Lecture 27 - Platelets Flashcards
1
Q
What type of HLA do platelets have
A
Class I
2
Q
What are HPA
A
- human platelet allo-antigens
3
Q
What is GPIIb/IIIa
A
- it binds natural ligands and causes aggregation
4
Q
What is GPIa/IIa
A
- binds collagen and takes part in adhesion and activation
5
Q
What is GP1b/V/IX
A
- binds von Willebrand factor and stimulates adhesion
6
Q
What are platelet allo-antibodies
A
- antibodies to non-self platelet specific antigens may be developed following exposure to non-self platelet HPA
- anatobodies to non-self class I HLA may be developed following exposure
7
Q
What is fetal/neonatal allo-immune thrombocytopenia
A
- mom develops IgG antibodies to the baby’s platelet allo-antigens
- passive thrombocytopenia
- major platelet antigens are expressed as early as 18-19 weeks gestation
8
Q
What are the clinical aspects of FNAIT
A
- approx 60% of cases detected in first pregnancy
- recurs frequently in subsequent pregnancies
- intracranial haemorrhage in 10-30% of cases
- thrombocytopenia for 1-3 weeks post partum
9
Q
Laboratory detection of FNAIT
A
- antibody screen in materna serum
- AB screen done during gestation if previous affected pregnancy
- HPA alloantigen typing of mom and dad
- anti-HPA-1A most common
10
Q
Methods used to detect HPA Antibodies
A
- PIFT-FFC
- SPAA
- ACE
- MAIPA
- Lunimex
11
Q
What is the follow up testing to antibody ID
A
- if antibodies were detected do HPA genotyping
- if HLA class I antibodies were detected
12
Q
What is the treatment of FNAIT
A
- transfusion with maternal washed platelets - preferably apheresis
- unrelated HPA typed donors are often used
- percutaneous umbilical blood sampling can be performed to monitor platelet count in utero
- treatment of mum with IVIg during pregnancy
13
Q
What is post transfusion purpura
A
- rare event characterized by an acute episode of severe immune thrombocytopenia approximately one week (5-12 days) post transfusion
- amnestic response to previous exposure
14
Q
What is the PTP frequency
A
1 per 2 million RBCs
15
Q
What occurs in PTP
A
- destruction of patient’s own platelets as well as transfused platelets result in platelet counts less than 15
- mechanism unknown
16
Q
What is the treatment of PTP
A
- IVIg
- corticosteroids
- platelet transfusion
- plasmapheresis
- in future use HPA matched units and IVIg pre-transfusion
17
Q
What is refractoriness to platelets
A
- multiply transfused patients can develop anti-platelet antibodies with a frequency of 50-90%
- most common antibody causing refractoriness is anti-HLA class I
18
Q
What is the clinical definition of PLTRE
A
- one hour post transfusion counts are required that show unsatisfactory platelet increment
- often it is recommended to have at least two episodes of unsatisfactory platelet increment before refractoriness is investigated
- corrected count increment is used to assess the success
19
Q
What are alternate causes of thrombocytopenia
A
- fever
- splenomegaly
- DIC
- drug related immune destruction
20
Q
What is the antibody testing algorithm
A
- class I HLA antibody screen
- if no HLA antibodies detecting HPA antibody may be done
- HLA typing if required
- HPA genotyping if required
21
Q
What is the treatment of PTR
A
- use of HLA matched units
- IVIg
- continuous monitoring of PRA following future transfusions
22
Q
What are the methods for HLA Ab testing in refractory patients
A
- serology methods
- solid phase assays
