Platelets Flashcards
Platelets
initial hemostatic plug
Temporary
Coagulation proteins
reinforce the platelets framework
Definitive hemostatic plug
Dog Platelet
cat platelet
horse platelet
cow platelet
Bird Platelet
Platelet Regulation by Thrombopoietin
- Major effect on every step of platelet production
- Produced predominantly by the liver at a constant rate
- Most TPO is removed by circulating platelets
- bound
- internalized
- degraded
- When platelet mass decreases, TPO concentrations increase
- Result is increased platelet production
- Inflammatory cytokines increased production
- reactive thrombocytosis
Thrombocytopenia
decreased platelet concentration
Thrombocytosis
increased platelet cocnentration
Thrombopathia
a qualitative disorder of platelets
Extrinsic Platelet Disorder
Platelets are normal
Von Willebrand factor missing or reduced
Intrinsic Platelet Disorder
Platelets are abnormal
Defective granules, membrane receoptors, signaling molecures, platelet formation protiens
Platelet disorder categories
- Congenital causes for abnormal concentration
- Acquired causes for abnormal concentration
- Congenital functional defects
- Acquired functional defects
Platelet-Type Bleeding
- Bleeding from mucosal surfaces, including:
- epistaxis
- Gingival bleeding
- Urinary tract hemorrhage
- GI bleeding
- Petechial and/or ecchymotic hemorrhage on any skin or mucosal surface
Normal Platelet Range
Roughly for most species:
100,000 to 500,000/uL
At what point might there be risk of spontaneous bleeding due to low platelet concentration?
<50,000 platelets/uL
Always evaluate a blood smear to confirm low platelet concentration
In platelet-type bleeding is occuring with platelet numbers at or above 50,000/uL, consider additional underlying problems:
Von Willebrand disease
Platelet inhibitory medications
Intrinsic platelet disorder
FelV induced platelet disorder
Hyperproteinemia
Neoplastic platelet disorder
Platelet Assessment
- Platelet concentration
- manual vs. automated counting
- Blood smear evaluation
- Mean platelet Volume (MPV)
- from automated
- Bleeding time
- Clot refraction
- Platelet Aggregation
- Molecular Assays
Automated Counting
Platelet clumping is probably the most common reason for erroneous platelet data
Manual Counts - hemocytometer
It is a common misconception that if there are clumps in the sample a manual platelet count will be more accurate than an automated count
NO NO NO
clumps affect the automated and manual count
Platelet Estimation from a bood film
VERY helpful
/ 1000x field for 10 fields
Some use Each platelet per 1000x field = 15,000 platelet/uL
Mean Platelet Volume (MPV)
An indication of the average size of circulating platelts
High MPV - with thrombocytopenia
Megakaryocytes are attempting to respond to the low platelet number by releasing larger platelets into the circulation
This is a favorable sign
But larger platelets are NOT younger platelets
Low MPV - with thrombocytopenia
may indicate insufficient numbers of megakaryocytes present or that they are failing to respond
Tests for Platelet Function
Buccal Mucosal Bleeding TIme (BMBT)
Clot Retraction - Test platelet function
Platelet Aggregometry - GOLD Standard
Buccal Mucosal Bleeding Time (BMBT)
- Indicator of primary hemostasis or platelet status
- Spring-loaded cassette delivers percise cut
- Avoids the hair and thick skin
- May require anesthesia
- Test reserved for patients adequate platelet concentrations but platelet function is questioned
- BMBT especially useful in doberman pinschers
- BMBT cannot be used to detect coagulopathies
- hemophiliacs have normal buccal mucosa bleeding times
- Dog: 1.5-4 mins
- Cat: 1-2.5 mins
Clot retraction - Tests platelet function
- Draw 0.5mls blood directly into plastic syringe contianing 4.5mls of cold saline
- Mix gently
- Dispense 2 mls of the mixture inot each of 2 glass tubes containing 0.1ml to 10 units/ml thrombin
- Cap and mix the tubes. Place the tubes in a refrigerator for 30 minutes
- Transfer tubes to a 37C water bath
- Record the degree of clot retraction at 1 and 2 hours as 1+ to 4+
Platelet Aggregometry
GOLD STANDARD
the definitive means for evaluating platelet function
Highly specialized and not readily available
Testing must be completed within 4 hours of collection
Platelets are stirred in front of a light source in a siliconized glass cuvette.
