Chapter 4: Screening for Type 1 and Type 2 Diabetes
Canadian Diabetes Association 2013 Clinical Practice Guidelines
- Screening for diabetes implies testing for diabetes in individuals without symptoms who are unaware of their condition. Screening will detect individuals at increased risk for diabetes (prediabetes) or individuals with less severe states of dysglycemia who may still be at risk for type 2 diabetes.
- No distinction is made between screening and diagnostic testing for diabetes. The same tests would be used for diagnosis of both diabetes and prediabetes.
Screening for Type 1 Diabetes
- Type 1 diabetes mellitus is primarily a result of pancreatic beta cell destruction due to an immune-mediated process that is likely incited by environmental factors in genetically predisposed individuals.
- An individual’s risk of developing type 1 diabetes can be estimated by considering family history of type 1 diabetes with attention to age of onset and sex of the affected family members and profiling immunity and genetic markers.
- In the absence of evidence for interventions to prevent or delay type 1 diabetes, no recommendations for screening for type 1 diabetes can be made.
Screening for Type 2 Diabetes
- Undiagnosed type 2 diabetes may occur in >2.8% of the general adult population and the number increases to >10% in some populations.
- Routine testing for type 2 diabetes is justifiable in some but not all settings.
- While tests for hyperglycemia can identify individuals with undiagnosed type 2 diabetes, the relatively low prevalence of diabetes in the general population makes mass screening unlikely to be clinically beneficial or cost effective.
- Testing for diabetes in people with risk factors for type 2 diabetes or with diabetes-associated conditions is likely to result in more benefit than harm and will lead to overall cost savings.
- All individuals should be evaluated annually for type 2 diabetes risk on the basis of demographic and clinical criteria [Grade D, Consensus].
- Screening for diabetes using fasting blood glucose (FPG) and/or glycated hemoglobin (A1C) should be performed every 3 years in individuals ≥40 years of age or at high risk using a risk calculator [Grade D, Consensus].
- More frequent and/or earlier testing with either FPG and/or A1C or 2-hour plasma glucose (2hPG) in a 75 g oral glucose tolerance test (OGTT) should be considered in those at very high risk using a risk calculator or in people with additional risk factors for diabetes [Grade D, Consensus].
- FPG and/or A1C are the recommended screening tests.
- Testing with 2hPG in a 75 g OGTT should be undertaken in individuals with FPG 6.1–6.9 mmol/L and/or A1C 6.0%–6.4% [Grade D, Consensus].
- Testing with 2hPG in a 75 g OGTT may be undertaken in individuals with FPG 5.6–6.0 mmol/L and/or A1C 5.5%–5.9% and ≥1 diabetes risk factor(s) [Grade D, Consensus].
- People with prediabetes, especially those with impaired glucose tolerance (IGT) or an A1C of 6.0% to 6.4%, are at increased risk of developing type 2 diabetes as well as macrovascular complications, particularly in the context of the metabolic syndrome. These individuals would benefit from cardiovascular risk factor reduction strategies.
- Members of high-risk ethnic populations should be screened for prediabetes and type 2 diabetes using the recommended screening tests. However, the high prevalence of hemoglobinopathies among these populations may reduce the accuracy of A1C as a reliable screening tool. High-risk ethnic groups may also have A1C levels higher than those of Caucasians at the same level of glycemia.
Risk Prediction Tools for Type 2 Diabetes Mellitus
- Risk scoring systems must be validated for each considered population of different ethnic origin in order to adequately detect individuals at risk and eventually implement efficacious preventative strategies.
- The Canadian Diabetes Risk Assessment Questionnaire (CANRISK) is a statistically valid tool that may be suitable for diabetes risk assessment in the Canadian population.
Health Care Provider Tools
- Screening For and Diagnosing Diabetes – detailed list of risk factors and provides a risk calculator to aid in screening.
- Screening and Diagnosis - Quick Reference Guide – who to screen and how to diagnose diabetes using various screening methods.
|A1C, glycated hemoglobin; HAART, highly active antiretroviral therapy; HDL, high-density lipoprotein; HIV, human immunodeficiency virus-1; IFG, impaired fasting glucose; IGT, impaired glucose tolerance; OSA, obstructive sleep apnea.
∗ Associated with insulin resistance.
† The incidence of type 2 diabetes is at least 3 times higher in people with schizophrenia than in the general population. Using data collected in 1991, the prevalence of diabetes was assessed in >20,000 individuals diagnosed with schizophrenia. The rate of diagnosed diabetes was 9% to 14%, exceeding rates for the general population prior to the widespread use of new antipsychotic drugs.
‡ HIV and HAART increase the risk of prediabetes (IGT) and type 2 diabetes by 1.5- to 4-fold compared to the general population.
§ OSA is an independent risk factor for diabetes (hazard ratio 1.43).
For definitions of the levels of evidence cited in this chapter, please refer to the Guideline Recommendations: Levels of Evidence.
If you would like more details on this topic, including references, please visit the Canadian Diabetes Association Clinical Practice Guidelines: Chapter 4.