ATLANTA — Current criteria for diagnosing metabolic syndrome fail to identify many African American patients at increased risk of cardiovascular disease and diabetes, so the criteria should be changed for those patients, said Dr. Anne E. Sumner at a meeting sponsored by the International Society on Hypertension in Blacks.
Of the three sets of diagnostic criteria currently in use, all list triglyceride levels in excess of 150 mg/dL as one sign that a patient has the metabolic syndrome. But studies show that even obese and insulin-resistant African Americans can have low triglyceride levels, said Dr. Sumner, a clinical investigator at the National Institute of Diabetes and Digestive and Kidney Diseases branch of the National Institutes of Health.
“The inclusion of triglyceride [levels] in the metabolic syndrome leads to the exclusion of a significant proportion of insulin-resistant African Americans,” Dr. Sumner said at the meeting, cosponsored by the American Society of Hypertension. On the other hand, “the exclusion of triglyceride from the metabolic syndrome criteria [would] lead to the inclusion of the significant proportion of insulin-resistant African Americans.”
Dr. Sumner relied on several clinical studies to support her conclusion. Data from the National Health and Nutrition Examination Survey (NHANES) show that both African American men and women have a significantly higher prevalence of cardiovascular disease and diabetes than do whites. Despite that, NHANES data show that African American men and women at all body-mass index levels have lower rates of metabolic syndrome than do whites.
Preliminary results from the Triglyceride and Cardiovascular Risk in African Americans study, for which Dr. Sumner is a principal investigator, show that even African Americans with very high BMIs and very high levels of insulin resistance can have very low levels of triglycerides.
She pointed in particular to 2 women among the 210 African Americans so far enrolled in the study. One has a BMI of 55 kg/m
Thirty percent of the African Americans in the study are insulin resistant, but only 2% have elevated triglycerides. In comparison, data from other studies show that about 60% of whites with insulin resistance have elevated triglycerides.
Dr. Sumner obtained similar results from her as-yet-unpublished analysis of NHANES data. She examined data from a cohort of 2,804 persons, aged 20–70, composed of 569 non-Hispanic blacks, 1,485 non-Hispanic whites, and 750 Mexican Americans. She divided the entire cohort into thirds based on their homeostasis model assessment (HOMA) scores, a surrogate for insulin resistance. Of the patients with the highest HOMA scores, the blacks had significantly lower triglyceride levels than either the whites or the Mexican Americans. This held true for both men and women as well as for individuals who were obese, overweight, and of normal weight.
Although triglyceride levels do have a direct relationship with insulin resistance, the absence of high triglyceride levels in African Americans does not mean the absence of insulin resistance. Therefore, any system that relies on triglyceride levels as a marker for insulin resistance risks underdiagnosis in African Americans. “In blacks, the danger of underdiagnosis is the lost opportunity for the prevention of diseases related to insulin resistance, particularly diabetes and heart disease,” Dr. Sumner said.
She suggested the solution is to develop criteria for “triglyceride-absent metabolic syndrome” to be used in African Americans and to test prospectively whether requiring just two of the four remaining criteria (waist circumference, hypertension, low HDL cholesterol, and high fasting glucose) for the diagnosis of metabolic syndrome would accurately predict the onset of diabetes or cardiovascular disease.
For the those in Dr. Sumner's study, the definition of metabolic syndrome developed by the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) results in a prevalence of 11%, a sensitivity of 21%, and a specificity of 97%. With the triglyceride-absent definition, the prevalence would be 30%, the sensitivity would be 53%, and the specificity would be 81%. “I felt this [triglyceride-absent definition] was a minimalist approach to the changing of the metabolic syndrome with the smallest perturbation,” she said.