What if the 2 Tests are Discordant?

Case Study

Mr. D.R. is 47 years old with longstanding obesity.

Screening tests for type 2 diabetes are done:

  • FPG: 6.3 mmol/L
  • A1C: 6.7%

Should you tell Mr. D.R. that he has type 2 diabetes?

Yes No

Click here to see the Diagnostic Crieria for Diabetes

Reveal Answer

You are correct!

Mr. D.R. has an A1C of 6.7%, which is above the cutpoint for diabetes diagnosis, but a FPG of 6.3 mmol/L, which is in the category of prediabetes (IFG).

To be diagnosed with type 2 diabetes, a confirmatory test must be done on another day.

No, not yet.

Mr. D.R. has an A1C of 6.7%, which is above the cutpoint for diabetes diagnosis, but a FPG of 6.3 mmol/L, which is in the category of prediabetes (IFG).

To be diagnosed with type 2 diabetes, a confirmatory test must be done on another day.

2013 CDA Updated Diagnostic Criteria for Diabetes

FPG ≥ 7.0 mmol/L
Fasting = no caloric intake for at least 8 hours

or

A1C ≥ 6.5% (in adults)
Using a standardized, validated assay, in the absence of factors that affect the accuracy of the A1C (Not for diagnostic use in children, adolescents, pregnant women or suspected type 1 diabetes. Misleading in hemoglobinopathies, iron deficiency, hemolytic anemia, severe liver or renal disease. Altered by aging and ethnicity.)

or

2hPG in a 75-g OGTT ≥ 11.1 mmol/L

or

Random PG ≥ 11.1 mmol/L
Random = any time of the day, without regard to the interval since the last meal

In the absence of symptomatic hyperglycemia, if a single laboratory test is in the diabetes range, a repeat confirmatory laboratory test (FPG, A1C, 2hPG in a 75-g OGTT) must be done on another day. It is preferable that the same test be repeated (in a timely fashion) for confirmation, but a random PG in the diabetes range in an asymptomatic individual should be confirmed with an alternate test. In the case of symptomatic hyperglycemia, the diagnosis has been made and confirmatory test is not required before treatment is initiated. In individuals in whom type 1 diabetes is likely (younger or lean or symptomatic hyperglycemia, especially with ketonuria or ketonemia), confirmatory testing should not delay initiation of treatment to avoid rapid deterioration. If results of two different tests are available and both are above the diagnostic cutpoints, the diagnosis of diabetes is confirmed.

2hPG = 2-hour plasma glucose; FPG = fasting plasma glucose; OGTT = oral glucose tolerance test; PG = plasma glucose

Which test will you repeat to confirm the diagnosis of type 2 diabetes?

FPG A1C FPG and A1C

Click here to see how to handle discordance amongst different tests of glycemia.

Submit

You are correct!

Because of discordance between the A1C (6.7%) and FPG (6.3 mmol/L), the test that is above the diagnostic cutpoint (A1C) should be repeated.

Repeat A1C is 6.6%

Diagnosis of type 2 diabetes is confirmed.

That answer is incorrect.

Because of discordance between the A1C (6.7%) and FPG (6.3 mmol/L), the test that is above the diagnostic cutpoint (A1C) should be repeated.

Repeat A1C is 6.6%

Diagnosis of type 2 diabetes is confirmed.

How to Handle Discordance:

If results of two different tests are available and both are above the diagnostic cut-points, the diagnosis of diabetes is confirmed. When results of more than one test are available (amongst FPG, A1C, 2hPG in a 75-g OGTT) and the results are discordant, the test whose result is above the diagnostic cut-point should be repeated, and the diagnosis is made on the basis of the repeat test.

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