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.

2018 Diabetes Canada 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 and not for suspected type 1 diabetes (see text)

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 result 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 a confirmatory test is not required before treatment is initiated. If results of 2 different tests are available and both are above the diagnostic thresholds, the diagnosis of diabetes is confirmed.

To avoid rapid metabolic deterioration in individuals in whom type 1 diabetes is likely (younger or lean or symptomatic hyperglycemia, especially with ketonuria or ketonemia), the initiation of treatment should not be delayed in order to complete confirmatory testing.

2hPG, 2-hour plasma glucose; AlC, glycated hemoglobin; 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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