The quantitative calculation of risk of coronary heart disease (CHD) has become increasingly important since the middle of the previous decade for the development of recommendations for the treatment of hypertension and hypercholesterolemia, and such calculations have been included in most of the most influential clinical practice guidelines. In addition to their practical usefulness, risk assessments are also used widely in clinical research, as seen in many articles published in Atención Primaria. By way of example, I shall cite only two recently published articles that examine the subject of CHD risk in patients with diabetes.1,2
The risk of CHD in diabetes mellitus, and the treatment of dyslipidemia with lipid-lowering drugs, are subjects of current debate, and have given rise to two conflicting stances. The Third Report of the Adult Treatment Panel III3 considers diabetes a CHD risk equivalent. In other words, a patient with diabetes is at high risk for CHD (10-year risk >=20%) because of impaired glucose metabolism. Consequently, interventions aimed at diabetes should fulfil the same treatment criteria as in patients with CHD. Moreover, because these patients are by definition at high risk, the recommended risk factor tables are not needed to calculate risk.
The recommendation of the Adult Treatment Panel III to consider diabetes mellitus as a CHD risk equivalent is not shared by other organisms. The European Societies on Coronary Prevention4 consider diabetes only as a risk factor; the sum of the scores for this and the rest of the risk factors yields the total coronary risk. Thus interventions aimed at dyslipidemia in persons with diabetes follow the same treatment recommendations as for other risk factors, and the 10-year risk is considered high at >=20%.
There are arguments in favor of and against cataloging diabetes as a CHD risk equivalent. Some prospective studies offer data that compare the risk in patients with diabetes and in patients who have suffered myocardial infaction.5 On the other hand, studies of interventions with lipid-lowering drugs in patients with diabetes but without CHD are few, and insufficient to determine whether the benefits of treatment are also equivalent to those in patients with ischemic heart disease.
Against this background of debate over the risk in patients with diabetes, Otzet et al. publish, in this issue of Atención Primaria, a study designed to determine the risk of cardiovascular disease associated with alterations in glucose metabolism as classified by the WHO-85 and the ASA-97 systems. According to these authors, there are no differences in risk of CHD or in the prevalence of risk factors between patients diagnosed as having impaired glucose tolerance according to the WHO-85 system and those found to have impaired fasting glucose with the ADA-97 system. However, agreement between the two diagnostic groups was poor. The risk of CHD increases with the degree of impairment of glucose metabolism, and is greatest when diabetes mellitus is diagnosed with either of the two systems. Otzet et al. found that between 72% and 76% --depending on which system is used-- had a 10-year risk of CHD of >=20%. On the basis of these figures, most persons with diabetes should be considered at high risk (>20% at 10 years) for CHD, as more than 70% of such individuals were found to be at high risk with calculations based on risk factor tables. However, in another article published in Atención Primaria in May 2001,2 only 31.7% of the persons with diabetes had a risk >=20%. Although the two studies did not use the same selection criteria and were based on different risk tables with data from different sources, the discrepancy in the percentages of patients with diabetes who were at high risk for CHD was so large as to raise the question: what is the risk in our own patients with diabetes? If most persons with diabetes are not at high risk, and if, in accordance with the higher estimate, they are assumed definition to have CHD risk equivalents, the resources and costs of intervention to achieve a stricter control of cholesterol values will be greater than if--in accordance with the lower figure--almost all persons with diabetes are found to have a risk >=20% based on calculations with risk tables. Thus the answer to the question posed above is not yet obvious, and further studies will be needed to reach an answer.
In connection with the risk of CHD in patients with diabetes, other questions arise which need to be answered before the criteria developed by influential international organisms can be imported without further consideration. How many persons with diabetes require lipid-lowering treatment? What doses are appropriate if these patients are assumed to have CHD risk equivalents, compared to those for whom treatment is calculated on the basis of risk tables? What would the cost be? In anticipation of the results of clinical assays that are investigating lipid-lowering treatment for the primary prevention of CHD in patients with diabetes, one final question that needs to be asked is: Do the potential benefits make lipid-lowering treatment worthwhile?
