Type 1 Diabetes Mellitus

Updated: Sep 30, 2016
  • Author: Romesh Khardori, MD, PhD, FACP; Chief Editor: George T Griffing, MD  more...
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Practice Essentials

Type 1 diabetes is a chronic illness characterized by the body’s inability to produce insulin due to the autoimmune destruction of the beta cells in the pancreas. Onset most often occurs in childhood, but the disease can also develop in adults in their late 30s and early 40s. [1]

See Clinical Findings in Diabetes Mellitus, a Critical Images slideshow, to help identify various cutaneous, ophthalmologic, vascular, and neurologic manifestations of DM.

Signs and symptoms

The classic symptoms of type 1 diabetes are as follows:

  • Polyuria
  • Polydipsia
  • Polyphagia
  • Unexplained weight loss

Other symptoms may include fatigue, nausea, and blurred vision.

The onset of symptomatic disease may be sudden. It is not unusual for patients with type 1 diabetes to present with diabetic ketoacidosis (DKA).

See Clinical Presentation for more detail.


Diagnostic criteria by the American Diabetes Association (ADA) include the following [2] :

  • A fasting plasma glucose (FPG) level ≥126 mg/dL (7.0 mmol/L), or
  • A 2-hour plasma glucose level ≥200 mg/dL (11.1 mmol/L) during a 75-g oral glucose tolerance test (OGTT), or
  • A random plasma glucose ≥200 mg/dL (11.1 mmol/L) in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis

Lab studies

A fingerstick glucose test is appropriate for virtually all patients with diabetes. All fingerstick capillary glucose levels must be confirmed in serum or plasma to make the diagnosis. All other laboratory studies should be selected or omitted on the basis of the individual clinical situation.

An international expert committee appointed by the ADA, the European Association for the Study of Diabetes, and the International Diabetes Association recommended the HbA1c assay for diagnosing type 1 diabetes only when the condition is suspected but the classic symptoms are absent. [3]


Screening for type 1 diabetes in asymptomatic low-risk individuals is not recommended. [2] However, in patients at high risk (eg, those who have first-degree relatives with type 1 diabetes), it may be appropriate to perform annual screening for anti-islet antibodies before the age of 10 years, along with 1 additional screening during adolescence. [4]

See Workup for more detail.


Glycemic control

The ADA recommends using patient age as one consideration in the establishment of glycemic goals, with different targets for preprandial, bedtime/overnight, and hemoglobin A1c (HbA1c) levels in patients aged 0-6, 6-12, and 13-19 years. [5] Benefits of tight glycemic control include not only continued reductions in the rates of microvascular complications but also significant differences in cardiovascular events and overall mortality.


Optimal diabetic control requires frequent self-monitoring of blood glucose levels, which allows rational adjustments in insulin doses. All patients with type 1 diabetes should learn how to self-monitor and record their blood glucose levels with home analyzers and adjust their insulin doses accordingly.

Real-time continuous monitoring of glucose—using continuous glucose monitors (CGMs)—can help patients improve glycemic control. [6, 7] CGMs contain subcutaneous sensors that measure interstitial glucose levels every 1-5 minutes, providing alarms when glucose levels are too high or too low or are rapidly rising or falling.

Insulin therapy

Patients with type 1 diabetes require lifelong insulin therapy. Most require 2 or more injections of insulin daily, with doses adjusted on the basis of self-monitoring of blood glucose levels. Insulin replacement is accomplished by giving a basal insulin and a preprandial (premeal) insulin. The basal insulin is either long-acting (glargine or detemir) or intermediate-acting (NPH). The preprandial insulin is either rapid-acting (lispro, aspart, insulin inhaled, or glulisine) or short-acting (regular).

