Coronary artery disease and elevated serum fibrinogen were stronger predictors of peripheral vascular disease in subjects younger than 60 years than in older subjects, according to a study that used the results of the National Health and Nutrition Examination Survey 1999–2002 to evaluate a variety of possible risk factors.
Chronic renal insufficiency was more highly predictive of peripheral vascular disease (PVD) in subjects aged 60 years and over, according to Dr. Louis M. Messina and colleagues at the University of California, San Francisco. Their analysis was presented at the annual meeting of the Western Vascular Society, Deer Valley, Utah. The investigators used the NHANES data to determine the prevalence of premature PVD in the U.S. population, and they used presumptive risk factors as covariates to model the occurrence of the condition.
PVD in patients under age 60 years is considered premature, according to the researchers. Premature PVD is associated with an extremely poor prognosis, including high rates of cardiovascular morbidity, limb loss, and premature death. Previous studies have been small, have dealt only with a limited number of risk factors, and focused on coronary vascular disease as the outcome of interest, according to the researchers.
Based on the hypothesis that there was an interaction between risk factors and age, the investigators analyzed the data to compare the population aged less than 60 years (mean age 49) with those 60 years and older (mean age 70).
NHANES began to provide data in 1999 from detailed lower extremity examinations, including measurement of the ankle-brachial index (ABI). An ABI of less than 0.9 was considered indicative of lower peripheral vascular disease, according to the researchers, and was correlated with the other variables collected in the sampled population. Previous research has shown that a low ABI is one of the strongest predictors of cardiovascular morbidity and all-cause mortality.
The investigators compared data from 2,498 patients under age 60 with those from 2,585 patients aged 60 years and older. Peripheral vascular disease rates were approximately 2% in the younger group and 12% in the older group.
A history of coronary artery disease appeared to be highly predictive of PVD in the population under age 60. The odds ratio was 2.9 for this younger group, compared with approximately 1.3 for the older population.
In an analysis of the other possible risk factors, the researchers found that a 10-mg/dL increase in fibrinogen was associated with a 7% increase in odds in subjects under age 60, compared with a 3% increase in patients 60 years and older.
Although the authors did not believe this result was sufficient to indicate wide-scale screening of high fibrinogen levels to detect PVD, they did suggest that it may have clinical relevance for secondary intervention, since fibrates and niacin can lower fibrinogen levels.
In contrast, a decreased creatinine clearance was significantly associated with PVD in individuals aged 60 and older, with a 10-unit decrease in clearance affording a 16% increase in the PVDodds ratio. There was no significant correlation in the younger age group, the researchers reported.
Strong risk factors that are independently associated with PVD regardless of age category include smoking and hypertension. Metaanalysis of plasma homocysteine levels showed only a weak association with the development of PVD.
Although there was no difference found in risk associated with gender between the age groups, being male was a significant overall predictor (odds ratio slightly greater than 2.0).
“That premature peripheral vascular disease is associated with elevated fibrinogen suggests what many had suspected but not proven, that premature PVD is associated with a 'hypercoagulable state.' It was important to confirm this in a large population-based study. The other important risk factor was the presence of coronary artery disease. That coronary artery disease correlated more closely with premature peripheral vascular disease in those less than 60 years of age is equally surprising,” Dr. Messina added.
Information on NHANES and its data sets is available at www.cdc.gov/nchs/nhanes.htm