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complex process that stops bleeding, forms stable clot then breaks down clot.
stays where it's put
Three steps of hemostasis
- primary hemostasis: (platelet activation, adhesion and aggregation)
- Secondary hemostasis: cascade of enzyme conversions leading to stable clot
- Finbrinolysis: breakdown of fibrin clot, activated simultaneously with hemostasis
Simple order of blood clotting
- blood vessel injury, vasoconstriction, release of collagen
- circulating platelets adhere to damage and collagen, form plug (Von Willebrand)
- Platelets release chemicals activating blood clotting factors
- cross-linked fibrin clot formed in clotting cascade
- damage to tissue activates
- Factor 7 (tissue thromboplastin)
- Activates Intrinsic pathway
only non-protein clotting factor
- tissue thromboplastin
- in extrinsic pathway only.
Clotting factors are primarily produced by
- activated by extrinsic.
- damage to blood vessel, wet, anionic surface.
- Factors 12, 11, 9, 8 (kmart special)
- 10, 5, 2, 1, 8
- activated by both extrinsic and intrinsic
- 10a activates 5a, activates 2 (prothrombin into thrombin), activates 1 (fibrinogen into fibrin), stabilizes clot. 8 turns fibrin into clot, prolongs von willebrand's
- fragments of megakaryocytes, makes platelets.
- 200,000 - 500,000 for most species, 100,000 is thrombocytopenia, <50,000 signs of hemmorrhage
- 30-40% in spleen.
- Birds and reptiles have nucleated platelets.
precursor to thrombocytes
- forms hemostatic plug
- initiates clotting cascade
- initiates clot retraction
- constrict blood vessels
- phagocytize some particles, particularly damaged cell membrane.
EDTA tube, used to check platelets
citrate. Used to check clotting factors
used to check fibrin split products
Whole blood clotting time test
- Checks intrinsic and common (12, 11, 10, 9, 8, 5, 2, 1)
- Dogs: 2-10 minutes
- Cats: 8 minutes
- Horses: 4-15 minutes
- Cattle: 10-15 minutes
Buccal mucosa bleeding time test
- Detect abnormalities in platelet function and von Willebrands
- usually 1-5 minutes.
- Long indicates thrombocytopenia (usually already know), platelet dysfunction, vWF deficiency
pinpoint bruising on gums/pinna. Look at CBC, if normal do buccal mucosa bleeding time test
Three methods for calculating platelet numbers
- platelet estimate (peripheral blood smear)
- platelet manual count (hemocytometer, within 5 h)
- Platelet automated count (automated cell counter, trouble with overlap with RBC and clumping)
Peripheral blood smear in platelet evaluation
- examine monolayer in blood smear, count min 10 microscopic fields
- d/c/cw 8-10 platelets per field min
- horse 5 platelets per field min
- each platelet = 15,000-20,000 platelet/uL
- average # x 15,000
- morphology (young are macro, increased production)
- cats have larger platelets
- nonactivated have granules, activated may or may not.
Clot retraction test
- Evaluates plately number and function in intrinsic and extrinsic.
- Checks platelet function (don't use if on aspirin)
- depends on interaction between platelet receptors, thrombin, fibrinogen.
- 1-2 hours for good clot retraction
abnormal platelet function
blotches and bruises on gums, can be pinna as well. Indicates low platelets.
thrombocytopenia, abnormal platelet distribution
splenomegaly, hypothermia (liver)
thrombocytopenia, decreased platelet production
drugs, chemo, infections, irradiation, marrow replacement
thrombocytopenia, decreased platelet survival
- immunologic (IMT)
- non-immunologic (blood loss, DIC, localized intravascular coagulation, vasculitis (leaky vessels), drugs, envenomation, rodenticide)
- usually no clinical signs.
- iron deficiency anemia (non-regenerative anemia, microcytic, hypochromic)
- inflammatory conditions
- epinephrine release (fear or pain)
- myeloproliferative disorders
- platelets aren't low, just not working.
- Consider with prolonged bleeding time or clot retraction.
- Can be hereditary or acquired.
- drug exposure (NSAIDs, antihistamines, iso, phenylbutazone in horses), envenomation, hepatic disease, increased fibrin degredation products, immune mediated, Infectious (FeLV), renal failure, neoplasia
Fibrinogen/plasma test for coagulation evaluation
- measure protein on refractometer (100mg-500mg/dL)
- decreased: liver disease, congenital or factors used up. Hemolysis and lipemia falsely used up.
- increased: inflammation, hyperadrenocorticism, pregnancy, nephrotic syndrome in dogs (proteinuria, hypoalbuminemia, hypercholesteralemia, edema)
- DIC: can be any reading of platelets.
Activated clotting time test for coaguation
- ACT. Evaluates intrinsic and common (all factors but 7), not very sensitive. 90-95% problem to detect
- Blood into tube with diatomaceous earth, 37 degrees, check for clot time.
- horses<190 sec
- cattle<180 sec
- cats< 75 sec
- dogs<100 sec
Activated Partial Thromboplastin time (APTT)
- tests intrinsic and common pathways.
- blue top, 9:1 blood to citrate, centrifuge within 60 minutes, keep refrigerated. Analyze within 2 hours or freeze.
