platelet unit

Introduction

Each unit contains approximately 5.5 x 10E10 platelets, & a small amount of plasma, leukocytes & red blood cells.

Indications

• thrombocytopenia
  • platelet count < 10,000/uL with or without active bleeding*
  • platelet count < 20,000/uL with active bleeding; < 40,000/uL with pulmonary hemorrhage[2]; < 50,000/uL with clinically significant bleeding
  • platelet count < 20,000/uL with central venous catheter placement
  • platelet count < 20,000/uL with promyelocytic leukemia
  • platelet count < 50,000/uL in patients undergoing lumbar puncture or major surgery
  • platelet count < 100,000/uL for neurosurgery or intracranial bleeding
  • platelet count < 100,000/uL &/or prolonged bleeding time in post-cardiopulmonary bypass patients with active bleeding.

* only recommendation strongly endorsed by AABB

• threshold for platelet transfusion in patients needing invasive procedure may be 20,000/uL rather than 50,000/uL

* clinically stable patients with chemotherapy-induced thrombocytopenia without active bleeding do not benefit from platelet transfusions if the platelet count is >= 10,000/uL

* decreased bleeding with prophylactic transfusion of patients with platelet count < 10,000/uL who are undergoing chemotherapy or hematopoietic stem cell transplantation

Storage

• room temperature# on rotator
• shelf life 5 days

#

• cooling of platelets causes von Willebrand factor (vWF) receptor on the surface of platelets to form complexes
• alphaMbeta2 integrins on the surface of macrophages bind to beta N-acetylglucosamine residues of the N-linked glycans on GPIbalpha of vWF receptor complexes
• macrophages clear the bound platelets
• coating of the carbohydrate moiety recognized by the integrins on the surface of macrophages results in the platelets being invisible to the macrophages when cooled
• a new platelet coating procedure (i.e. enzymatic galactosylation) will likely soon lead to routine refrigeration of platelets with greatly extended shelf-life

Monitor

• platelet count within 24 hours before each platelet transfusion
• post-transfusion platelet count within 1 hour post transfusion to see if expected rise in platelet count is achieved*
• expect 5000-10,000/uL increase in platelet count for each unit of platelets transfused
  • an increase < 5000/uL is associated with alloimmunization
  • an increase of 20,000-30,000/uL for each platelet unit transfused

Procedure

Transfusion:

• in emergencies, group AB plasma & platelets can be transfused to anyone
• Rh-negative patients must receive D-negative platelets
• 1 unit of platelets for each 10 kg of body weight

Complications

Refractory response:*

• alloimmunization (generally HLA antigens, rarely platelet-specific antigens)
  • HLA-matched platelets (screen for HLA antibodies)
• clinical factors:
  • sepsis*, DIC, amphotericin, high fever, splenomegaly, bone marrow transplantation

* Risk of bacterial infection & sepsis is higher for platelet units than other blood products

• Staphylococcus aureus, 1 in 2500 platelet transfusions

* anaphylaxis: 62/100,000 platelet pools

• response occurs immediately after start of transfusion

* transfusion-associated lung injury reaction

• hypoxemia, hypotension
• delayed onset, usually 2-6 hours post-transfusion

Notes

Special preparations:

• single-donor platelets
  • alloimmunized patients refractory to random donor platelets
  • HLA-matched platelets
    • matched to all four HLA-A & B loci
    • donors homozygous at one or 2 loci with no mismatched antigens
    • donors with certain cross-reactive HLA antigens
    • crossmatched platelets
  • autologous cryopreserved platelets
    • for use with chemotherapy patients
    • 2 doses of recombinant thrombopoietin administered
    • platelets collected by apheresis on day 12
    • cryopreserved for future platelet transfusion
• platelet apheresis
  • one platelet apheresis unit is equivalent to ~ 7 units of platelets
  • leukocyte-reduced platelets

women/pregnancy

• alloimmunization from previous pregnancies
• if RhD-positive platelets must be given to an RhD-negative woman with potential for becoming pregnant, rhogam should be co-administered with the platelet units

Expected response

• 1 unit of platelets/10 kg can be expected to produce an increase of 50,000/uL
• an adequate response is defined as at least 30% of the expected response
• three platelet transfusions with a inadequate response is considered refractory
• an increase in platelet count < 10,000/uL when measured 10-60 minutes after transfusion on 2 separate occasions is considered refractory

Desmopressin (DDAVP) may be alternative to platelet transfusion when platelet dysfunction contributes to bleeding, for example uremia, cardiopulmonary bypass.

More general terms

• transfusion component

Additional terms

• platelet