In this VETgirl online veterinary continuing education blog, Dr. Garret Pachtinger reviews the rare but potentially deadly coagulopathy, hemophilia. Is this a coagulopathy that can be easily picked up on a PT and aPTT clotting test in the veterinary emergency room?
In both general practice and the emergency room alike, hemorrhage is a common and concerning condition. Patients may present with a variety of clinical signs as well as a varied degree of stability. The diagnosis may be easy, such as with trauma and external hemorrhage, or it may be more of a diagnostic challenge with vague signs of illness including lethargy and loss of appetite.
In veterinary school we are taught that defects in primary hemostasis (e.g., thrombocytopenia/ thrombocytopathia) will result in surface bleeding (e.g. petechia or ecchymosis) and disorders of secondary hemostasis (e.g., coagulation factors) will result in cavity bleeding (e.g. hemoabdomen, hemothorax, etc.).s
That said, we don't live inside of a textbook. In real life we know that defects in primary hemostasis (e.g., thrombocytopenia/thrombocytopathia) can also result in cavity bleeding and disorders of secondary hemostasis (e.g., coagulation factors) can also result in surface bleeding!
While VETgirl has had previous sessions on hemostasis, we wanted to talk today about a less common although important coagulation abnormality - hemophilia. There are two common classifications of Hemophilia, Hemophilia A and Hemophilia B. Hemophilia A is factor VIII (8) deficiency commonly described in the German shepherd dog. Hemophilia B is factor IX (9) deficiency.
Hemophilia A is a sex-linked hereditary, recessive disorder affecting male dogs only. Understanding that Factor VIII is a component of the intrinsic clotting cascade pathway, it is possible that affected patients will have a prolonged PTT (with a normal PT). With that said, there is poor correlation between the prolongation of PTT and estimation of the deficiency of factor VIII and a patient may have a PT and PTT within the normal range and still clinically bleed with Hemophilia. In affected patients, factor VIII levels are often less than 20% of normal factor activity. To confirm the diagnosis, coagulation factor testing is necessary to determine which factor is abnormal.
Here is an example of a clinical patient with Hemophilia A.
A 2.5 year old male intact Dachshund presented to the ER with a concern for a "lump" on the back and bruising on the abdomen. On FNA, the lump was aspirated and determined to be blood / hemorrhage.
Coagulation testing was performed:
As the initial bloodwork did not show a cause for the bleeding, and understanding this patient was an intact, male patient (e.g., had never experienced surgery before), hemophilia was a differential.
Blood was submitted to the Comparative Coagulation Laboratory at Cornell University confirming the diagnosis of Hemophilia.
Unfortunately management of dogs with hemophilia is difficult. Currently, the only treatment is transfusion with fresh frozen plasma (FFP) or cryoprecipitate. Factor VIII is contained in both fresh frozen plasma and cryoprecipitate.
NOTE: cryoprecipitate does not contain factor IX, so this would not be a suitable treatment for patients with hemophilia B.