- 8-13 sec in dog, <30% normal control.
- Indicates trouble in factors, substitute known deficiency factors and see if corrects.
- check for liver disease, vitK deficiency, drug overdose, toxins and DIC
Prothrombin time (PT) or one stage PT (OSPT)
- evaluates extrinsic and common.
- citrate tube (9:1), treat sample like PTT.
- normal is 6-8 sec in dog, <30% longer than normal control.
- indicates deficiency of factors in extrinsic (7) or common (10, 5, 2,1)
- liver disease
- Rodenticide affects #7 (most common)
After ingestion of rodenticide, ______________ will show up first.
- Factor VII deficiency (extrinsic pathway, PT) because it has the shortest half-life. Eventually all pathways will be effected (2,7,9,10).
- Early rodenticide = normal PTT, ACT
- Protein Induced (Invoked) by Vitamin K Absence. Thrombotest.
- Looks for built-up precurser proteins not used because of vit. K deficiency. (Pre-2, Pre-7, Pre-9, Pre-10)
- rarely run, not better than PT for rodenticide. Good for subtle extrinsic/common disorders.
D-Dimer and Fibrin degradation products
- formed when a clot is degraded, evidence of fibrolysis.
- Used to find DIC and thromboembolism in all but horses.
- d-dimer better than FDP for fibrinolysis (not DIC or TE)
Thrombocytopenia presents in the lab with
- decreased platelets
- normal PT
- normal PTT
- variable ACT
- abnormal clot retraction
- prolonged BMBT.
- most common coagulopathy.
- Caused by bone marrow damage, infections, immune, abnormal distribution, low production/survival, hemodilution
thrombocytopathia presents in the lab with
- normal platelet count
- normal PT
- normal PTT
- normal ACT
- Prolonged BMBT
- abnormal clot retraction.
- abnormal platelet function.
- Congenital or acquired through drugs (Aspirin), renal failure, increased FDPs (fibrinolysis, DIC), envenomation, hepatic disease, immune, infection, neoplasia.
Intrinsic pathway coaguation defect lab findings
- normal platelets
- normal PT
- prolonged PTT
- Prolonged ACT
Intrinsic pathway coagulation defect diseases
- Hemophilia A
- hemophilia B
- von Willebrand's Disease
- Most common intrinsic pathway defect.
- Factor 8 deficiency
- Severe hemorrhage and ecchymoses
- sex-linked recessive--males in any breed
- intrinsic pathway defect
- factor 9 deficiency
- mild to severe bleeding
- sex-linked recessive--males in any dog and DSH cats (siamese)
von Willebrand Disease
- Most common hereditary bleeding disorder in dogs (dobermans), rare in others.
- Missing or ineffective von Willebrand factor, which decreases factor VIII and makes platelets not adhere.
Clinical signs of von Willebrand
- mild to severe mucosal hemorrhages
- cutaneous bruising
- prolonged hemorrhage from trauma/surgery (tail docking, tooth extraction, dewclaw removal, blood extraction)
- Hemoarthrosis and hematomas in horses
von Willebrand lab results
- prolonged BMBT without thrombocytopenia
- normal PT
- normal or mildly prolonged PTT
- von Willebrand antigen test (ELISA) uses anti-vWF antibodies as a % of control. 50% is positive, 70% is negative (between unclassified)
enzyme linked immuno-sorbant assay
Causes of prolonged PT, normal everything else
- Factor VII deficiency (bruising not bleeding)
- early hepatic disease (eventually more problems)
- early vit K deficiency/antagonism/absense (Warfarin toxicity), will eventually effect all.
Common pathway lab findings
- prolonged PT
- prolonged PTT
- prolonged ACT
- normal platelets
Vitamin K antagonism or deficiency
- will effect II, VII, IX, X
- effects VII first, shortest half-life
- bleeding is common (can present as breathing problems) 3-7 days after exposure
- Can come from warfarin or rodenticides
- Therapeutic coumadins
- sweet clover or sweet vernal grass (large animals)
Vitamin K deficiency, not warfarin
- rarely causes hemorrhage
- vitK absorbed in intestine, produced/ingested by intestinal bacteria
- Caused by serious, prolonged anorexia, malabsorption of vitamin K (fat-soluble, so no-fat diet)
Liver disease as common pathway deficiency
- Liver makes I, II, V, VII, VIII, IX, X, XI, XII
- very severe liver disease causes hemorrhage
DIC stands for
disseminated intravascular Coagulation
DIC caused by
- LOTS of things. Thromboplastin in tissue exposed, sets off clotting cascade.
- Septicemia, viremia, parasites, tissue injury, intravascular hemolysis, obstetric complications, malignancy, shock, liver disease, pancreaitis, GDV, abomasal displacement, toxins
- starts as hypercoagulation due to activation of clotting cascades (not evident clinically)
- multiple small clots form in vessels, consuming platelets and clotting factors
- Fibrinolysis, leaving d-dimers and fibrin split products
- fibrin split products (FDPs) are anticoagulants.
- Severe hemorrhage
DIC lab abnormalities
- decreased platelets (first sign, prolonged BMBT)
- Prolonged PT
- Prolonged PTT
- Prolonged ACT
- Decreased fibrinogen
- increased FDP or d-dimers