Hemotological ECC Flashcards
Metabolism of RBC’s
Primarily through anaerobic glycolysis and hexose monophosphate shunt
Feline RBC’s
- more susceptible to oxidation injury and Heinz body formation than canines
- contains high percentage of sulfur-containing amino acids
What factors affect the amount of RBC’s circulating at any given time?
- Plasma volume
- Splenic contraction
- Erythropoietin (EPO)
- Rate of production from bone marrow
- Rate of destruction or loss
What hormones play a part in maintaining the RBC numbers?
- pituitary
- thyroid
- adrenal cortex
What is a normal PCV for canine?
37-55%
Normal PCV for felines?
35-45%
What is the term used for total increase in RBC count or PCV?
Polycythemia
When does a relative polycythemia occur?
In cases of severe dehydration. The TP will also be elevated
How is Hemoglobin usually calculated?
It is usually 1/3 of the PCV in g/dL
What terms do you use to determine the types of anaemia?
Mean corpuscular volume (MCV)
Mean corpuscular hemoglobin (MCH)
Mean corpuscular hemoglobin concentration (MCHC)
Mean corpuscular volume (MCV)
*Mean volume of a group of erythrocytes by diving PCV by RBC count and multiply by 10
*Canine: 60-77
*Feline: 39-55
*Normocytic: RBCs normal sized
Macrocytic: RBCs larger than normal
Microcytic: RBC smaller than normal = usually indicate iron deficiency
Mean corpuscular hemoglobin (MCH)
Mean weight of hemoglobin contained in the average RBC
*divide hemoglobin concentration by RBC count and multiplying by 10
*Normal canine: 19-23
Feline: 13-17
*Not as accurate as MCV measurements
Mean corpuscular hemoglobin concentration (MCHC)
- Concentration of hemoglobin in the average erythrocyte
- Cal by divining hemoglobin concentration by PCV and multiplying by 100
- Normal MCHC = normochromic anaemia
- Low MCHC = hypochromic state of anaemia, also likely due to low iron levels
Primary hemostasis
- Is a complex interaction between platelets, blood vessels and coagulation cascade
- Goal is to form a clot
- Effective primary hemostasis depends on adequate platelets, adequate platelet function, vessel wall integrity and von Willebrand factor (vWf)
- Vessels: initial reaction to injury is vasoconstriction
- Blood exposed to subendothelial layer activates platelets to adhere to the site
- Interaction is mediated by vWf
- Platelets are activated by releasing substances that recruit platelets to form a plug and maintain vasoconstriction
Coagulation cascade
- Coagulation factors are enzymes, cofactors, or substrates synthesized by the liver
- Calcium (factor IV) = required for most coagulation factors
- Vitamin K is essential for functional synthesis of factors II, VII, IX(9) and X
Extrinsic pathway
- initiated when tissue wall is damaged
- extravascular process because thromboplastin is not usually found in blood
- Tissue factor (thromboplastin), then binds with factor VII in plasma
- The combination activates factors IX and X initiating the common pathway
- End product is thrombin
- Thormbin
- initiates activity of other cofactors within the intrinsic pathway
- most potent platelet aggregation agent
Intrinsic pathway
- intrinsic factors found within vascular space
- Platelets release phospholipids allowing coagulation factors to activate each other
- Final product is fibrin - stabilises the temporary plug
Fibrinolysis
- Final stage of hemostasis
- once vessel is healed, plasminogen is activated
- plasmin breaks down the fibrin clot - which produces fibrin degradation products (FDP) and forms D-dimers
- FDP act as anticoagulants - inhibits the function of the platelets
Bleeding disorders of primary hemostasis
- related to platelets or vessels
- Vasculopathies results in: excessive fragility, or abnormally interactions with platelets
- Platelet disorders: quantitative (thrombocytopenia) or qualitative (thrombopathia)
What are the clinical signs of bleeding disorders of primary hemostasis?
- epistaxis
- petechiation
- ecchymosis
- gastrointestinal bleeding
- or prolonged bleeding from vessel or surgical site
- hematuria
- intraocular hemorrhage
Bleeding disorders of Secondary hemostasis
- Related to problems with coagulation cascade
- Acquired disorders: vit K antagonist rodenticide intoxication, drug side effects (heparin, colloids, Coumadin), DIC and liver disease
- Hereditary disorders: hemophilia and multiple factor deficiencies
Clinical signs of secondary hemolysis
- hematomas
- Hemoabdomen
- hemothorax
- hemoarthrosis
What diagnostic test would you use to detect primary hemostatic disorders?
- Platelet estimate (blood smear) and count (auto or manual)
- Buccal mucosal bleeding time (BMBT)
- Bone marrow evaluation
- Von Wilebrand factor assay
Platelet estimate and count
- blood smear and count manual or auto
- primary hemostasis test
- 1 platelet per oil immersion = 20,000 platelets
- 11-25 per high powered field normal
- large platelet indicates regenerative process
- machines can’t accurately count cat platelets due to size - use manual
- blood needs to be stored in EDTA
- assay should be done within 12 hours of sample collection
Buccal mucosal bleeding time (BMBT)
- detects primary hemostasis problem
- accurate with platelet counts of 50,000 - 100, 000uL as thrombocytopenia can cause a prolonged bleeding time
- if BMBT is prolonged with a normal platelet count = platelet dysfunction or a thrombocytopathia
- large margin of error - user dependent
Bone marrow evaluation
- assess megakaryocyte (platelet originates here) numbers
* Normal should have 3-5 megakaryocytes per HPF
Von Wilebrand factor assay
- performed by reference laboratories
* measures and reports amount of functional von Wilebrand factor
Diagnostic tests to detect secondary hemostatic disorders
- PCV and Total solids
- Observe clotting time in red top tube
- Coagulation panel, D-diners
- Intrinsic and Common pathways
a. Activated clotting times (ACT)
b. Activated partial thromboplastin time (aPTT)
5.Extrinsic and common pathways
A. Prothrombin Time (PT)
B. Protein induced by Vitamin K Antagonism or Absence (PIVKA)
At what age would you identify inherited coagulation defects?
