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3. Platelet TransfusionPlatelets are required for treatment of thrombocytopenic patients who are actively bleeding or who are at risk of haemorrhagic symptoms. Where platelet function is normal, the risk of haemorrhage depends on the platelet count.
Each patient must be assessed individually for platelet transfusion. In each case a history of the underlying disease process should be obtained. History of infection, fever, drug intake and previous transfusions should also be sought in all patients, as infections and febrile episodes increase the risk of bleeding.
Laboratory information such as platelet count, routine haematological and biochemical data related to the underlying disease, skin bleeding time and coagulation assessment are important baseline invetigations required for any patient in whom platelet transfusion is planned. It helps to decide the frequency of platelet transfusion as well as serves as a baseline for the assessment of the response to platelet therapy.
Platelets collected from random donation are the most frequently used from of platelet preparation. Blood is collected into CPD-A anticoagulant in double or triple bags and kept at room temperature until processed.
This is usually carried out by means of a short spin phase after which platelet rich plasma is obtained as supernatant.
Platelet rich plasma (PRP) can be transfused as such, however, it is clinically not acceptable due to the large volumes required for adequate therepeutic dose. Platelet concentrate is prepared by displacing PRP into a satellite bag after a secon spin and platelets are separated from the supernatent platelet poor plasma (PPP). Platelets are suspended in 50 ml plasma, containing about 5.5 x 10^10 platelets indicating a 70-75% recovery.
Single donor platelets can be obtained by plateletpheresis using a cell separator. Usually 3-4 x 1011 platelets are obtained in a volume of about 300-400 ml of plasma.
Relationship between platelet count and bleeding
a. Severe thrombocytopenia (<20,000/ui)- High risk, if no symptoms, may need prophylactic transfusion.
b. Moderate thrombocytopenia (20-50000/ui) - Platelets transfused to patients showing symptoms and those requiring surgery.
c. Mild thrombocytopenia (50-100,000/ui) - Platelet therapy usually not required.
Indications of Platelet Transfusion
The various clinical entities for which platelet transfusion may be considered are grouped according to underlying pathophysiological mechanism. Specific indications for platelet transfusion are:
1. Marrow failure
- Aplastic anaemia
- Malignant disease
- Drug toxicity
- Marrow infiltration
2. Anormality in platelet function
c. Drug indicued
3. Low platelet count with normal or increased rate of platelet production
- Massive blood transfusion
- Disseminated intravascular coagulation
- Immune thrombocytopenia
- Alloimmunized patients
- Post-transfusion purpura
- Thrombotic thrombocytopenic purpura
- Cardipulmonary bypass
Administration of Platelet Concentrate
Ideally ABO & Rh specific platelet concdíntrate should be used, but in emergency situation ABO & RH compatible or incompatible platelet concentrates may be given.
Platelets from Rh (D) positive donors should not be transfused to Rh(D) negative recipient due to the risk of Rh(D) immunization as a result of exposure to contaminating red cells.
Dosage of Platelets
Random donor platelets are usually transfused on the basis of one unit containing average 5.5 x 10^10platelets/lOkg body weight.
Total dose is therefore 3-4 x 10^11 platelets (6-8 units) for adults. This is often increase to 1.5-2 units daily in presence of splenomegely or alloimmunization.
Alternatively a single collection from a cell separator (equivalent to 6 units of platelets) may be given. Platelet concentrate can be transfused through a standard blood transfusion filter or using platelet leucodepleting filter.
Response to Platelet Transfusion
The efficiency of platelet transfusions can be assessed by clinical observations or by measuring platelet count at 1 hour and 24 hours post transfusion.
A rise of platelet count of 10,000/ui per unit of platelet concentrate transfused is anticipated in a patiEnt in absence of bleeding infection and alloimmunization platelets or HLA antigens.
The following formula is used to calculate Corrected Count Increment for a platelet transfusion.
CCI = Observed increments x body surface area (m2) / number of platelets transfused x10^11.
For example if a patient with a body surface area of 2.0 m2 is transfused with 4 x 10 number of platelets with a initial count of 15000/ul and post-transfusion count of 55,000/ul
CCI = 55000-15000/4 = 20,000/ul
This is a CCI typically for an effective platelet transfusion.
Adverse Effects of Platelet Transfusion
Platelet alloimmunization (refractoriness)
Thrombocytoponic patients receiving multiple platelet transfusion frequently become alloimmunized resulting in refractoriness to random donor platelets.
Alloimmunization is the most difficult problem facing physicians engaged in transfusion supportive care of patients with bone marrow failure. In alloimmunization the donor platelets are rapidly destroyed by antibodies directed against antigens on the surface of the platelets.
Alloimmunization has been noted in 7010O0of platelet transfusion recipients. It should be suspected when a patient fails to achieve adequate elevation of platelet count after transfusion
Measurement of platelet count 1 hour after transfusion has been show to be useful in distinguishing alloimmunization from other non-immunologic causes of refractoriness.
Other causes of refractoriness to platelet transfusion are:
1. Presence of platelet-specific antibodies (This should be suspected when perfectly HLA matched transfusion are ineffective)
2. Presence of circulating immune complexes
3. Presence of drug-induced antibodies
4. ABO incompatibility
5. WBC contamination
1. HLA-matched single door platelet transfusion. (Alternatively, transfuse large number of platelet 2-3 unit /10 kg body weight)
2. Use of cyclosporine
3. Removal of absorbed HLA antigens from platelets
5. Platelet crossmatching
6. Intravenous immunoglobulins
Graft vs host disease
This is a rare complicationS of platelet transfusion. Engraftment of donor lymphocytes already present in platelet concentrate may occur only in severely immunocompromised recipients.
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