Common insulin regimens include the following:

  • Split or mixed: NPH with rapid-acting (eg, lispro, aspart, or glulisine) or regular insulin before breakfast and supper
  • Split or mixed variant: NPH with rapid-acting or regular insulin before breakfast, rapid-acting or regular insulin before supper, and NPH before bedtime (the idea is to reduce fasting hypoglycemia by giving the NPH later in the evening)
  • Multiple daily injections (MDI): A long-acting insulin (eg, glargine or detemir) once a day in the morning or evening (or twice a day in about 20% of patients) and a rapid-acting insulin before meals or snacks (with the dose adjusted according to the carbohydrate intake and the blood glucose level)
  • Continuous subcutaneous insulin infusion (CSII): Rapid-acting insulin infused continuously 24 hours a day through an insulin pump at 1 or more basal rates, with additional boluses given before each meal and correction doses administered if blood glucose levels exceed target levels

Diet and activity

All patients on insulin should have a comprehensive diet plan, created with the help of a professional dietitian, that includes the following:

  • A daily caloric intake prescription
  • Recommendations for amounts of dietary carbohydrate, fat, and protein
  • Instructions on how to divide calories between meals and snacks

Exercise is also an important aspect of diabetes management. Patients should be encouraged to exercise regularly.

See Treatment and Medication for more detail.



Type 1 diabetes mellitus (DM) is a multisystem disease with both biochemical and anatomic/structural consequences. It is a chronic disease of carbohydrate, fat, and protein metabolism caused by the lack of insulin, which results from the marked and progressive inability of the pancreas to secrete insulin because of autoimmune destruction of the beta cells. [1] (See Pathophysiology.) (See also Glucose Intolerance.)

Type 1 DM can occur at any age. It is most common in juveniles but can also develop in adults, especially in those in their late 30s and early 40s. (See Epidemiology.)

Unlike people with type 2 DM, those with type 1 DM usually are not obese and usually present initially with diabetic ketoacidosis (DKA). The distinguishing characteristic of a patient with type 1 DM is that if his or her insulin is withdrawn, ketosis and eventually ketoacidosis develop. Therefore, these patients are dependent on exogenous insulin. (See Presentation.)

Treatment of type 1 DM requires lifelong insulin therapy. A multidisciplinary approach by the physician, nurse, and dietitian, with regular specialist consultation, is needed to control glycemia, as well as to limit the development of its devastating complications and manage such complications when they do occur. (See Treatmentand Medication.)

Despite the differences between type 1 and type 2 DM, the costs of the 2 conditions are often combined. In a study that focused on type 1 alone, Tao et al estimated that in the United States, type 1 DM is responsible for $14.4 billion in medical costs and lost income each year. [8]



Type 1 DM is the culmination of lymphocytic infiltration and destruction of insulin-secreting beta cells of the islets of Langerhans in the pancreas. As beta-cell mass declines, insulin secretion decreases until the available insulin no longer is adequate to maintain normal blood glucose levels. After 80-90% of the beta cells are destroyed, hyperglycemia develops and diabetes may be diagnosed. Patients need exogenous insulin to reverse this catabolic condition, prevent ketosis, decrease hyperglucagonemia, and normalize lipid and protein metabolism.

Currently, autoimmunity is considered the major factor in the pathophysiology of type 1 DM. In a genetically susceptible individual, viral infection may stimulate the production of antibodies against a viral protein that trigger an autoimmune response against antigenically similar beta cell molecules.

Approximately 85% of type 1 DM patients have circulating islet cell antibodies, and the majority also have detectable anti-insulin antibodies before receiving insulin therapy. The most commonly found islet cell antibodies are those directed against glutamic acid decarboxylase (GAD), an enzyme found within pancreatic beta cells.

The prevalence of type 1 DM is increased in patients with other autoimmune diseases, such as Graves disease, Hashimoto thyroiditis, and Addison disease. Pilia et al found a higher prevalence of islet cell antibodies (IA2) and anti-GAD antibodies in patients with autoimmune thyroiditis. [9]

A study by Philippe et al used computed tomography (CT) scans, glucagon stimulation test results, and fecal elastase-1 measurements to confirm reduced pancreatic volume in individuals with DM. [10] This finding, which was equally present in both type 1 and type 2 DM, may also explain the associated exocrine dysfunction that occurs in DM.

Polymorphisms of the class II human leukocyte antigen (HLA) genes that encode DR and DQ are the major genetic determinants of type 1 DM. Approximately 95% of patients with type 1 DM have either HLA-DR3 or HLA-DR4. Heterozygotes for those haplotypes are at significantly greater risk for DM than homozygotes. HLA-DQs are also considered specific markers of type 1 DM susceptibility. In contrast, some haplotypes (eg, HLA-DR2) confer strong protection against type 1 DM. [11]

Sensory and autonomic neuropathy

Sensory and autonomic neuropathy in people with diabetes are caused by axonal degeneration and segmental demyelination. Many factors are involved, including the accumulation of sorbitol in peripheral sensory nerves from sustained hyperglycemia. Motor neuropathy and cranial mononeuropathy result from vascular disease in blood vessels supplying nerves.


