Everything on Platelets and Granulocytes Flashcards
What is the MVP?
Mean platelet volume
Avg is 8-12 fL
An increase in MVP is assoc. with immature PLT’s
What is the IPF?
A marker of thrombopoietic activity
Detects RNA in immature platelets
What is platelet aggrogemetry?
Platelet Rich Plasma (PRP) is prepared and warmed to 37C. An agonist is added (ADP, epinephrine, collagen, ristocetin, or arachidonic acid) which should cause plt to aggregate and change the optical density.
This change is recorded in a graph and interpreted to identify the qualitative platelet disorder
What is the PFA-100?
Uses whole blood at a high shear rate
Blood is aspirated through a capillary with a membrane coated with an agonist.
Sensor detects the formation of a platelet plug
What is the clot retraction test?
Blood is added to a glass tube in at 37C water bath for 1-3 hrs. A normal clot should retract with in 30-60 min.
No retraction could indicate Glanzmann’s thrombasthenia
What antigens are on platelets?
ABO - Both intristic and adsorbed onto membrane
Lea , Leb, Ii, P, Pk
HLA Class I
Human Platelet Antigens
What is a minor platelet incompatibility?
Donor plasma ABO incompatible with recipient red cells
What is a major platelet incompatibility?
Donor platelets are incompatible with recipients plasma
What HPA are found on glycoprotein IIIa
HPA-1a/b and HPA-4a/b
HPA-1a 98% of Caucasians (most common antibody)
HPA-1b 27% of Caucasions (2% are homozygous)
Glanzmann’s thrombasthenia Type I, a disorder of platelet function, lack glycoprotein IIIa
What is Phase I for testing for Platelet Specific Antigens and Antibodies?
Mixing patient serum with normal platelets and using platelet function-dependent endpoints such as
- Platelet aggregation/inhibition of platelet aggregation
- Inhibition of clot retraction
- Inhibition of platelet migration
- Complement fixation
- Platelet Factor 3 release
What is Phase II for testing for Platelet Specific Antigens and Antibodies?
Phase II assays can be used to detect platelet antibodies as well as for crossmatching. The SPRCA assay (solid phase red cell adherence) is the most widely used of the Phase II assays. Chloroquine has been shown to disrupt the HLA Class I antigens found on the platelets. This makes it easier to determine if there are antibodies to platelet antigens or if there is just antibodies to Class I HLA antigens.
Can also use Flow cytometry or Radioimmunoassay
What is Phase III for testing for Platelet Specific Antigens and Antibodies?
detect platelet antigen by specific MoAbs
Monoclonal antibody immobilization of platelet antigens (MAIPA)
Antigen capture ELISA (ACE)
Modified antigen capture ELISA (MACE)
Immunobead assay
How does Solid Phase platelet testing work?
Intact platelets are immobilized on round-bottom wells of microtiter plates and then sensitized with the antibody to be detected. After washing off the excess serum, red cells coated with an antibody specific for human immunoglobulins (indicator cells) are added. The tray is then spun and examined visually; if antibody is bound to the platelets, the indicator cells will be distributed evenly over the bottom of the well like a “carpet”; if no antibody is present, the indicator cells have nothing to “stick” to and a red cell pellet forms in the center of the well. A limitation of the SPRCA assay is that is unable to distinguish platelet specific antibodies from HLA or ABO antibodies. An example of a SPRCA assay that is commercially available for platelet crossmatching is Immucor Capture-P. Using whole platelets can detect antibodies that are missed by MACE because antigen is destroyed
What criteria is used to determine if a patient is refractory to platelets?
CCI <7500 at 1 hour
CCI <5000 at 20 hours
What are non-immune causes of platelet refractoriness?
Massive bleeding (consumption) Fever Sepsis Splenomegaly (splenic sequestration) DIC Effects of drugs TTP (thrombotic thrombocytopenia purpura
What are immune causes of platelet refractoriness?
HLA antibodies : most common cause!!
Platelet specific antibodies: anti-HPA-1a most frequently identified platelet specific antibody
ABO antibodies; some times overlooked as a cause!
What are acquired disorders of platelets?
Heparin or asprin
Mechanical bypass - PLT’s are activated after contact with bypass machine
Uremia
What are congenital disorders of platelets?
VonWillebrand disease (Not a platelet problem)
Bernard-Soulier
Glazmann’s thrombathenia
What is ITP?
ITP is a disorder of accelerated platelet destruction; this destruction is mediated by platelet autoantibodies, with removal of the platelets occurring in the spleen. Acute ITP is mainly seen in children with an abrupt onset of severe thrombocytopenia and bleeding, often after a viral infection. Chronic ITP is most often a disease of adults and affects twice as many females as males. Treatment consists of steroids, high dose IVIG, Rh immunoglobulin (RhIg), and splenectomy as a last result. Platelet transfusions not effective.
What is NAIT?
NAIT stands for neonatal alloimmune thrombocytopenia. Antibodies in maternal plasma (either platelet specific antibodies or HLA antibodies) cross the placenta and destroy the infant’s platelets. Immunization of the mother occurs as frequently in the first pregnancy as subsequent, so no way to predict NAIT. Mother is usually the platelet donor for the infant because she lacks the corresponding antigens. Must wash her platelets before infusing to infant to remove antibody in mother’s plasma. The most common cause of NAIT is anti-HPA-1a
What is TTP/HUS?
