Indian Write- Ups
| Diagnosis |
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| The New American Diabetes Association Criteria For Diagnosis of Diabetes: Clarity Or Confusion? |
| - Dr. S. M. Sadikot |
| Consultant Physician & Endocrinologist |
| What was the need to have a review of the criteria? |
| In the WHO criteria which is in use, it is necessary to use on OGTT. People who show a fasting venous plasma glucose levels 140mg% or a 2 hour venous plasma glucose value > 200mg%, or both, were classified as being diabetic. |
| Now let us first consider why these cut off points were used. |
| Plasma glucose values are distributed over a continuum and therefore there cannot be an absolute cut off point for the diagnosis. There is no definitive value, which will allow a clear discrimination between those who are classified as having diabetes and the rest. The aim of classifying people with diabetes was to delineate people who were at an increased risk for the development of adverse outcomes in relation to the long-term diabetes complications. Based in part on studies, which showed the threshold for micro-vascular disease WHO chose the FPG and the 2 hour PG values. |
| In essence it became the 2 hour-PG value which was the important criteria, as all patients who had a FPG value 140mg% showed a 2 hour-PG >200mg%. |
| The cut off point of the 2 hour-PG value was justified on the grounds that it was approximately at this value that some of the micro-vascular complications of diabetes such as nephropathy and retinopathy increased significantly. Similar considerations were behind the use of a FPG value of 140mg%. Thus the cut off were based on thresholds for micro-vascular disease available at that time. |
| But a closer look at all the OGTT studies which have been reported showed that though all the people who had a FPG value 140mg% showed a 2 hour PG value > 200mg%, only one fourth of those who had 2 hour-PG values > 200mg%, and without a previous diagnosis of diabetes, showed a FPG value 140mg%! Using a FPG value of 140mg% defined a level of hyperglycemia which was greater than that defined by a m hour-PG value of 200mg%. This was unacceptable, as both the values should define almost similar values of hyperglycemic load and potential for adverse outcomes. |
| In recent years new data has become available from population studies about the adverse outcomes of long-term complications. Many studies have shown that there is an increased risk for the development of micro-vascular, and even macro-vascular, disease in people who have a FPG 126mg% as compared to the risk in people who have a FPG value of 126mg%, but less than 140mg%. In other words, if the aim is to delineate persons at risk for adverse outcomes associated with long-term diabetes complications, then the use of 140mg% as the fasting cut off point meant that many people who were at risk for the adverse outcomes remained undiagnosed. |
| This is unacceptable for many reasons. Today, we know that the earlier the onset of the long-term complications of diabetes are recognised, there is more possibility that we may be able to take therapeutic measures which will allow us, if not to reverse, at least slow down the rate of progression of the complications. Therefore, it becomes essential that the long-term complications be recognised at the earliest. But if this be so, it becomes axiomatic that a diabetic be recognised at the earliest! The use of 140mg% does not allow this to happen whilst the use of 126mg% as the fasting cut off point which allows more people at risk for adverse outcomes to be identified earlier, should be a better criteria. |
| Do the new criteria also imply that there is little need to do an OGTT? The Expert Committee of the ADA has not recommended that the OGTT be done away with. But if the new FPG criteria have similar predictive values about the adverse outcomes, then one must re-examine the routine use of, and need for, an OGTT in the diagnosis of diabetes. |
| Moreover, from a practical viewpoint, the administration of an OGTT is time and labor intensive, causes inconvenience to the patients and is costly. Besides the obvious logistical difficulties and expenses, which can be overcome if necessary, the major drawback of the OGTT is its reproducibility. Studies have shown that the reproducibility is as low as 50%, which for any diagnostic test is unacceptable. This leads to a need for repeat OGTTs. Different results at different times confuses rather than clarifies. By contrast, the classification of diabetes based on the ADA criteria has been shown to have a reproducibility of almost 91%, reflecting the lower intra- individual CV of the FPG compared to the 2 hour-PG. |
| In fact, for community based epidemiological studies of prevalence, it is now widely accepted that only a FPG will suffice, if there are logistical and economic reasons. It must be realised that some of the individuals who would be diagnosed by the 2 hour PG value may be missed and others who may not have been diagnosed by the older FPG criteria may now be diagnosed as having diabetes. Thus, the overall prevalence may be slightly different. |
| If the OGTT is not carried out, people with IGT will not be diagnosed. The Expert Committee of the ADA has introduced a new term "Impaired Fasting Glucose (IFG)" for those people who show a FPG of 110mg%, but less than 126mg%. A FPG < 109mg% is considered as being in the normal range. Although this figure has been chosen some-what arbitrarily, it is based on data which shows that this is the level above which the acute phase insulin secretion is lost in response to an intravenous glucose load, and is also associated with an increasing risk for developing micro-vascular and macro-vascular complications. |
| The new recommendations made by the Expert Committee of the ADA should be welcomed. The ADA has done a significant service to the cause of diabetes by bringing out the need for the new criteria. At the same time, where was the need for such unilateral declarations? Could it not have worked in concert with the International Diabetes Federation and the WHO to evolve a worldwide consensus? |
| So, it does merit a lot of "bouquets", but a few "brickbats" may not be a bad thing! |
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