Using nailfold video capillaroscopy, Barchetta et al detected a high prevalence of capillary changes in patients with diabetes, particularly those with retinal damage. This reflects a generalized microvessel involvement in both type 1 and type 2 DM. [12]

Microvascular disease causes multiple pathologic complications in people with diabetes. Hyaline arteriosclerosis, a characteristic pattern of wall thickening of small arterioles and capillaries, is widespread and is responsible for ischemic changes in the kidney, retina, brain, and peripheral nerves.

Atherosclerosis of the main renal arteries and their intrarenal branches causes chronic nephron ischemia. It is a significant component of multiple renal lesions in diabetes.

Vitamin D deficiency is an important independent predictor of development of coronary artery calcification in individuals with type 1 DM. [13] Joergensen et al determined that vitamin D deficiency in type 1 diabetes may predict all causes of mortality but not development of microvascular complications. [14]


In the kidneys, the characteristic wall thickening of small arterioles and capillaries leads to diabetic nephropathy, which is characterized by proteinuria, glomerular hyalinization (Kimmelstiel-Wilson), and chronic renal failure. Exacerbated expression of cytokines such as tumor growth factor beta 1 is part of the pathophysiology of glomerulosclerosis, which begins early in the course of diabetic nephropathy.

Genetic factors influence the development of diabetic nephropathy. Single-nucleotide polymorphisms affecting the factors involved in its pathogenesis appear to influence the risk for diabetic nephropathy in different people with type 1 DM. [15]

Double diabetes

In areas where rates of type 2 DM and obesity are high, individuals with type 1 DM may share genetic and environmental factors that lead to their exhibiting type 2 features such as reduced insulin sensitivity. This condition is termed double diabetes.

In a study that included 207 patients with type 1 DM, Epstein et al used the estimated glucose disposal rate (eGDR) to assess insulin resistance and found that mean eGDR was significantly lower (and, thus, insulin resistance was higher) in black patients (5.66 mg/kg/min) than in either Hispanic patients (6.70 mg/kg/min) or white patients (7.20 mg/kg/min). In addition, low eGDR was associated with an increased risk of vascular complications of diabetes (eg, cardiovascular disease, diabetic retinopathy, or severe chronic kidney disease). [16, 17]



Type 1A DM results from autoimmune destruction of the beta cells of the pancreas and involves both genetic predisposition and an environmental component.

Genetic factors

Although the genetic aspect of type 1 DM is complex, with multiple genes involved, there is a high sibling relative risk. [18] Whereas dizygotic twins have a 5-6% concordance rate for type 1 DM, [19] monozygotic twins will share the diagnosis more than 50% of the time by the age of 40 years. [20]

For the child of a parent with type 1 DM, the risk varies according to whether the mother or the father has diabetes. Children whose mother has type 1 DM have a 2-3% risk of developing the disease, whereas those whose father has the disease have a 5-6% risk. When both parents are diabetic, the risk rises to almost 30%. In addition, the risk for children of parents with type 1 DM is slightly higher if onset of the disease occurred before age 11 years and slightly lower if the onset occurred after the parent’s 11th birthday.

The genetic contribution to type 1 DM is also reflected in the significant variance in the frequency of the disease among different ethnic populations. Type 1 DM is most prevalent in European populations, with people from northern Europe more often affected than those from Mediterranean regions. [21] The disease is least prevalent in East Asians. [22]

Genome-wide association studies have identified several loci that are associated with type 1 DM, but few causal relations have been established. The genomic region most strongly associated with other autoimmune diseases, the major histocompatibility complex (MHC), is the location of several susceptibility loci for type 1 DM—in particular, class II HLA DR and DQ haplotypes. [23, 24, 25]

A hierarchy of DR-DQ haplotypes associated with increased risk for type 1 DM has been established. The most susceptible haplotypes are as follows [26] :