At 6months of age or younger for severe cases.
Less severe cases become more apparent when they undergo their first surgical procedure.
What are the common ailments that should prompt you to consider hemostatic monitoring?
- Liver disease
- Biliary disease
- Neoplasia
- Significant trauma
- Certain toxin ingestion
- Patients with risk for disseminated intravascular coagulation
Thrombocytopenia
- most common primary hemostatic defect
- result from: decrease production, increased destruction, or increased consumption or sequestration
- significant thrombocytopenia (<40,000 uL): will start to show clinical signs of hemorrhage
- must rule out secondary hemostasis (DIC etc) first
Common causes of consumption or sequestration thrombocytopenia
DIC, sepsis, vasculitis, splenic torsion
What would you use to evaluate platelet production or rule in or out neoplasia, infectious, and immune mediated processes?
A bone marrow aspirate
Collecting blood sample for both coagulation and von Willebrand’s factor analysis
- Ensure blood comes into contact with citrate as soon as possible
- Jugular venipuncture using the vacutainer method is preferred
- don’t use this method if concern with coagulopathy
- central line and then other veins
- avoid traumatic venipuncture or incomplete blood draw
- may activate, deplete or dilute factors
- If plasma contains visible clots or is grossly hemolyzed - do not use sample
- These tubes should NOT be used for a coagulation panel or a von Willebrand factor assay:
- EDTA, heparin, serum separator, and clot activator
- Sample should be collected prior to giving plasma or cyroprecipitate therapy
- if not possible, collect sample no sooner than 48 hours post plasma or cryotherapy
- Blood MUST be centrifuged, separated, and frozen (if shipping) within 1/2 hour of being drawn
- if sample cannot be run immediately, separate plasma from RBCs and freeze plasma in separate clean plastic tube
- do not freeze whole blood
Buccal mucosal bleeding time procedure
- Restraint, sedate or anesthesia
- SQ recommended due to the possibility of impaired hemostasis
- Patient in lateral recumbency
- upper lip folded upwards and held in place with roll gauze which is tight enough to result in vessel congestion
- Standard incision made in the buccal mucosa with Simplate II device
- select an area without visible blood vessels
- start timing when trigger has been depressed
- remove device one second after triggering
- Blot the flow of blood at 5 second intervals with filter paper
- careful not to touch the edge of the wound
- record time to cessation of bleeding
- BMBT is the mean bleeding time for the two incisions
- if bleeding continues for >20mins, remove bandage and timing stopped
- Normal time to cessation of bleeding in dogs 1.7-4.2 mins with a mean of 2.6 minutes and cats 1.4-2.4minutes
What is the BMBT for dogs?
1.7-4.2 mins with a mean of 2.6mins
When should you remove the bandage for a BMBT procedure?
20 minutes
What is the BMBT for cats?
1.4-2.4mins
Immune mediated thrombocytopenia
- Common cause of decreased platelets is dogs
- affects middle age female dogs
- toy and old English sheep dogs overrepresented
What are the other causes of thrombocytopenia (non-immune mediated)?
Tick-borne disease, neoplasia, and heartworm disease
Definition of Thrombocytopathia
Dysfunctional platelets
Clinical signs of thrombocytopathia
- Primary hemostatic disorder
- Petechia (tiny spots)
- ecchymosis (bruises)
BUT platelets numbers are normal
*Confirmed with a prolonged BMBT
How is thrombocytopathia acquired?
- Frequently drug induced
- commonly seen in NSAIDs use
- Disease can precipitate platelet dysfunction
- pancreatitis
- hepatic disorders
- uremia
- various neoplasia condition
von Willebrand Disease (vWD)
*Inherited bleeding disorder seen in over 50 dog breeds
*Lack functional vW factor (vWf)
-necessary adhesive protein that promotes platelet adhesion and aggregation after vascular injury
*3 types:
TYPE ONE:
-seen in most other dogs
-Doberman Pinscher: low amount of vWf but protein itself has a normal structure
TYPE TWO:
-Most commonly seen in German shorthair pointers
-Low amount of vWf and an abnormal protein structure
-more severe
TYPE THREE:
-Most devastating form
-Scottish Terriers, Chesapeake Bay Retrievers, Shetland Sheep dogs
-circulating vWf is very low or absent!
- Low factor VIII
- binds to vWf to protect the Factor VIII from rapid breakdown in the bloodstream
What Factor is vWD patients deficient in?
Factor VIII
-binds to vWf for protection from rapid breakdown in the bloodstream
AT III
Inactivates thrombin with the goal to inhibit clot formation downstream from an injury
