Haematology and immune mediated disease Flashcards
What is the difference between petechiae and ecchymoses?
Petechiae - <3mm, capillary bleeding
Ecchymoses - larger, small arteriole bleeding
Causes of thrombocytopenia
Increased destruction, consumption, sequestration
Reduced production
Coagulation abnormalities in DIC
Initially hypercoagulable, progresses to consumptive coagulopathy
Causes of increased platelet consumption
DIC
Causes of platelet sequestration
Hepatomegaly, splenomegaly, hypotension, hypothermia, endotoxaemia
Name some inherited thrombopathias and the breed association
Glanzmann’s - Great Pyrenees/Otter Hounds
Thrombopathia of Bassett Hounds and Spitz
Delta storage pool deficiency - American Cocker Spaniel
Causes of acquired thrombopathias
Infectious - rickettsial
Hepatic disease/uraemia
Neoplasia
Drugs - aspirin/clopidogrel, carprofen, hydroxylethyl starch solutions, omega-3 FA (in vitro only)
Likely cause of surface bleeding in patient with normal platelet number and function
Vascular disorder
Vascular disorders
Primary immune-mediated
Secondary to medications, infections, neoplasia
Normal BMBT (dogs and cats)
<4 mins (dogs)
<2 mins (cats)
Clinical signs of primary haemostat disorder
Petechiation, ecchymoses, mucosal bleeding, ocular haemorrhage, haematoma formation
Calculation for manual platelet count
Platelets/hpf x 15-20
What haematology findings are suggestive of increased platelet production?
Increased MPV, PDW, reticulated platelets
What is the general pathogenesis of most immune-mediated haematological diseases (Th-1/Th-2)
Th-2 (antibody-mediated)
What are the mechanisms through which immunosuppressive medication act to reduce immune-mediated disease?
1 - reduced production of antibody by lymphocytes
2 - suppressing clearance of opsonised cells by macrophages or complement
Which antibody class is most associated with IMHA? What is it's half-life?
IgG
7 days
How can platelet function be assessed?
Impedance whole blood aggregometry
Plasma-based light transmission aggregometry
Platelet function analysed (PFA-100)
Which PFA cartridge has the highest sensitivity for canine platelets?
Collagen/ADP
What is assessed by platelet aggregation?
Platelet number
Platelet function
vWF
Which pathway and factors are assessed by PT?
Extrinsic
FVII, X, V, II, I
What does an elevated PT with a normal aPTT indicate?
FVII deficiency
What pathways and factors are assessed by aPTT?
Contact pathway, intrinsic pathway, common pathway
Prekallikrein, FXII, FXI, FVIII, FIX, FX, FV, FII, FI
Which factors do not affect aPTT?
FVII and FXIII
Are PT/aPTT affected by heparin?
PT - no
aPTT - yes
What is a common clinically irrelevant incidental finding on coagulation testing in cats
Factor XII deficiency (prolonged aPTT, normal PT)
What conditions are associated with an elevated aPTT but normal PT?
Haemophilia (A, B, C), heparin, FXII def
What conditions are associated with elevated PT and aPTT?
Rodenticide toxicity, liver disease, DIC, hypo-/dysfibrinogenaemia
What is tested by the ACT?
All factors but VII and XIII
What are FDPs?
What does an elevation suggest?
Created when plasmin lyses fibrinogen, fibrin monomers, insoluble fibrin, cross-linked fibrin
Plasmin activity
What are D-dimers?
What does their elevation indicate?
What is their half life?
Form of FDP generated from cross-linked fibrin
Thrombin generation, fibrin formation, cross linking by FXIIIs and plasmin activity
Short half life (5h) - indicate recent fibrinolysis
How does altered PCV affect TEG analysis?
Higher hct - hypo coagulable tracing
Lower hct - hyper coagulable tracing
What is assessed by a calibrated automated thrombogram (CAT)?
The ability to generate thrombin in real time in-vitro in response to a specific stimulus
Used with platelet-poor or platelet-rich plasma
Virchow’s triad
Vascular stasis
Increased coagulability
Disruption or activation of vascular endothelium
By how much does a clotting factor need to be reduced to elevate PT/aPTT
30-50%
List acquired hyper coagulable states
IMHA Cardiac disease (HCM, endocarditis, dirofilaria) PLE PLN Neoplasia Endocrine dz (HAC, hypoT, DM) Prednisolone Inflammation/Sepsis
List acquired hypo coagulable states
Vit K deficiency - rodenticide
Hepatic failure
DIC
Factor VIII and IX inhibitory antibodies as consequence of multiple transfusions in haemophilia
Vit K dependent coagulation factors?
II, VII, IX, X
Protein C+S
How to anticoagulant rodenticides cause bleeding?
Inhibit vitK epoxide reductase - reduced vita essential for carboxylation of glutamic acid residues on coagulation factors
How soon after rodenticide ingestion is bleeding typically observed?
2-5 days
What can be measured to indicate rodenticide ingestion?
PIVKA - elevates within 12 hours of ingestion
What is the primary mediator of DIC?
Tissue factor
What are the risk factors for DIC development?
Prolonged hypotension
SIRS
Disturbed blood flow to major organ
Major tissue trauma
What has been associated with Increased mortality in dogs with DIC?
High D-dimer, low antithrombin, hypo coagulable TEG trace
Are the following indicated in DIC;
- Heparin
- Plasma
Heparin - no
Plasma - if active bleeding