Background The magnitude of the cardiovascular risk associated with
plasma fibrinogen concentration is influenced separately by cigarette smoking
and by low-density lipoprotein (LDL) cholesterol levels. The effects of
combinations of these factors on risk and the extent to which inclusion of the
plasma fibrinogen level further refines the risks associated with smoking and
high LDL cholesterol levels are not known.
Objective To determine the inter-relationships among all of the
three factors smoking, LDL cholesterol level and fibrinogen level with respect
to the occurrence of cardiovascular disease.
Methods The study was part of the Edinburgh Artery Study, which was
a cross-sectional random sample survey of 1592 men and women aged
55–74 years. The assessment of cardiovascular disease included recall
of diagnosis by a doctor of angina or myocardial infarction, intermittent
claudication determined by a questionnaire and measurement of ankle systolic
blood pressure.
Results The odds ratio for disease in smokers in the top tertiles of
plasma fibrinogen and LDL cholesterol levels was 7.7 (95% confidence
interval 3.0–19.8; P ≤ 0.001). Neither a
multiplicative nor a synergistic effect of the three factors on the odds of
disease was observed but the level of each contributed to the risk. For example,
in current smokers in the bottom tertile of LDL cholesterol level, the odds of
disease were 6.1 (95% confidence interval 2.2–17.0;
P ≤ 0.001) in the top tertile, 2.9
(95% confidence interval 1.0–8.6; P
≤ 0.05) in the middle tertile and 1.6 (95% confidence
interval 0.5–4.8; P > 0.05) in the bottom
tertile of plasma fibrinogen level. Subjects in the bottom tertile of plasma
fibrinogen level did not have significantly elevated (P
<0.05) risks irrespective of LDL cholesterol levels and smoking
status.
Conclusion The incorporation of plasma fibrinogen level permitted
more precise delineation of the odds of disease within categories of smoking and
LDL cholesterol concentration. These relationships need to be investigated
further in prospective studies.
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