Prevalence of low ankle-brachial index, elevated plasma fibrinogen and CRP across Framingham risk categories: Data from the National Health and Nutrition Examination Survey (NHANES) 1999–2004

Abstract

Objective60–80% of heart attacks or coronary-related deaths occur in individuals identified as non-high-risk per the conventional risk assessment algorithms. Abnormal ankle-brachial index (ABI), plasma fibrinogen and plasma C-reactive protein (CRP) have been shown to be associated with a higher risk of cardiovascular disease (CVD). However, comparable data have not been reported for prevalence of abnormal ABI, fibrinogen and CRP in non-high-risk population. MethodsWe analyzed data from the 1999–2004 National Health and Nutrition Examination Survey (NHANES), a nationally representative cross-sectional survey of the U.S. population, for 6292 men and women, aged 40 and older, without known CVD or diabetes, with available data on standard CVD risk factors, ABI, fibrinogen and CRP. The main objective was to identify proportions of individuals with abnormal ABI (ABI<0.9 in either leg), elevated fibrinogen (≥400mg/dl), and elevated CRP (>3mg/l), with otherwise low or intermediate (<20%) 10-year Framingham risk score. ResultsOverall prevalence of abnormal ABI, fibrinogen, and CRP was 3.6% (95% CI 3.2–4.1%), 27.4% (95% CI 23.9–31.0%) and 38.3% (95% CI 36.5–40.0%) respectively. Among those with ABI data, 91.4% were at <20% FRS, and of these only 2.7% (95% CI 2.3–3.1%, p<0.0001) had an abnormal ABI. Among those with fibrinogen data, 90.8% were at <20% FRS, and of these 23.6% (95% CI 20.4–26.8%, p<0.001) had elevated plasma fibrinogen. Among those with CRP data, 91.1% were at <20% FRS, and of these 34.3% (95% CI 32.7–36.0%, p=0.0012) had an elevated CRP. Overall, 45.0% (95% CI 42.2–47.8%; p<0.0001) had abnormal ABI, fibrinogen or CRP but low-intermediate risk. ConclusionAbnormal ABI, elevate fibrinogen and CRP are highly prevalent among individuals otherwise at low-intermediate risk. If any or all of them are shown to improve predictive ability of FRS for primary prevention, it would have a significant public health impact.