Haematology and Immunology: Clinical COPY Flashcards
What type of immune response is immune mediated disease generally caused by?
TH2 responses (antibodies against a self antigen)
What percentage of dogs will have bacteria when on immunosuppressive treatment?
30%
Why is PT often prolonged first in disorders of coagulation?
Factor VII from the extrinsic pathway has the shortest half life of all the factors so is often consumed first.
Prothrombin time:
- Test characteristics
- What it tests
- Point at which the test is considered complete
- Plasma is added to a medium containing calcium chloride and tissue factor within a lipid membrane.
- Tests the extrinsic and final common pathway
- The PT finishes when fibrin strands form
aPTT
- Test characteristics
- What it tests, what it does not test
- Plasma is incubated with a contact activator (e.g. kaolin, celite) which will activate XII and the pathway continues.
- Tests the intrinsic pathway and final common pathway.
- The fibrin stabilising complex (XIII) and the extrinsic pathway (VII) are not tested.
What Ddx could you have for:
- Increased PT but normal aPTT?
- normal PT but increased aPTT?
- Early rodenticide toxicity
- Factor XII (Hageman) deficiency, Factor XI (haemophilia C), Factor IX (Haemophilia B) or Factor VIII (Haemophilia A), heparin therapy.
ACT
- Test characteristics
Whole blood is used and a contact activator is added. The platelets acts as their own membrane for the tests. Therefore, visible clot formation is the end point.
How is fibrinogen measured?
The Clauss method: fibrinogen is exposed to a large amount of thrombin.
Reasons for reduced fibrinogen concentrations
Anticoagulant use
Elevated FDPs
Decreased albumin
XIII deficiency (as the fibrin is not stabilised)
Amyloidosis
How is thrombin clot time measured?
By adding lots of thrombin to citrated plasma. It is measuring the function/levels of fibrinogen.
What is FDP measurement testing and what are some Ddx if this is normal?
FDPs are produced when plasmin lyses fibrin clots. Therefore, elevations may occur in:
- DIC
- Rodenticide toxicity
- Hepatic disease
- Thrombotic diseases
What are D-dimers?
These are specific FDPs that are only produced from cross-linked fibrin. They have a very short T1/2 so can indicate recent fibrinolysis.
TEG parameters and alterations with hyper and hypocoaguable states.
R = the time to onset of fibrin formation
K = time for the deviation of the needle by 20mm (this is a measure of speed of clot formation)
alpha angle = speed of clot formation
MA = maximum strength of the clot
The LA30 and LA60 = the amount (%) of clot that has undergone lysis by 30 minutes and 60 minutes, respectively.
Which TEG parameters indicate:
- Coagulation factors
- Platelet number and function
- This is generally indicated by the reaction time (time to fibrin formation)
- This is indicated more by the rate of fibrin formation (e.g. alpha angle, k etc.)
How much of a reduction in clotting factor activity is required before PT/aPTT are prolonged?
50-70%
What will the following alterations result in on TEG testing?
a) low PCV
b) Increased fibrinogen
c) Thrombocytopenia
a) + b) will appear hypercoaguable
c) will appear hypocoaguable
What percentage of mortality in IMHA is likely due to thromboembolic disease?
up to 50%
What is the incidence and survival of ATE in cats with cardiac disease?
33% incidence and 35% survival
What percentage of dogs with PLN will suffer thromboembolic complications?
14-27%
What is the most common cause of pulmonary thromboembolism in dogs?
Neoplasia
In what neoplasias is DIC a common problem?
Haemangiosarcoma
Mammary carcinoma
Pulmonary adenocarcinoma
How long does it typically take for clinical bleeding to occur following rodenticide toxicity?
2-5 days
What are PIVKAs
Proteins induced by vitamin K abscence. This test will be prolonged if vitamin K is deficient in some way.
Which factor is increased in DIC and is thought to be a major contributor to its development?
Increased expression of tissue factor.
The extrinsic pathway is then activated and there is consumption of coagulation factors. Therefore, there are two phases:
- Compensated = hypercoaguable
- Uncompensated = bleeding
What are the diagnostic criteria for DIC?
n.b. there may be some actual criteria here but this is what I have noted from Ettinger
PT/aPTT alterations
Thrombocytopenia
Increased FDPs/D-dimers
Hypofibrinogenaemia
Decreased antithrombin
Treatment of DIC
Compensated phase = anticoagulants
Uncompensated = FFP transfusion
What are acquired anti-coagulants?
Spontaneous development of antibodies to a coagulation factor, anti-phospholipid antibodies (lupus anticoagulant) is another type.
How are acquired anti-coagulants tested for?
By the ‘plasma mixing test’ which is where patient and control plasma is mixed. Coags would remain prolonged following mixing due to the presence of antibody in the patients plasma.
Which clotting factors are contained in the following blood products:
- FFP
- Cryoprecipitate
- Cryosupernatent
- Stored plasma
- FFP = contains all the factors
- Cryoprecipitate is primarily VIII, XIII, vWF, fibrinogen and fibronectin (less than FFP but small volume required)
- Sufficient coagulation factors other than those in cryoprecipitate
- Lowe levels of V and VIII but has adequate VitK dependent factors.
Which blood products should be used for rodenticide toxicity?
FFP or stored plasma are best for this.
Pathophysiologic and genetic basis for Scott syndrome
Diagnosis
Deficient procoagulant activity (phosphatidylserine) on the platelet surface.
Autosomal recessive trait of GSD
Diagnosis:
- Prothrombin consumption assay
- Flow cytometry for the PTS on the platelet surface
What breed of cat has vitamin K gamma-glutamyl carboxylase deficiency been documented in?
Devon-Rex
Which factors are deficient in the following diseases?
- Haemophilia C
- Haemophilia A
- Haemophilia B
- Stuart-powell deficiency
- Christmas disease
C = XI
B = IX (aka. christmas disesase)
A = VIII
- X
What is the mode of inheritance of haemophilia A & B?
Autosomal X-linked recessive.
What factor can potentially be increased with desmopressin therapy?
Factor VIII is increased in people but not dogs.
If haemorrhage is suspected in a cat with Hageman’s trait, what should be evaluated for next?
A concurrent haemophilia as Hageman trait should not result in clinical bleeding.