Stemcell Safarivet

Pulmonary Thromboembolism and Immune Mediated Hemolytic Anemia (IMHA)


Steven Garner DVM, DABVP
Chief of Staff
Safari Veterinary Care Centers
League City, Texas 77573

Blood clots are a symptom of Immune Mediated Hemolytic Anemia (IMHA) and it is important to understand the role they play as you are dealing with this disease. In fact, blood clots in the lungs are the most common finding in dogs that died from IMHA (1) (2) (3) .

The clotting factors that make the blood clot are produced in the liver. Clotting factors are chemicals that are inactive and float around in the blood just waiting for the signal to come together holding hands to form a net across any rents (holes) they find in blood vessels. They form these nets in order to catch platelets and red blood cells to help them form a clot to patch up the hole. These clotting factors hold hands like a group of skydivers coming together to form an interconnected web.

Activation of this “clotting cascade” is stimulated by red cell lysis (death.) (1) As the blood circulates, it must pass through the lungs. In the lungs, blood cells pass from veins to arteries in sinusoids that surround the alveoli of the airways. Because these sinusoids are very tiny, the blood must flow slowly, which means blood clots and fibrin clots can form very easily.

Because IMHA causes activation of this clotting cascade, most of these fibrin clots occur in the lungs. The liver is overtaxed because it must process more dead or dying red blood cells than it normally does, yet it is also being asked to produce more clotting factors than it normally does. The lack of the liver’s ability to produce enough clotting factors causes an imbalance of clotting and bleeding – all of which are happening in the lungs, resulting in pulmonary thrombosis, or blood clots. This thrombosis in the lungs is a very common cause of death in many IMHA dogs (2) .

Your veterinarian should prescribe a blood clot inhibitor or blood thinner such as heparin, clopidogrel (Plavix) or a low dose of aspirin (2) to try to prevent the clotting from becoming a serious problem.

Studies show that stem cells facilitate thrombus (clot) resolution. Stem cells are naturally recruited by the body to resolve blood clots in veins (3) . Stem cells promote the outgrowth of new blood vessels facilitating the resolution of blood clots (4) . Stem cells promote the recanalization of vessels blocked by clots (5) .
While there are also research related concerns about increased blood clots in some cases treated by stem cells (1) . At Safari, we have seen dramatic positive effects from the administration of stem cells to pets with lung blood clots secondary to IMHA. These effects promote resolution of the blood clots in the lungs potentially saving the lives of some pets with IMHA.


  1. Hemostatic abnormalities in dogs with primary immune-mediated hemolytic anemia. Scott-Moncrieff JC, Treadwell NG, McCullough SM, et al:. 3, 2001, JAAHA, Vol. 37, pp. 220-227.
  2. Prognostic factors for mortality and thromboembolism in canine immune-mediated hemolytic anemia: A retrospective study of 72 cases. Carr AP, Panciera DL, Kidd L. 5, 2002, J Vet Intern Med, Vol. 16, pp. 504-509.
  3. Pulmonary thromboembolism associated with immune-mediated hemolytic anemia in dogs: Ten cases (1982-1987). Klein MK, Dow S, Rosychuk R. 2, 1989, JAVMA, Vol. 195, pp. 246-250.
  4. Canine Immune-Mediated Hemolytic Anemia: Treatment and Prognosis. Andrea Balch, DVM, MS, DACVIM,Andrew Mackin, BVMS, DACVIM. s.l. : Compendium, April 2007, Compendium.
  5. Endothelial progenitor cells are recruited into resolving venous thrombi. Modarai B, Burnand KG, Sawyer B, Smith A,. 1, 2005, Circulation, Vol. 11, pp. 2645-2653.
  6. The role of neovascularization in the resolution of venous thrombus. Modarai B, Burnand KG, Humphries J, Waltham M, Smith A,. 2005, Thromb Haemost, Vol. 93, pp. 801-809.
  7. Cell-based therapy facilitates venous thrombus resolution. Santo SD, Tepper OM, von Ballmoos MW, Diehm N, Volzmann J, Baumgartner I, et al. 2009, Thromb Haemost, pp. 460-464.
  8. Tissue factor triggers procoagulation in transplanted mesenchymal stem cells leading to thromboembolism. Kohei Tatsumi, KazuoOhashi, Yoshinori Matsubara, Ayako Kohori, Takahiro Ohno, Hiroshi Kakidachi, Akihiro Horii, Kazuko Kanegae, Rie Utoha, Takanori Iwata, Teruo Okano. 2, s.l. : Elseivier, 2013, Biochemical and Biophysical Research Communications, Vol. 431, pp. 203-209.