Various agents are added to the cuvette and the ability of the platelets to respond is recorded on a strip chart recorder
Cats and their Platelets
- ~10 times more reactive than other species
- Highly variable in size
- Giant platelets are a common finding
- Impedance hematology analyzers do not give accurate platelet concentrations
- Cats with thrombocytopenia and bleeding usually have another underlying problem
- Cats with FeLV infection may have any combination of platelet concentration and clinical signs
Congenital Thrombocytopenia:
Inherited Macrothrombocytopenia
- Affects >90% of Cavalier King Charles Spaniels in US
- carrier of affected
- Affected do NOT have clinical bleeding
- Platelets between 30,000 and 100,000/uL
- Heterozygotes have platelets concentrations between homozygote and unaffected
- Mutation is the gene encoding beta 1-Tubulin
- Identical or similar mutaions identified in other breeds
- English toy spaniels, Shih tzu, matlese, jack russel terrier, havanese, toy poodles, boxer, cocker spaniels, bichon frise, miniature schnauzer, komondor, chihuahua, labrador retriever, norfolk and cairn terriers, and several crossbreed dogs
- Misdiagnosis can lead ot inappropriate treatment with steroids and or antibiotics
Acquired Thrombocytopenia: Causes
- Immune-mediated
- Drug-induced
- Enhanced consumption
- Virus-induced
- Decreased production
- Sequestration
Immune-mediated Thrombocytopenia
Circulating platelts and/or megakaryocytes are destroyed by immune-mediated mechanisms:
Platelets concentration is usually very low
Confirmed by blood smear evaluation
Immune-mediated Thrombocytopenia:
Causes
- Primary or autoimmune
- Secondary to immune-complex absorption or neoantigen expression
- Incompatible transfusion
Rickettsial-Induced Thrombocytopenia
- Ehrlichia Canis
- Anaplasma platys
- Anaplasma Phagocytophilum
- Rickettsia rickettsia (Rocky mountain spotted fever)
Immune mediated clearance
Decreased life-span
Vasculitis-induced consumption
Drug induced thrombocytopenia:
Primary
circulating platelets are destroyed by drug interaction
Drug Induced thrombocytopenia:
Secondary
Drug-Dependent vs. Independent
Drug induced thrombocytopenia:
Secondary (Bone marrow suppression)
Estrogen; antifungals; anticancer drugs; antibiotics; antivirals; and anti-inflammatory drugs
Disseminated Intravascular Coagulation (DIC)
Pathological process characterized by the widespread activation of the clotting cascade that results in the formation of blood clots throughout the body
Can occur secondary to any event that causes massive tissue damage:
Septicemia
Neoplasia
Parasites
Vasculitis
Viruses
Destruction or crowding of the marrow cavity resulting in generalized marrow hypoplasia
Myelophthsis/myelofibrosis
Myeloproliferative disease
Inflammatory disease
Congenital Extrinsic Platelet Function DIsorders:
Von Willebrand Disease
- most common inherited bleeding disorder in dogs, rare in cats, cattle, rabbits, pigs, and horses. Pigs are a common disease model
- An extrinsic platelet function disorder
- persentation is like taht of thrombocytopenia, however, platelet concentration is normal
- Von Willebrand Factor is markedly reduced
- decreased platelet adhesion
- Diagnosed using ELISA to determin antigen levels
- ALWAYS USE PLASMA< NOT SERUM
- DNA-based testing available for some breeds
- Clot retraction test is normal
- APTT is normal
- An extrinsic platelet function disorder
Von Willebrand Disease
Type 1
Quantitative disorder
Von Willebrand Factor is detectable but low
Most common form of Von Willebrand Disease in Dogs
Very common in Doberman Pinschers
Von Willebrand Disease:
Type 2
Qualitative disorder
Von Willebrand Factor multimers are altered
Less common in domestic species
Von Willebrand Disease:
Type 3
Quantitative Disorder
Von willebrand factor is not detectable
Rare in dogs
Scotties, Shelties,, Chesapeake Bay Retriever
Von Willebrand Disease
Manifestations
Prolonged bleeding at tail docking, ear cropping, or dew claw removal, spay/neuter are common
+/- mucosal bleeding primarily manifested by gingival bleeding, epistaxis, and hematuria
