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August 17, 2019 Screening for and diagnosing diabetes

Risk factors for type 2 diabetes

  • Age ≥40 years
  • First-degree relative with type 2 diabetes
  • Member of high-risk population (e.g., African, Arab, Asian, Hispanic, Indigenous or South Asian descent, low socioeconomic status)
  • History of prediabetes (lGT, lFG or A1C 6.0–6.4%)*
  • History of GDM
  • History of delivery of a macrosomic infant
  • Presence of end organ damage associated with diabetes:
    • Microvascular (retinopathy, neuropathy, nephropathy)
    • CV (coronary, cerebrovascular, peripheral)
  • Presence of vascular risk factors:
    • HDL-C <1.0 mmol/L in males, <1.3 mmol/L in females*
    • TG ≥1.7 mmol/L*
    • Hypertension*
    • Overweight*
    • Abdominal obesity*
    • Smoking
  • Presence of associated diseases:
    • History of pancreatitis
    • Polycystic ovary syndrome*
    • Acanthosis nigricans*
    • Hyperuricemia/gout
    • Non-alcoholic steatohepatitis
    • Psychiatric disorders (bipolar disorder, depression, schizophrenia†)
    • HlV infection‡
    • Obstructive sleep apnea§
    • Cystic fibrosis
  • Use of drugs associated with diabetes:
    • Glucocorticoids
    • Atypical antipsychotics
    • Statins
    • Highly active antiretroviral therapy‡
    • Anti-rejection drugs
    • Other (see Appendix 1)
  • Other secondary causes (see Appendix 1)

AIC, glycated hemoglobin; CV, cardiovascular; GDM, gestational diabetes; HDL-C, high density lipoprotein cholesterol; HIV, human immunodeficiency virus-1; IFG, impaired fasting glucose; IGT, impaired glucose tolerance.

When to screen for type 2 diabetes

  • Screen every 3 years in individuals ≥40 years of age
  • Screen every 3 years in individuals at high risk according to a risk calculator
  • Screen earlier and/or more frequently (every 6 to 12 months) in people with additional risk factors for diabetes (see below)
  • Screen earlier and/or more frequently in people at very high risk according to a risk calculator

Conditions that lead to misleading A1C include: hemoglobinopathies, hemolytic anemia, iron deficiency, severe renal or liver disease. Link to Table 1, Monitoring for Glycemic Control.

  1. Validated Assay: A1C must be measured using a validated assay standardized to the National Glycohemoglobin Standardization Program-Diabetes Control and Complications Trial reference.
  2. Ethnicity: Studies indicate that African Americans, American Indians, Hispanics and Asians have A1C values that are up to 0.4% higher than those of Caucasian patients at similar levels of glycemia (17,18). Research is required to determine if A1C levels differ in African Canadians or Canadian First Nations.
  3. Age: A1C values are affected by age, rising by up to 0.1% per decade of life (20,21). More studies may help to determine if age- or ethnic-specific adjusted A1C thresholds are required for diabetes diagnosis.
  4. Special Populations: A1C is not recommended for diagnostic purposes in children, adolescents, pregnant women or those with suspected type 1 diabetes.

See Individualizing Your Patient’s A1C target, Chapter 9: Monitoring Glycemic Control, Table 1

Click here to view the Canadian Diabetes Risk Questionnaire (CANRISK) (printable and downloadable version)

Click here to view the Canadian Diabetes Risk Questionnaire (CANRISK) interactive online questionnaire

Screening algorithm

Chapter 4: Figure 1. Screening and diagnosis algorithm for type 2 diabetes.

Chapter 3: Table 5
Diagnosis of prediabetes
2hPG, 2-hour plasma glucose; AlC, glycated hemoglobin; FPG, fasting plasma glucose; IFG, impaired fasting glucose; IGT, impaired glucose tolerance; OGTT, oral glucose tolerance test.
Test Result Prediabetes category
FPG (mmol/L) 6.1–6.9 IFG
2hPG in a 75 g OGTT (mmol/L) 7.8–11.0 IGT
A1C (%) 6.0–6.4 Prediabetes

Advantages and disadvantages of diagnostic tests for diabetes

Parameter Advantages Disadvantages
2hPG, 2-hour plasma glucose; A1C, glycated hemoglobin; CVD, cardiovascular disease; FPG, fasting plasma glucose; OGTT, ral glucose tolerance test.
FPG
  • Established standard
  • Fast and easy
  • Single sample
  • Predicts microvascular complications
  • Sample not stable
  • High day-to-day variability
  • Inconvenient (fasting)
  • Reflects glucose homeostasis at a single point in time
2hPG in a
75 g OGTT
  • Established standard
  • Predicts microvascular complications
  • Sample not stable
  • High day-to-day variability
  • Inconvenient
  • Unpalatable
  • Cost
A1C
  • Convenient (measure any time of day)
  • Single sample
  • Predicts microvascular complications
  • Better predictor of CVD than FPG or 2hPG in a 75 g OGTT
  • Low day-to-day variability
  • Reflects long-term glucose concentration
  • Cost
  • Misleading in various medical conditions (e.g., hemoglobinopathies, iron deficiency, hemolytic anaemia, severe heaptic or renal disease)
  • Altered by ethnicity and aging
  • Standardized, validated assay required
  • Not for diagnostic use in children and adolescents** (as the sole diagnostic test), pregnant women as part of routine screening for gestational diabetes***, those with cystic fibrosis or those with susected type 1 diabetes