Patients with coagulopathies may present with a variety of clinical signs based on not only the underlying disease process, but also the type of coagulopathy. Whenever a medical process can be confusing or complex, the VETgirl team likes to break it down into easy to evaluate thinking points.
When you evaluate the process of hemostasis, it is commonly divided into primary hemostasis and secondary hemostasis.
- Primary hemostasis refers to the formation of the platelet plug
- Secondary hemostasis refers to formation of the stable fibrin clot.
(If you want to get a little more technical, the third component of hemostasis is fibrinolysis, which refers to the breakdown of the clot.)
The process of primary hemostasis involves the initial formation of the platelet plug, including platelets, the vascular endothelial cells, von Willebrand's factor, red blood cells, and white blood cells.
Disorders of primary hemostasis include thrombocytopenia (decreased platelet count) and thrombocytopathia (decreased platelet function).
Clinical signs of a primary hemostatic disorder typically result in surface bleeding, notably petechia, ecchymoses and mucosal surface bleeding (e.g. gingival bleeding, gastrointestinal surfaces, and urogenital surfaces).
Useful diagnostic tests to detect primary hemostatic disorders include:
1. Platelet estimate (blood smear) and count (automated or manual):
- 1 platelet per oil immersion 100x = 12,000-15,000 platelets (NOTE: If the platelets are clumped, an accurate count cannot be obtained.
2. Platelet machine count (CBC machine or hemocytometer)
3. Buccal mucosal bleeding time (BMBT)
4. Bone marrow evaluation
5. Von Willebrand factor assay
The process of secondary hemostasis results in the formation of fibrin through a series of enzymatic reactions involving coagulation factors, cofactors, calcium, and phospholipid membranes.
Disorders of secondary hemostasis include abnormalities within the coagulation cascade. As compared to abnormalities of primary hemostasis that results in surface bleeding, patients with disorders of secondary hemostasis present with signs consistent with cavity bleeding, including the abdominal cavity, pleural space, subcutaneous or intramuscular hematomas, and mucocutaneous bleeding.
Useful Diagnostic Test to Detect Secondary Hemostatic Disorders
1. Intrinsic and Common Pathways
- Activated Clotting Time (ACT)
- Activated Partial Thromboplastin Time (aPTT)
2. Extrinsic and Common Pathways
- Prothrombin Time (PT)
- Protein Induced by Vitamin K Antagonism or Absence (PIVKA)
Regardless of the hemostatic defect, the approach to the bleeding patient is directed at providing hemostasis, providing appropriate therapy, and performing the necessary diagnostic tests to determine the underlying cause.