Many dogs that carry this disease in thier genetic makeup go undetected until a minor surgery or small, superficial injury results in significant blood loss
Testing for Von Willebrands Disease
- vWF antigen:
- EDTA or cirtrated Plasma
- do NOT let the sample clot
- Clotting will result in vWF incorporated into clot
- DNA test
Congenital Intrinsic Platelet Function Disorders:
- Glanzmazz thrombasthenia
- CALDAG-GEFI thrombopathias
- basset hound thrombopathia
- Spitz thrombopathia
- Landseer-ECT thrombopathia
- Bovine Thrombopathia
- P2Y12 ADP receptor defect
- LAD-III syndrome
- Cycline Hematopoiesis
- CHediak-Higashi syndrome
- Dense Granule Defect
- Scott syndrome
Glanzmann thromboasthenia
Inherited disorder described in otterhounds, Great pyrenees, and horses
Clot retraction is absent
Clinical Signs:
Platelets type bleeding
Chronic epistaxis, gingival bleeding
CalDAG-GEFI thrombopathia
Mutations in the gene encoding calcium diacylglycerol regulated quanine nucleotide exchange factor 1 resulting in signal transduction abnormalitity
DNA testing available at Auburn University
- Clinical Signs:
- epistaxis, gingival bleeding, petechiation, hematuria, excessive bleeding with minor procedures
- Platelet, vWF, coagulation screening assays – normal
- Defect of signal transduction resulting in decreased binding of platelets to fibrinogen
- Thrombin-induced aggregation – extent normal, but rare impaired. Clot retraction – normal
Inherited Platelet Function Defects:
Chediak-Higashi Syndrome
autosomal recessive
Abnormal leukocyte, melanocyte, and platelet granulation
Platelets do not form tight aggregates in response to ADP
Prolonged bleeding at incision sites, and the development of hematomas following venipuncture
Inherited Platelet Function Defects:
Cyclic Hematopoiesis
Autosomal recessive grey collies
Cyclic fluctuations in neutrophils, reticulocytes, and platelets
Neutropenic episodes occurring approximately every 12 days
Mortality is high, most puppies die prior to 6 months of age due to fulminating infections
Platelet numbers usually do not decline below the normal range and fluctuate between 300,000 and 700,000/uL
Platelet reactivity is defective
Platelet dense granules are absent
Clot retraction and platelet adhesiveness are impaired
P2Y12 mutation
~60% of the dogs tested are wither Carriers or Affected for the mutation
The gene pool is small, prevalence is likely high, be careful
Carriers have been reported to have clinical signs
Clinical signs of bleeding in affected or carrier dogs are not recognized unless they are challenged with significant trauma or surgery
Most common reports have described severe bleeding following routine spays/castrations; many die
Scott syndrome
When platelets become activated they express a negatively charged surface due to the flip-flop of negatively charged phosphatidyl serine
Negatie surface required for assembly of coagulation factors
A platelet disorder wiht clinical signs more typical of a coagulopathy
German Shepherd Dogs
Rare
Summary:
Extrinsic Disorders
Platelets are normal.
A protein necessary for platelet function is either absent, reduced, or dysfunctional.
Summary:
Intrinsic Disorders
Platelets are abnormal
Abnormalities may be related to granules, membrane glycoproteins, signal transduction proteins
Summary:
Inherited Thrombocytopenia
Seen in cavalier king charles spaniels and other breeds
Does not result in clinical bleeding
NO TREATMENT NECESSARY
Acquired Qualitative Platelet Function DIsorders
Feline Leukemia Virus
Viral accumulation in cytoplasm of megakaryocytes resutls in infection of platelets
Thrombocytopenia, thrombocytosis or function defects may result
Acquired Qualitative Platelet Function Disorder
Drug Induced
Drugs can impair platelet funciton by inhibiting receptor binding agonists, by inhibiting transduction of messages or by inhibitinng response
Drug-induced impairment is usually not clinically significant unless coupled with another underlying disorder or the patient requires surgery
