthcare providers tailor interventions to meet the specific needs of patients and improve outcomes.
It is essential for healthcare professionals to stay updated on the latest guidelines and research in diabetes classification to provide optimal care for patients with this condition.
ABSTRACT
Diabetes is a complicated metabolic disorder characterized by high blood glucose levels due to a lack of insulin or resistance to insulin. Patients are classified into type 1, type 2, or gestational diabetes, as well as other rare forms caused by various factors.
Type 1 diabetes is an autoimmune condition where the body’s immune system attacks and destroys insulin-producing cells in the pancreas. It is usually diagnosed in children and young adults. Type 2 diabetes is more common and is often associated with lifestyle factors such as obesity and lack of physical activity. Gestational diabetes occurs during pregnancy and usually resolves after giving birth.
In addition to these common types, there are also rare forms of diabetes, such as MODY (Maturity-Onset Diabetes of the Young) and LADA (Latent Autoimmune Diabetes in Adults), which have different causes and treatment approaches.
CLASSIFICATION OF DIABETES (Table 1)
Diabetes is a metabolic disorder characterized by elevated blood glucose levels caused by either a lack of insulin or insulin resistance. Individuals are categorized into type 1, type 2, or gestational diabetes, along with other less common forms influenced by different factors.
Table 1 Etiologic Classification of Diabetes Mellitus
Permanent Neonatal Diabetes (Chromosome 11p15, usually KCNJ11 encoding for KIR6.2 subunit of the beta-cell KATP channel)
TYPE 1 DIABETES MELLITUS
Type 1 diabetes occurs when the body’s immune system destroys the pancreatic beta cells. Diagnostic markers include antibodies to islet cell (ICAs), glutamic acid decarboxylase (GAD65), and insulin auto-antibodies (IAAs). Treatment involves insulin therapy.
Table 2 Staging of Type 1 DM [4b]
| Stage 1 | Stage 2 | Stage 3 | |
| Phenotypic characteristics | -Autoimmunity -Normoglycemia -Presymptomatic | -Autoimmunity -Dysglycemia -Presymptomatic | -New onset Hyperglycemia -Symptomatic |
| Diagnostic criteria | -2 or more islet autoantibodies -No impaired glucose tolerance or impaired fasting glucose | -2 or more islet autoantibodies -Dysglycemia: impaired fasting glucose and/or impaired glucose tolerance: FPG 100-125mg/dl and/or 2-hour plasma glucose 140-199mg/dl A1C 5.7-6.4% or a ≥10% increase in A1C | -Clinical symptoms -Diabetes by standard criteria |
In addition to the information provided in the table, individuals with Type 1 Diabetes Mellitus may require careful monitoring of blood sugar levels, dietary restrictions, regular exercise, and follow-up appointments with healthcare providers to manage the condition effectively. It is also important for individuals with Type 1 Diabetes to have a support system in place to help them cope with the challenges of living with a chronic illness.
TYPE 2 DIABETES MELLLITUS
Type 2 diabetes is characterized by insulin resistance and a relative lack of insulin. Over time, beta cell function deteriorates, leading to insulin deficiency. Patients are at risk of atherosclerotic cardiovascular disease due to metabolic abnormalities.
GESTATIONAL DIABETES MELLITUS (GDM)
Gestational diabetes mellitus (GDM) is a form of glucose intolerance identified during pregnancy, typically in the third trimester. After childbirth, women should undergo an oral glucose tolerance test to determine their diabetic status. GDM affects about 8-9% of pregnancies, with higher rates in high-risk groups. Early clinical detection is essential in reducing perinatal complications. Risk assessment should be conducted during the initial prenatal visit. Different groups recommend varying methods for diagnosing GDM. Various maternal and neonatal risks have been linked to maternal glycemia at 24-28 weeks. The diagnostic criteria for GDM have been updated by IADPSG using a “one-step” 75-gram OGTT, while the NIH follows a “two-step” approach. Detailed criteria for GDM diagnosis are outlined in Table 3. Screening for glucose abnormalities should occur between weeks 24-28 using a 75-gram glucose load after fasting for at least 8 hours or a 50-gram glucose load test. A fasting 100-gram glucose tolerance test is required if the initial 50-gram glucose load test shows a 1-hour plasma glucose value of ≥140mg/dl. For further information, refer to the Diabetes in Pregnancy chapter.