  • DRB1*0301 - DQA1*0501 - DQB1*0201 (odds ratio [OR] 3.64)
  • DRB1*0405 - DQA1*0301 - DQB1*0302 (OR 11.37)
  • DRB1*0401 - DQA1*0301 - DQB*0302 (OR 8.39)
  • DRB1*0402 - DQA1*0301 - DQB1*0302 (OR 3.63)
  • DRB1*0404 - DQA1*0301 - DQB1*0302 (OR 1.59)
  • DRB1*0801 - DQB1*0401 - DQB1*0402 (OR 1.25)

Other haplotypes appear to offer protection against type 1 DM. These include the following [26] :

  • DRB1*1501 - DQA1*0102 - DQB1*0602 (OR 0.03)
  • DRB1*1401 - DQA1*0101 - DQB1*0503 (OR 0.02)
  • DRB1*0701 - DQA1*0201 - DQB1*0303 (OR 0.02)

From 90% to 95% of young children with type 1 DM carry HLA-DR3 DQB1*0201, HLA-DR4 DQB1*0302, or both. Carriage of both haplotypes (ie, DR3/4 heterozygotes) confers the highest susceptibility.

These high-risk haplotypes are found primarily in people of European descent; other ethnic groups are less well studied. In African Americans, the DRB1*07:01 - DQA1*03:01 -DQB1*02:01g haplotype is associated with increased risk (OR 3.96), whereas the DRB1*07:01-DQA1*02:01 - DQB1*02:01g haplotype appears to be protective (OR 0.34). [27]

The insulin gene (INS), which encodes for the pre-proinsulin peptide, is adjacent to a variable number of tandem repeats (VNTR) polymorphism at chromosome 11p15.5. [28] Different VNTR alleles may promote either resistance or susceptibility to type 1 DM through their effect on INS transcription in the thymus; for example, protective VNTRs are associated with higher INS expression, which may promote deletion of insulin-specific T cells. [29]

Other genes that have been reported to be involved in the mechanism of type 1 DM include CTLA4 (important in T-cell activation), PTPN22 (produces LYP, a negative regulator of T-cell kinase signaling), and IL2RA (encodes for CD25 which is involved with regulating T-cell function). UBASH3A (also known as STS2), may be involved in the increased risk not only of type 1 DM but also of other autoimmune disease and Down syndrome; it is located on locus chromosome 21q22.3. [30]

In addition, genome-wide association studies have implicated numerous other genes, including the following [31] :

  • SH2B3
  • ERBB3
  • CLEC16A
  • IL18RAP
  • PTPN2
  • CCR5

Environmental factors

Extragenetic factors also may contribute. Potential triggers for immunologically mediated destruction of the beta cells include viruses (eg, enterovirus, [32] mumps, rubella, and coxsackievirus B4), toxic chemicals, exposure to cow’s milk in infancy, [33] and cytotoxins.

Combinations of factors may be involved. Lempainen et al found that signs of an enterovirus infection by 12 months of age were associated with the appearance of type 1 DM–related autoimmunity among children who were exposed to cow's milk before 3 months of age. These results suggest an interaction between the 2 factors and provide a possible explanation for the contradictory findings obtained in studies that examined these factors in isolation. [34]

One meta-analysis found a weak but significant linear increase in the risk of childhood type 1 DM with increasing maternal age. [35] However, little evidence supports any substantial increase in childhood type 1 DM risk after pregnancy complicated by preeclampsia. [36]

A study by Simpson et al found that neither vitamin D intake nor 25-hydroxyvitamin D levels throughout childhood were associated with islet autoimmunity or progression to type 1 DM. [37] This study was based in Denver, Colorado, and has been following children at increased risk of diabetes since 1993.

Early upper respiratory infection may also be a risk factor for type 1 diabetes. In an analysis of data on 148 children considered genetically at risk for diabetes, upper respiratory infections in the first year of life were associated with an increased risk for type 1 diabetes . [38, 39] All children in the study who developed islet autoimmunity had at least 2 upper respiratory infections in the first year of life and at least 1 infection within 6 months before islet autoantibody seroconversion.

Children with respiratory infections in the first 6 months of life had the greatest increased hazard ratio (HR) for islet autoantibody seroconversion (HR = 2.27), and the risk was also increased in those with respiratory infections at ages 6 to almost 12 months (HR = 1.32). [38, 39] The rate of islet autoantibody seroconversion was highest among children with more than 5 respiratory infections in the first year of year of life. Respiratory infections in the second year of life were not related to increased risk. [38, 39]



United States statistics

A 2011 report from the US Centers for Disease Control and Prevention (CDC) estimated that approximately 1 million Americans have type 1 DM. [40] The CDC estimated that each year from 2002 to 2005, type 1 DM was newly diagnosed in 15,600 young people. Among children younger than 10 years, the annual rate of new cases was 19.7 per 100,000 population; among those 10 years or older, the rate was 18.6 per 100,000 population. [40]

Type 1 DM is the most common metabolic disease of childhood. About 1 in every 400-600 children and adolescents has type 1 DM. In adults, type 1 DM constitutes approximately 5% of all diagnosed cases of diabetes. [40]

International statistics

Internationally, rates of type 1 DM are increasing. In Europe, the Middle East, and Australia, rates of type 1 DM are increasing by 2-5% per year. [41] The prevalence of type 1 DM is highest in Scandinavia (ie, approximately 20% of the total number of people with DM) and lowest in China and Japan (ie, fewer than 1% of all people with diabetes). Some of these differences may relate to definitional issues and the completeness of reporting.

Age-related demographics

Previously referred to as juvenile-onset diabetes, type 1 DM is typically diagnosed in childhood, adolescence, or early adulthood. Although the onset of type 1 DM often occurs early in life, 50% of patients with new-onset type 1 DM are older than 20 years of age.

Type 1 DM usually starts in children aged 4 years or older, appearing fairly abruptly, with the peak incidence of onset at age 11-13 years (ie, in early adolescence and puberty). There is also a relatively high incidence in people in their late 30s and early 40s, in whom the disease tends to present less aggressively (ie, with early hyperglycemia without ketoacidosis and gradual onset of ketosis). This slower-onset adult form of type 1 DM is referred to as latent autoimmune diabetes of the adult (LADA). [40]

The risk of development of antibodies (anti-islet) in relatives of patients with type 1 DM decreases with increasing age. This finding supports annual screening for antibodies in relatives younger than 10 years and 1 additional screening during adolescence. [4]

Sex- and race-related demographics

Type 1 DM is more common in males than in females. In populations of European origin, the male-to-female ratio is greater than 1.5:1.

Type 1 DM is most common among non-Hispanic whites, followed by African Americans and Hispanic Americans. It is comparatively uncommon among Asians.



Type 1 DM is associated with a high morbidity and premature mortality. More than 60% of patients with type 1 DM do not develop serious complications over the long term, but many of the rest experience blindness, end-stage renal disease (ESRD), and, in some cases, early death. The risk of ESRD and proliferative retinopathy is twice as high in men as in women when the onset of diabetes occurred before age 15 years. [42]

Patients with type 1 DM who survive the period 10-20 years after disease onset without fulminant complications have a high probability of maintaining reasonably good health. Other factors affecting long-term outcomes are the patient’s education, awareness, motivation, and intelligence level. The 2012 American Diabetes Association (ADA) standard of care emphasizes the importance of long-term, coordinated care management for improved outcomes and suggests structural changes to existing systems of long-term care delivery. [5]

The morbidity and mortality associated with diabetes are related to the short- and long-term complications. Such complications include the following:

  • Hypoglycemia from management errors
  • Increased risk of infections
  • Microvascular complications (eg, retinopathy and nephropathy)
  • Neuropathic complications
  • Macrovascular disease

These complications result in increased risk for ischemic heart disease, cerebral vascular disease, peripheral vascular disease with gangrene of lower limbs, chronic renal disease, reduced visual acuity and blindness, and autonomic and peripheral neuropathy. Diabetes is the major cause of blindness in adults aged 20-74 years, as well as the leading cause of nontraumatic lower-extremity amputation and ESRD.