Thrombotic thrombocytopenic purpura/Hemolytic-Uremic Syndrome are multisystem disorders in which platelet/fibrin thrombi occlude the microcirculation. They are characterized by varying degrees of thrombocytopenia, microangiopathic hemolytic anemia, renal dysfunction, neurologic abnormalities, and fever. Patients with fulminant TTP usually have platelet counts < 50,000 and LDH levels above 1000 IU/ml; peripheral blood smear shows schistocytes. Platelet transfusion not indicated. Treatment is therapeutic plasma exchange.
What is Bernard-Soulier Syndrome?
Disorder of adhesion - For platelets to attach to collagen both von Willebrand factor (VWF) and GpIb/IX are required. VWF acts as a bridge. There is a lack of GPIb/IX in Bernard-Soulier Syndrome. Pts are giant, decreased, and not functional
What is Glanzmann’s thromboashenia?
Aggregation requires fibrinogen and the GPIIb/IIIa complex. If either are absent plt will not aggregate.
Defective GPIIb/IIIa complex is Glanzmann’s thrombasthenia.
Rare autosomal recessive disease.
Plt lacks the site for fibrinogen to attach to. Plt aggregation is affected. May have the additional complication of endogenous platelets interfering with aggregation of normal transfused platelets, thus requiring more platelet transfusions
What is HIT type 1?
It is a non‐immunologic response to heparin treatment, mediated by a direct interaction between heparin and circulating platelets causing platelet clumping or sequestration. HIT type I affects up to 10% of patients, usually occurs within the first 48–72 h after initiation of heparin treatment, and is characterised by a mild and transient thrombocytopenia (rarely <100 000/mm3), often returning to normal within 4 days once the heparin is withdrawn.
What is HIT Type 2?
HIT type II is immune‐mediated and associated with a risk of thrombosis
What is the pathophysiology of HIT?
Heparin binds to PF4 on PLT’s. This complex is very immunogenic but depends on MW of heparin
IgG antibodies to Heparin/PF4 complex are formed and activate platelets
Platelets release prothrombic secretions and are consumed in the process leading to thrombocytopenia
Excessive and unrestrained thrombin generation resulting in a prothrombotic condition, that may manifest as deep vein thrombosis, clot extension, or pulmonary embolism. Hypercoagulable state may last up to one week after last dose administration
How is HIT diagnosed?
Suspect when:
- drop >50% from baseline PLT count
- platelet count < 50 x 109/L
Drop occurs 5 to 10 days after start of Heparin in first time users. As soon as 24hrs in previously sensitized patients. (secondary response)
EIA test for heparin antibody is diagnostic
How is HIT treated?
Switch patient to danaparoid or hirudin
DO NOT switch to coumadin without using danaparoid or hirudin. Best to wait to platelets increase.
In life threatening emergencies, if the alternative anticoagulants are not available, plasma exchange may be performed.
What is the function of human platelet antigens?
Platelets play roles in inflammation; innate, adaptive, and autoimmunity; cardiovascular disease; and even cancer. However, they are most well known for their function in forming clots to stem bleeding
What are HPA’s?
Glycoproteins (GPs) expressed on the cell-surface membranes of platelets.
Platelet membrane GPs are expressed in different forms due to single nucleotide polymorphisms (SNPs) in the genes that encode them.
What are the 6 platelet membrane glycoproteins?
GPIIb/GPIIIa, GPIb alpha and beta, GPIa, and CD109
Referred to platelet specific but are often found on other cells such as leukocytes and endothelial cells
How are HPA named?
In order of discovery with high frequency antigens named “a” and low frequency named “b”
HPAs for which antibodies against only one of the two antithetical antigens have been detected are labeled with a “w” for “workshop,” such as HPA-6bw.
What are the six bi allelic groups?
Twelve antigens are clustered into six biallelic groups (HPA-1, HPA-2, HPA-3, HPA-4, HPA-5, and HPA-15).
What is the first HPA to be discovered?
HPA-1a is the platelet alloantigen that was discovered
first and is most familiar. Originally named “Zwa” and more commonly referred to as “PlA1,”
What is the function of GPIIb/IIIa?
Binding of fibrinogen by GPIIb/IIIa results
in platelet aggregation, which leads to the
formation of the “platelet plug” to stop bleeding.
What is Glanzmann thrombasthenia?
Platelet GPIIb/IIIa is absent or dysfunctional due to inherited mutations (ITGA2B, ITGB3 genes).
Serious bleeding can occur.
Patients with Glanzmann thrombasthenia who are exposed to normal platelets by transfusion or pregnancy can make isoantibodies against GPIIb/IIIa.
What HPA antibodies are the most common?
Anti-HPA-1a accounts for 80% of HPA specific antibodies
HPA-1a is on GPIIb/IIIa which is abundantly expressed making it very immunogenic
Anti-HPA-5 is second most common
Which antibody is common found in post transfusion pupura?
Anti-HPA-1a
What % of the European population is HPA-1b/HPA-1b?
2% and can make anti-HPA-1a