Table 3 Diagnosis of GDM [1]
| “One – Step” Diagnosis – 75 gram glucose tolerance test (IADPSG Consensus) | |||
|---|---|---|---|
| TIME | PLASMA GLUCOSE* | ||
| Fasting | ≥92 mg/dl | ||
| 1-hour | ≥180 mg/dl | ||
| 2-hour | ≥153 mg/dl | ||
| “Two-Step” Diagnosis – (NIH Consensus) | |||
| Step 1: Perform 50 gram glucose load test (nonfasting) | |||
| TIME | PLASMA GLUCOSE | ||
| 1-hour | ≥140 mg/dl | ||
| IF POSITIVE, STEP 2: 100 gram glucose tolerance test | |||
| Carpenter/Coustan NDDG | |||
| TIME | PLASMA GLUCOSE | TIME | PLASMA GLUCOSE |
| Fasting | ≥95 mg/dl | Fasting | ≥105 mg/dl |
| 1-hour | ≥180 mg/dl | 1-hour | ≥190 mg/dl |
| 2-hour | ≥155 mg/dl | 2-hour | ≥165 mg/dl |
| 3-hour | ≥140 mg/dl | 3-hour | ≥145 mg/dl |
| *One abnormal value is sufficient for a GDM diagnosis. The test should be done after an 8 hour fast. + Two abnormal values confirm GDM. NDDG=National Diabetes Data Group. | |||
SPECIFIC TYPES OF DIABETES
Genetic Defects
Maturity Onset Diabetes of the Young (MODY) is defined by impaired insulin secretion with minimal insulin resistance. It can manifest in neonatal or MODY-like forms, with genetic mutations affecting beta-cell function and insulin production. MODY5 is associated with renal cysts. The natural progression of MODY depends on genetic anomalies and typically presents with mild hyperglycemia from a young age, inherited in an autosomal dominant manner.
Insulin receptor mutations lead to insulin resistance. Type A insulin resistance displays a range of symptoms. Leprechaunism is a childhood disorder characterized by severe insulin resistance. Lipoatrophic diabetes is the result of defects in insulin signaling.
Several genetic syndromes linked to increased diabetes incidence have indistinct etiology in glucose homeostasis disturbances.
Diseases of the Exocrine Pancreas
Damage to the pancreas from various sources such as pancreatitis, trauma, or carcinoma can lead to the development of diabetes. Chronic pancreatitis can cause inflammation and scarring, eventually leading to diabetes. Additionally, cystic fibrosis can result in pancreatic issues, including inflammation and blockage of small ducts, which can lead to insulin deficiency. Hemochromatosis has also been linked to problems with insulin secretion and diabetes.
Hormones like growth hormone, cortisol, glucagon, and epinephrine can increase the production of glucose in the liver and contribute to insulin resistance, potentially causing or worsening diabetes. However, the development of diabetes typically requires the failure of beta cells.
Certain infections, particularly congenital rubella, have been associated with the onset of diabetes mellitus. It has been observed that around 20% of individuals infected with rubella at birth may develop type 1 diabetes later in life, often exhibiting the DR3/DR4 genotype.
Various medications commonly used can affect insulin sensitivity or impair beta cell function, leading to diabetes. Drug classes known to elevate blood sugar levels include beta-blockers, thiazide diuretics, fluoroquinolones, atypical antipsychotics, calcineurin inhibitors, protease inhibitors, nicotinic acid, and corticosteroids. Although the exact mechanisms are not fully understood, statins have also been associated with a slight increase in the risk of developing diabetes.
To explore more details on uncommon causes of diabetes, you may refer to the chapter discussing Atypical Forms of Diabetes and Diabetes Mellitus After Solid Organ Transplantation.