Mistrusting the GP – DM screening

[warning – long entry]

Prior to studying medicine, J. had an incredible respect for General Practitioners (GPs). It was partly this respect he felt that physicians had that led him to do medicine. However, during this course, while rotating among the various subspecialties, he realised that many GPs were masking their inadequancies and/or were simply not up to date. It is refreshing, however, to meet that occasional family physician who admits candidly for the sake of the patient.

Take for instance, J.’s recent trip to the University Health & Wellness Centre (UHWC) for a skin condition. The doctor said, “How’s final year? Okay let’s see… Hmmm, looks like classical [skin condition]. What causes it? We see together ah…” He opens a cupboard, pulls outa dermatology text and flips to [skin condition]. It was sufficient that he could recognise it and respect J. enough to admit that he didn’t know everything like the back of his hand. After all, family physicians have a huge scope of knowledge to know, and it is hardly expected of them to be able to know everything.

Remember: he who knows not, and knows not he knows not, is a fool – shun him. Pithy quote, eh?

J. is disappointed about two recent issues with GPs – DM screening and antibiotic regimes. Let’s talk about one of them.

Diabetes mellitus screening
As a medical student, relatives like to ask questions. One such relative had just had his annual medical checkup at a private clinic and came back with a fasting blood glucose of 6.5mmol/l. According to the Ministry of Health Clinical Practice Guidelines on Diabetes Mellitus, the next step would be a 2-hour oral glucose tolerance test (2-hr OGTT) with 75g of glucose. It’s not a pleasant test. There’s the waiting time of 2 hours, the fasting prior to the test and the drinking of the glucose solution (it doesn’t taste nice).

The private health screening doctor recommended a glycosylated haemoglobin (HbA1c) test instead of the 2h-OGTT. It’s a test commonly used to assess a diabetic patient’s blood glucose control over the past 3 months (red blood cells having an average life-span of 120 days). It only requires one venepuncture, no waiting, no drinking and is definitely better for patient comfort.

Except that it doesn’t really add value to a patient who already has a fasting blood glucose test result of 6.1-6.9 mmol/l (impaired glucose tolerance). His HbA1c was 4.3, in the “Ideal” category. Here’s some literature on the matter. In particular, take a close look at No. 2 and No. 4 for their conclusions.

  1. Effectiveness of glycosylated hemoglobin, fasting plasma glucose, and a single post load plasma glucose level in population screening for glucose intolerance.
    Am J Epidemiol. 1984 Mar;119(3):431-44.
  2. Combined use of a fasting plasma glucose concentration and HbA1c or fructosamine predicts the likelihood of having diabetes in high-risk subjects.
    Diabetes Care. 1997;20:1221-1225
  3. Comparison of fasting and 2-hour glucose and HbA1c levels for diagnosing diabetes. Diagnostic criteria and performance revisited. Diabetes Care. 1997;20:785-91
  4. Usefulness of stable HbA(1c) for supportive marker to diagnose diabetes mellitus in Japanese subjects. Diabetes Res Clin Pract. 2001 Jul;53(1):41-5.

Anyway, the HbA1c isn’t completely useless. For instance, if the test had come back with an elevated HbA1c, it would have meant that it was highly likely J.’s relative was diabetic. But as it is, we cannot conclude that he isn’t. In the end, to get confirmation (i.e. high high probability), he’ll still have to do the 2h-OGTT.

Maybe this was what the GP had in mind. Or that they tend to bend over backwards to make patients, who do not have this background in medicine, feel more comfortable and thus recommend a less inconvenient test as this would directly affect their income. What if the patient goes to another doctor who recommends a HbA1c and confidently tells the patient, “You don’t have diabetes!”, making the other GP look bad by telling a relative untruth? How would the patient know? Wouldn’t the patient just think the second GP was a better doctor, being able to come to a diagnosis with a less inconvenient test?


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