Screening for and Diagnosing Diabetes

Healthcare Provider Tool

Reset

Measure Fasting Plasma Glucose (FPG) and/or A1C and enter test results:

  mmol/L     %

Or

Measure 75g Oral Glucose Tolerance Test (OGTT) and enter test results:

  mmol/L     mmol/L
Calculate Screening / Diagnosis Result
Calculate

Not enough information is provided

Rescreen as recommended, every 3 years.

ERROR

Enter value for FPG and/or A1C; or OGTT only.

Normal

(Re)screen as recommended

At risk for prediabetes and type 2 diabetes

Rescreen more often

Prediabetes

Rescreen more often

Diabetes

Tests are discordant

The patient may have diabetes, suggest repeat A1C. If patient has symptoms of hyperglycemia, confirmatory / repeat test is not required, consider patient to have diabetes.

Tests are discordant

The patient may have diabetes, suggest repeat FPG. If patient has symptoms of hyperglycemia, confirmatory / repeat test is not required, consider patient to have diabetes.

Normal

IGT (prediabetes)

Possible diabetes

Confirmatory test required. If patient has symptoms of hyperglycemia, confirmatory / repeat test is not required, consider patient to have diabetes.

Diabetes

IFG (prediabetes)

IFG and IGT (prediabetes)

This test is normal

(Re)screen as recommended

This represents someone at risk

Consider A1C test, rescreen more often

This represents prediabetes

Consider A1C test, rescreen more often

This might represent diabetes

Requires second test for confirmation, consider repeat FPG and / or A1C test. If patient has symptoms of hyperglycemia, confirmatory / repeat test is not required, consider patient to have diabetes.

This represents someone at risk

Consider FPG test, rescreen more often

This represents prediabetes

Consider FPG test, rescreen more often

This might represent diabetes

Requires second test for confirmation, consider repeat A1C and / or FPG. If patient has symptoms of hyperglycemia, confirmatory / repeat test is not required, consider patient to have diabetes.

Review Clinical Practice Guidelines' Chapter 4: Screening for Type 1 and Type 2 Diabetes for more detailed information.

  • 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.

  • 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

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
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
 
 
This is only to be used as a decision support tool and is subject to these terms.
For more information, please see terms of use.
 

*The Canadian Diabetes Association is the registered owner of the name Diabetes Canada. All content on guidelines.diabetes.ca, CPG Apps and in our online store remains exactly the same. For questions, contact communication@diabetes.ca.