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Diagnosis and Screening for Diabetes


The classification of diabetes includes four clinical classes;

Type 1 diabetes results from β-cell destruction, leading to absolute insulin deficiency

Type 2 diabetes results from a progressive insulin secretory defect on the background of insulin resistance

Other specific types of diabetes due to other causes e.g., genetic defects in β-cell function, genetic defects in insulin action, diseases of the exocrine pancreas (such as cystic fibrosis) and drug- or chemical-induced diabetes (such as in the treatment of AIDS or after organ transplantation)

Gestational diabetes mellitus (GDM), diabetes diagnosed during pregnancy that is not clearly overt diabetes

Some patients cannot be clearly classified as having Type 1 or Type 2 diabetes

Clinical presentation and disease progression vary considerably in both types of diabetes

Occasionally, patients who otherwise have Type 2 diabetes may present with ketoacidosis

Similarly, patients with Type 1 diabetes may have a late onset and slow (but relentless) progression despite having features of autoimmune disease

Such difficulties in diagnosis may occur in children, adolescents and adults

The true diagnosis may become more obvious over time

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Current diagnostic criteria for the diagnosis of diabetes

A1C ≥6.5%

Fasting plasma glucose (FPG) ≥126 mg/dL (7.0 mmol/L)

Two-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an OGTT

A random plasma glucose ≥200 mg/dL (11.1 mmol/L), in patients with classic symptoms of hyperglycaemia or hyperglycaemic crisis

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In 2009, an International Expert Committee that included representatives of the American Diabetes Association (ADA), the International Diabetes Federation (IDF) and the European Association for the Study of Diabetes (EASD) recommended the use of the A1c test to diagnose diabetes, with a threshold of ≥6.5% and ADA adopted this criterion in 2010

The diagnostic test should be performed using a method certified by the National Glycohemoglobin Standardisation Program (NGSP) and standardized or traceable to the Diabetes Control and Complications Trial (DCCT) reference assay

Point-of-care A1C assays are not sufficiently accurate at this time to use for diagnostic purposes

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The established glucose criteria for the diagnosis of diabetes. FPG and two-hour plasma glucose remain valid as well

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The two-hour plasma glucose test should be performed as described by the World Health Organisation, using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water

The established glucose criteria for the diagnosis of diabetes (FPG and 2-h PG) remain valid

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As with most diagnostic tests, a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with a hyperglycaemic crisis or classic symptoms of hyperglycaemia and a random plasma glucose ≥200 mg/dL

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In 1997 and 2003, The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus recognised an intermediate group of individuals whose glucose levels, although not meeting criteria for diabetes, are nevertheless too high to be considered normal

This group was defined as having impaired fasting glucose (IFG) or impaired glucose tolerance (IGT)

IFG: Fasting plasma glucose (FPG) of 100-125 mg/dL (5.6-5.9 mmol/L)

IGT: Two-hour plasma glucose (2-h PG) on the 75-g oral glucose tolerance test (OGTT) of 140-199 mg/dL (7.8-11.0 mmol/L)

It should be noted that the World Health Organisation (WHO) and a number of other diabetes organizations define the cutoff for IFG at 110 mg/dL (6.1 mmol)

Individuals with IFG and/or IGT have been referred to as having pre-diabetes, indicating a relatively high risk for future development of diabetes

IFG and IGT should not be viewed as clinical entities in their own right but rather risk factors for diabetes as well as cardiovascular disease (CVD)

IFG and IGT are associated with obesity (especially abdominal or visceral obesity), dyslipidaemia with high triglycerides and/or low HDL cholesterol and hypertension

Individuals with an A1C of 5.7-6.4% should be informed of their increased risk for diabetes as well as CVD and counselled about effective strategies to lower their risks.

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Screening for diabetes in asymptomatic patients

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Recommendations for testing for diabetes in asymptomatic patients are summarised:

For many illnesses, there is major distinction between screening and diagnostic testing; however, for diabetes, the same tests are used for "screening" as for diagnosis

A1c, fasting plasma glucose (FPG), or two-hour oral glucose tolerance test (2-h OGTT) are appropriate to test for diabetes

The 2-h OGTT identifies people with either impaired fasting glucose (IFG) or impaired glucose tolerance (IGT); therefore, more people at increased risk for the development of diabetes and cardiovascular disease (CVD)

Type 2 diabetes has a long asymptomatic phase and significant clinical risk markers

Testing for diabetes will also detect individuals at increased future risk for diabetes; i.e., those who may have prediabetes

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This slide shows the various criteria on whom asymptomatic testing should be performed. These people are at high risk for future diabetes. In the absence of criteria (risk factors on previous slide), testing for diabetes should begin at age 45 years. If results are normal, testing should be repeated at least at 3-year intervals, with consideration of more frequent testing depending on initial results and risk status

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Detection and diagnosis of gestational diabetes mellitus

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Recommendations for the detection and diagnosis of gestational diabetes mellitus (GDM) are summarised:

As the ongoing epidemic of obesity and diabetes has led to more Type 2 diabetes in women of childbearing age, the number of pregnant women with undiagnosed Type 2 diabetes has increased

Because of this, it is reasonable to screen women with risk factors for Type 2 diabetes for diabetes at their initial pre-natal visit, using standard diagnostic criteria; women with diabetes found at this visit should receive a diagnosis of overt, not gestational, diabetes.

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Recommendations for the detection and diagnosis of gestational diabetes mellitus (GDM) are summarised:

Women with a history of GDM have a greatly increased subsequent risk for diabetes; therefore, they should be screened for diabetes 6-12 weeks postpartum, using non-pregnant oral glucose tolerance test (OGTT) criteria and should be followed for the development of diabetes or prediabetes. Women with a history of GDM should have lifelong screening for the development of diabetes or prediabetes at least every three years

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Prevention/delay of Type 2 diabetes

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Recommendations for the prevention/delay of Type 2 diabetes are summarised:

Individuals at high risk for developing diabetes (i.e., those with impaired fasting glucose [IFG], impaired glucose tolerance [IGT] or both) can be given interventions that significantly decrease rate of onset of diabetes

Based on results of clinical trials and known risks of progression of prediabetes to diabetes, person with an A1c of 5.7%-6.4%, IGT or IFG should be counselled on lifestyle changes: 7% weight loss and moderate physical activity of at least 150 minutes/week

Regarding the more controversial issue of drug therapy for diabetes prevention, a consensus panel believed that Metformin should be the only drug considered

Metformin may be recommended for very high-risk individuals (those with risk factors for diabetes and/or those with more severe or progressive hyperglycemia)

Of note, in the Diabetes Prevention Program (DPP), Metformin was most effective compared to lifestyle in individuals with BMI ≥35 kg/m2 and was not significantly better than placebo in those over age 60 years

For other drugs, issues of cost, side effects and lack of persistence of effect in some studies led the panel to not recommend use for diabetes prevention

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