In both diabetic and non-diabetic patients, coronary vasodilator dysfunction is a strong independent predictor of cardiac mortality. In diabetic patients without coronary artery disease, those with impaired coronary flow reserve have event rates similar to those with prior coronary artery disease, while patients with preserved coronary flow reserve have event rates similar to non-diabetic patients. [43]

Type 1 diabetic patients also have a high prevalence of small-fiber neuropathy. [44, 45] In a prospective study of 27 patients who had type 1 diabetes with a mean disease duration of 40 years, almost 60% of the subjects showed signs or symptoms of neuropathy, including sensory neuropathy symptoms (9 patients), pain (3 patients), and carpal-tunnel symptoms (5 patients). [44, 45] Of the 27 patients, 22 were diagnosed with small-fiber dysfunction by means of quantitative sensory testing.

Abnormal results on intraepidermal nerve-fiber density measurement (IENFD) were seen in 19 patients. [45] IENFD was negatively correlated with HbA1c, but this relation was no longer significant after adjustment for age, body mass index, and height. N-ε-(carboxymethyl) lysine (CML), which is linked to painful diabetic neuropathy, remained independently associated with IENFD even after adjustment for these variables. Large-fiber neuropathy was also common, being found in 16 patients.

Although ESRD is one of the most severe complications of type 1 DM, its incidence is relatively low: 2.2% at 20 years after diagnosis and 7.8% at 30 years after diagnosis. [46] A greater risk is that mild diabetic nephropathy in type 1 diabetic persons appears to be associated with an increased likelihood of cardiovascular disease. [47] Moreover, the long-term risk of an impaired glomerular filtration rate (GFR) is lower in persons treated with intense insulin therapy early in the course of disease than in those given conventional therapy. [48]

Although mortality from early-onset type 1 DM (onset age, 0-14 y) has declined, the same may not be true for late-onset type 1 DM (onset age, 15-29 y). One study suggest that women tend to fare worse in both cohorts and that alcohol and drug use account for more than one third of deaths. [49]

Control of blood glucose, hemoglobin A1c (HbA1c), lipids, blood pressure, and weight significantly affects prognosis. Excess weight gain with intensified diabetes treatment is associated with hypertension, insulin resistance, dyslipidemia and extetnsive atherosclerotic cardiovascular disease. [50]

Patients with diabetes face a lifelong challenge to achieve and maintain blood glucose levels as close to the normal range as possible. With appropriate glycemic control, the risk of both microvascular and neuropathic complications is decreased markedly. In addition, aggressive treatment of hypertension and hyperlipidemia decreases the risk of macrovascular complications.

The benefits of glycemic control and control of comorbidities must be weighed against the risk of hypoglycemia and the short-term costs of providing high-quality preventive care. However, studies have shown cost savings due to a reduction in acute diabetes-related complications within 1-3 years of starting effective preventive care.


Patient Education

Education is a vital aspect of diabetes management. Patients with new-onset type 1 DM require extensive education if they are to manage their disease safely and effectively and to minimize long-term complications. Such education is best coordinated by the patient’s long-term care providers.

At every encounter, the clinician should educate the patient—and, in the case of children, the parents—about the disease process, management, goals, and long-term complications. In particular, clinicians should do the following:

  • Make patients aware of the signs and symptoms of hypoglycemia and knowledgeable about ways to manage it
  • Help patients understand and acknowledge the course of diabetes (eg, by teaching patients that they have a chronic condition that requires lifestyle modification and that they are likely to have chronic complications if they do not take control of their disease)
  • Reassure patients about the prognosis in properly managed type 1 DM

ADA guidelines urge that attention be paid to older adolescent patients who may be leaving their home and their current health care providers. At the transition between pediatric and adult health care, older teens can become detached from the health care system, putting their medical care and their glycemic control at risk. [5] The guidelines identify the National Diabetes Education Program (NDEP) as a source of materials that can help smooth the transition to adult health care.

Education about an appropriate treatment plan and encouragement to follow the plan are especially important in patients with diabetes. Physicians must ensure that the care for each patient with diabetes includes all necessary laboratory tests, examinations (eg, foot and neurologic examinations), and referrals to specialists (eg, an ophthalmologist or podiatrist).

A dietitian should provide specific diet control education to the patient and family. A nurse should educate the patient about self–insulin injection and performing fingerstick tests for blood glucose level monitoring.

For patient education information, see the Diabetes Center, as well as Diabetes.