Air pollution and INR
VERONA, ITALY. Many afibbers taking warfarin (Coumadin) for stroke prevention experience problems keeping their INR (International Normalized Ratio) within the prescribed range of 2.0 to 3.0. Diet, especially the intake of vegetables with dark, green leaves (excellent sources of vitamin K), can markedly affect INR and, according to a recent study carried out by a team of Australian and Italian researchers, so can air pollution.

Air pollution is a multi-headed beast. It is basically a heterogeneous mixture of solid and liquid particles suspended in air. Some common sources are car emissions, road dust, tire abrasion, power generation, pollen, moulds, and forest fires. The effects of air pollution on humans include inflammation, oxidative stress, dysfunction of the autonomic nervous system, adverse cardiovascular events, and inappropriate activation of the body's blood clotting mechanism. There is now evidence that even short-term exposure to air pollution, particularly diesel exhaust fumes and ultra-fine particles (less than 2.5 micrometers in diameter) can result in hypercoagulability (accelerated blood clotting), and thus increase the risk of ischemic stroke. Exposure to diesel exhaust has been found to increase the blood level of fibrinogen and plasminogen activator inhibitor-1, while decreasing the level of plasminogen activator. These changes all decrease prothrombin time (the measurement expressed as INR) and thus accelerate clot formation. Furthermore, there is also evidence that ultra-fine particles induce platelet accumulation, adding yet another potential stroke risk factor to the picture.

The Australian/Italian research team conclude that the extent of air pollution in an area may significantly affect not only actual clotting tendency, but also the results of the INR test – air pollution would presumably lower the value. They suggest that such factors as ethnicity, smoking, diet, exercise, and air pollution should be taken into account when interpreting INR results, but concede that this is unlikely to become common practice any time soon.

Lippi, G, et al. Air pollution and coagulation testing: a new source of biological variability? Thrombosis Research, Vol. 123, 2008, pp. 50-54