The power of a well drawn Venn diagram to show how a diagnostic criteria can change the number of people diagnosed as diabetic.

Bismillah,  alhamdulillah: Sometimes a picture is worth a thousand words. This Venn diagram nicely illustrates how changing the diagnostic criteria for diabetes will affect the epidemiology of diabetes. A new set of patients will fall under the label of diabetes and some old timers will loose the label. The sceptics might note that overall the number of diagnosed diabetics will go up significantly and pharmaceutical sales of medication will no doubt reflect that. As a clinician who sees significant variability and mismatch between fasting glucose and HbA1c, especially in the Middle East, I sit firmly in the old timers camp and rely on the older more pathophysiologically consistent diagnostic criteria. I am sure the debate between experts over the issue has not ended. I have three thoughts that come to mind if the HbA1c is adopted:

  1. If we accept HbAc as a diagnostic criteria what should we say to patients who had a HbA1c >6.5% but a normal FG who then manage to normalise their HbA1c through lifestyle changes. Did the lifestyle prevent diabetes or cure it? If we are consistent we should surely say – cure. Great news we have discovered a cure for diabetes! Indeed the pen is mightier than the sword.
  2. Will clinicians behave in a paternalistic way and start to hunt for diabetes by any criteria? Instead of relying on a single criteria could this, coupled with the falling cost of tests and Health Information Systems offering ‘one click ordering’, result in more than one test done at a time. Will we have a rule-in or a rule-out attitude? I suspect a rule-in one is where doctors tend to head for. We will then have the ability to increase the incidence of diabetes from 9.1% of the population to 19.9% of the population. A small step for doctors, a giant leap for mankind.
  3. No one seems to talk about the clinical value of the extra diagnoses over a period of time. A patient who is diabetic by HbA1c but not by fasting glucose today, and is truly destined to have diabetes will eventually have both criteria being positive after a period of time. What is that period of time? Is the earlier diagnosis clinically significant rather than statistically significant? Do we have long term studies that have tracked these two populations from pre-diagnosis and onwards?

My gut feeling is that the race between HbA1c and fasting glucose sounds like the old turtle and hare race story: at the end of the day the slower predictable turtle of fasting glucose will win over the faster but unpredictable hare.

The Venn diagram was taken from the following article:

Focus: HbA1c and postprandial glucose: should they be used as diagnostic criteria or only for monitoring glycemic control?

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