Lab Evaluation of Hemostasis Part II

How many platelets/hpf are normal?

8-10

DDx for Thrombocytopenia

1. Rickettsial diseases (Ehrlichia, Anaplasma)(dx by serum titers)

2. Immune mediated thrombocytopenia (IMT)(dx by abs on platelets; exclude other causes)

3. Lack of marrow production(neoplasia, aplasia, fibrosis- BM aspirate!)

4. DIC(Coags, FDPs, blood smear)

Rickettsial dz- Anaplasma/Ehrlichia

Many sp. Ehrlichia (ewingii,canis..) & Anaplasma (phagocytophilum , platys) Others- RMSF

Petechiae or mucosal hemorrhages

Thrombocytopenia may be severe(<10,000 uL)

In the chronic form with E.canis →

pancytopenia

Immune mediated Thrombocytopenia can be caused by…

A) Rickettsial dz

B) History of drugs

C) Mostly idiopathic

D) Neoplasia

Immune Mediated Thrombocytopenia(IMTP/ITP)

Similar to IMHA- but antibodies are directed against platelets

Common cause of thrombocytopenia in dogs ; rare in other sp.

Idiopathic or secondary (drugs, tumors, rickettsial dz)

Dx of exclusion

DISSEMINATED INTRAVASCULAR COAGULATION(DIC)

Like severe inflammation

DIC- Thrombocytopenia

DIC- activation of widespread coagulation in the body → consumes coag factors and platelets → hypercoaguable

Widespread thrombosis throughout body at first; then hemorrhage because of depletion of platelets and coag factors (1’,2’)

Expected test results for DIC

Prolonged PT,PTT,ACT

Thrombocytopenia; 50-100k/ul

Increased FDPs/D-dimers(fibrin degradation products) Varies*

Blood smear: Schistocytes/keratocytes: Supports dx, absence does not exclude it

Decreased ATIII-Antithrombin III

Bone Marrow disease

Lack of bone marrow production → thrombocytopenia

Crowding out- Myelopthisis, can also be caused by myelofibrosis

Drugs-estrogen

Ehrlichiosis(damage stem cells in Bone Marrow)

Causes of bone marrow disease

Neoplasia of the bone marrow (leukemia,lymphoma)

Diagnostic test for bone marrow disease

Dx tests: Bone Marrow aspirate

vWd

Reported in many breeds of dogs. Cats & horses- but it’s rare

Doberman are the poster child (other include Shelties, German SHP, Scottish Terriers, mixed breeds)

Most common inherited disorder (diagnosed later in life)

3 forms (types I,II,III)

Expected test results for vWd

Performed if there’s an index of suspicion (breed, bleeding)

vWf assay – measures vWf in plasma

Will only bleed if [vWf]<30%

Platelet count will be normal (if the animal had severe blood loss, mildly decreased)

PT, PTT,D-dimers will be normal (this is a 1’ problem)

vWd

Decreased vWf = trait /carrier state (%)

70% and up = normal

50-69% grey area

x<50% @ risk of clinical dz

Platelet function defects inherited

Basset Hounds, Spitz- defect in IC signaling defect→px plt activation

Otterhounds, Great Pyrenees- defect in GPIIb/IIIa

Persian

Cattle: Simmental- IC signaling defect as above

Platelet function defects acquired

Hepatic/Renal failure, hyperproteinemia (>10mg/dL)

Drugs : Asprin & NSAIDs inhibit plt fn (COX inhibitors)

vwf

increases in pregnancy

Diseases of 2’ hemostasis

Vitamin K antagonism: The most common disease affecting 2’ hemostasis (coag proteins)

Liver failure: Reduced concentration of coagulation factors

DIC: Consumption of coag factors and platelets (both 1’& 2’)

Inherited defects: Hemophilia A (VIII) & B (IX) , C Factor XI

Oxidized Vitamin K needs to be reduced by an enzyme called Vitamin K epoxide reductase to…

become re-activated and act on other factors

Vitamin K epoxide reductase

Normally one vitamin K molecule is recycled many times by this enzyme and activates numerous coagulation factor molecules

Vitamin K antagonism

Vitamin K antagonists do not inhibit the action of reduced Vitamin K

Instead,

They inactivate the Vitamin K epoxide reductase enzyme that regenerates them

the concentration of active Vitamin K dependent factors will begin to decline depending on…

individual ½ life

Bleeding manifests when they drop to critical levels

Poisoning→ deficiencies in II,VII,IX,X

inactive forms continue to be produced →

build up

These inactive forms of II,VII,IX,X are referred to as ‘PIVKAS’(Protein Induced Vitamin K Antagonism)

Expected Results for vitamin K antagonist

Both PT,PTT are markedly prolonged

Factor VII has the shortest half-life so decreases first after poisoning

*If testing within 24-48 hrs PT may be prolonged before PTT

[Plt] usually normal, or mildly decreased if severe hemorrhage

[vWf] usually normal

D-dimers, usually normal; mild increase if cavitary bleeding with clots

clinical signs of vitamin K antagonism

Dyspnea (hemothorax, hemoabdomen)

Large hematomas at site of venipuncture

Causes of vitamin K antagonism

Rat poison (warfarin-like molecules)

Moldy sweet clover (cattle)

Severe cholestatic liver disease (Vit K factors are fat soluble; requires bile absorption from the gut)

Sulfaquinoxaline (coccidiostat)

How long will it take the animal with Vitamin K antagonism to respond to treatment?

Long enough to make new coagulation factors (days)

How do you know if you’ve treated long enough with Vitamin K for the toxin to clear?

Newer rodenticides have longer ½ lives- consider acute tx and re-test PT ~48 & 96 hrs after treatment stops

Liver failure

[Coag factors] by 2 mechanisms

Production or cholestasis(obstructed bile flow)→ fat absorption→ Vitamin K deficiency

Has to be severe liver disease ( Think icteric animals, high liver enzymes)

most animals will not bleed even with liver disease unless…

the procedure is invasive (liver biopsies)

Expected results of liver failure

Both PT,PTT could be prolonged

Platelet usually normal, or decreased depending on dz process

[vWf] usually normal

D-dimers- mild increase due to reduced clearance

Decreased production of urea, glucose, BUN

Increased ALP,ALT

Inherited defects doggie

All factors can be affected, Most commonly:

Factor VIII-Hemophilia A ** German Shepherds

Inherited defects cats

Factor XII- Cats

DIC

affects both primary and secondary

Inactive factors, produced by the liver require:

Vitamin K for carboxylation & activation

Active Vitamin K activates a coagulation factor →

Vit K molecule becomes oxidized and deactivated

The body has limited Vit K molecules all in the oxidized form → no more activation can occur so...

An animal ingesting Vitamin K antagonists initially has normal concentrations of fully activated factors, but no new factors can activate