Is there a connection between my patient’s blood type and risk of thromboembolic events?

The weight of the evidence to date seem to suggest that non-blood group O may be associated with non-valvular atrial fibrillation (NVAF)-related peripheral cardioembolic complications, myocardial infarction (MI) and ischemic stroke. 1-4

A 2015 retrospective Mayo Clinic study involving patients with NVAF adjusted for CHADS2 score found significantly lower rate of peripheral embolization in those with blood group O compared to those with other blood groups combined (3% vs 2%, O.R. 0.66, 95% CI, 0.5-0.8); rates of cerebral thromboembolic events were not significantly different between the 2 groups, however. 1

A 2008 systematic review and meta-analysis of studies spanning over 45 years reported a significant association between non-O blood group and MI, peripheral vascular disease, cerebral ischemia of arterial origin, and venous thromboembolism.2 Interestingly, the association was not significant for angina pectoris or for MI when only prospective studies were included.  Some studies have reported that the association between von Willebrand factor (VWF) and the risk of cardiovascular mortality may be independent of blood group. 5,6

Although the apparent lower risk of thromboembolic conditions in O blood group patients may be due to lower levels of VWF and factor VIII in this population 1,4, other pathways likely  play a role.7  

As for why the rate of peripheral (but not cerebral) thromboembolic events in NVAF is affected by blood group, one explanation is that because of their size, larger clots (facilitated by lower VWF levels) may bypass the carotid and vertebral orifices in favor of their continuation downstream to the “peripheral bed”.1

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  1. Blustin JM, McBane RD, Mazur M, et al. The association between thromboembolic complications and blood group in patients with atrial fibrillation. Mayo Clin Proc 2015;90;216-23.
  2. Wu O, Bayoumi N, Vickers MA, et al. ABO (H) groups and vascular disease: a systematic review and meta-analysis. J Thromb Haemostasis 2008;6:62-9.
  3. Medalie JH, Levene C, Papier C, et al. Blood groups, myocardial infarction, and angina pectoris among 10,000 adult males. N Engl J Med 1971;285:1348-53.
  4. Franchini M, Capra F, Targher G, et al. Relationship between ABO blood group and von Willebrand factor levels: from biology to clinical implications. Thrombosis Journal 2007, 5:14.
  5. Meade TW, Cooper JA, Stirling Y, et al. Factor VIII, ABO blood group and the incidence of ischaemic heart disease. Br J Haematol 1994;88:601-7.
  6. Jager A, van Hinsbergh VW, Kostense PJ, et al. von Willebrand factor, C-reactive protein, and 5-year mortality in diabetic and nondiabetic subjects: the Hoorn Study. Arterioscl Thromb Vasc Biol 1999;19:3071-78.
  7. Sode BF, Allin KH, Dahl M, et al. Risk of venous thromboembolism and myocardial infarction associated with factor V Leiden and prothrombin mutations and blood type. CMAJ 2013.DOI:10.1503/cmaj.121636.
Is there a connection between my patient’s blood type and risk of thromboembolic events?

My 65 year old patient on chronic warfarin happens to have diffuse tracheobronchial calcification on her chest X-ray. Could warfarin be the culprit?

Absolutely! Although tracheobronchial calcification (TBC) is often found as part of normal aging process in the elderly, especially women, long-term warfarin use has also been implicated as a cause of TBC, even among those with less advanced age (1-4).

In a cohort of patients 60 years of age or older, radiographic evidence of trachea and bronchi calcification was found in 47% of patients on warfarin (mean age 64 years, mean duration of treatment 6 years) compared to 19% of controls (1). A positive correlation between the duration of warfarin therapy and increased levels of calcification was also found.  Fortunately, TBC is a benign finding and has no health consequences.

As for the mechanism for this rather intriguing phenomenon, the inhibition of a vitamin K-dependent protein that prevents calcification of cartilaginous tissue seems to be the most plausible (1). Although we often think of vitamin-K dependent factors in relation to the coagulation cascade, several vitamin K-dependent proteins also play an important role in the inhibition of calcification in soft tissues and blood vessels (eg, matrix Gla protein-MGP) (5,6).

In fact, rats maintained on warfarin undergo calcification of cartilage and elastic connective tissue, while exposure of the fetus to warfarin during pregnancy is associated with calcifications in and around joints, airway and nasal cartilages (4,7). These observations further support a causative role of warfarin in inducing TBC.


Bonus Pearl: Did you know that MGP deficiency in humans is known as the Keutel syndrome, a rare autosomal recessive disease characterized by several characteristic physical features, including severe cartilage calcifications and depressed nasal bridge?

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  1. Moncada RM, Venta LA, Venta ER, et al. Tracheal and bronchial cartilaginous rings: warfarin sodium-induced calcification. Radiology 1992;184:437-39.
  2. Thoongsuwan N, Stern EJ. Warfarin-induced tracheobronchial calcification. J thoracic Imaging 2003;18:110-12.
  3. Nour SA, Nour HA, Mehta J, et al. Tracheobronchial calcification due to warfarin therapy. Am J Respir Crit Care Med 2014;189:e73.
  4. Joshi A, Berdon WE, Ruzal-Shapiro C, et al. CT detection of the tracheobronchial calcification in an 18 year-old on maintenance warfarin sodium therapy. AJR Am J Roentgenol 2000;175:921-22.
  5. Wen L, Chen J, Duan L, et al. Vitamin K-dependent proteins involved in bone and cardiovascular health (review). Molecular Medicine Reports 2018;18:3-15. \
  6. Theuwissen E, Smit E, Vermeer C. The role of vitamin K in soft-tissue calcification. Adv Nutr 2012; 3:166-173.

7.      Price PA, Williamson MK, Haba T, et al. Excessive mineralization with growth plate closure in rats on chronic warfarin treatment. Proc Natl Acad Sci  U.S.A 1982;79:7734-8.

My 65 year old patient on chronic warfarin happens to have diffuse tracheobronchial calcification on her chest X-ray. Could warfarin be the culprit?