Canadian HbA1c Threshold for Diagnosing Diabetes
In Canada, diabetes is diagnosed when HbA1c is ≥6.5% (48 mmol/mol), measured using an NGSP-certified laboratory method and confirmed with repeat testing. 1
Diagnostic Criteria
The Canadian guidelines, as referenced by Diabetes Canada 2016, align with international standards for HbA1c-based diabetes diagnosis:
- HbA1c ≥6.5% (48 mmol/mol) is the diagnostic threshold for diabetes 1
- The test must be performed in a certified laboratory using an NGSP-standardized method traceable to the DCCT assay 1
- Confirmation with repeat testing is required unless the patient presents with unequivocal hyperglycemia (hyperglycemic crisis or classic symptoms with random glucose ≥11.1 mmol/L) 1, 2, 3
Confirmation Algorithm
When using HbA1c to diagnose diabetes in Canada, follow this structured approach:
Initial Testing
- Obtain HbA1c from a certified laboratory (not point-of-care) 1, 4
- If HbA1c ≥6.5%, repeat testing is mandatory before confirming diagnosis 2, 3
Confirmatory Testing Options
Preferred approach: Repeat the same HbA1c test, as this provides greater concordance 3
Alternative approach: Use a different test (fasting plasma glucose or 2-hour OGTT) 3
Timing of Confirmation
- Perform confirmatory testing without delay (within days to weeks) for results clearly above threshold 2, 3
- For borderline results near 6.5%, repeat testing in 3-6 months is acceptable 3
When HbA1c Cannot Be Used
Canadian guidelines recognize specific situations where only glucose-based criteria (fasting glucose ≥7.0 mmol/L or 2-hour glucose ≥11.1 mmol/L) should be used for diagnosis:
- Hemoglobinopathies (sickle cell disease, HbS, HbC variants) that interfere with HbA1c measurement 1, 4
- Conditions with altered red blood cell turnover: 1, 4
- Pregnancy (second and third trimesters)
- Hemodialysis or chronic kidney disease
- Recent blood loss or transfusion
- Hemolytic anemia
- Erythropoietin therapy
- Iron deficiency anemia
In these scenarios, use fasting plasma glucose ≥7.0 mmol/L or 2-hour OGTT ≥11.1 mmol/L as diagnostic criteria 1
Screening Context in Canada
For stroke patients specifically, Canadian Stroke Best Practice guidelines recommend screening with:
- Fasting plasma glucose, OR
- 2-hour plasma glucose, OR
- HbA1c (A1C), OR
- 75g oral glucose tolerance test 1
This demonstrates that HbA1c is an accepted screening and diagnostic tool across Canadian clinical contexts 1
Population-Based Evidence from Canada
A nationally representative Canadian study (2007-2011) found that using HbA1c ≥6.5% identified significantly more undiagnosed diabetes cases (3.09% prevalence) compared to fasting glucose alone (1.13% prevalence), representing 41% versus 20% of total diabetes cases respectively 5. This supports the diagnostic utility of the HbA1c threshold in the Canadian population.
Critical Pitfalls to Avoid
- Never diagnose diabetes on a single HbA1c value without confirmation, unless hyperglycemic crisis is present 1, 2, 3
- Do not use point-of-care HbA1c devices for diagnostic purposes; only certified laboratory methods are acceptable 1, 4
- Do not apply HbA1c criteria when conditions affecting red blood cell turnover are present 1, 4
- Ensure proper sample handling: marked discordance between HbA1c and glucose levels should prompt investigation of assay interference 1
- Do not delay confirmation for months when initial results clearly exceed 6.5%; repeat testing should occur promptly 2, 3
Prediabetes Threshold
While not the primary question, Canadian guidelines also recognize: