Platelet Unit

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Contents 1 Introduction 2 Indications 3 Storage 4 Monitor 5 Procedure 6 Complications 7 Notes 8 More General Terms 9 Additional Terms 10 References

Introduction

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

Indications

• platelet count < 5000-10,000/ uL with or without active bleeding
• platelet count < 20,000/ uL with active bleeding [1]; < 40,000/ uL with pulmonary hemorrhage or intracranial bleeding [2]; < 50,000/ uL with clinically significant bleeding [2]
• platelet count < 50,000/ uL in patients undergoing major surgery
• platelet count < 100,000/ uL &/or prolonged bleeding time in post- cardiopulmonary bypass patients with active bleeding.

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*

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
• expect 5000-10,000/ uL increase in platelet count for each unit of platelets transfused; an increase < 5000/ uL is associated with alloimmunization

Complications

• Refractory response:*

• alloimmunization (generally HLA antigens, rarely platelet- specific antigens)
• clinical factors:

• sepsis, DIC, amphotericin, high fever, splenomegaly, bone marrow transplantation
  

• * 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

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 [3]

• 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
  

• 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

References

1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 613-614
2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, American College of Physicians, Philadelphia 1998, 2006
3. Journal Watch 22(17):133, 2002 Vadhan-Raj et al Safety and efficacy of transfusions of autologous cryopreserved platelets derived from recombinant human thrombopoietin to support chemotherapy-associated severe thrombocytopenia: a randomised cross-over study. Lancet 359:2145, 2002 PMID: [1]
4. Journal Watch 23(21):170, 2003 Hoffmeister KM et al Glycosylation restores survival of chilled blood platelets. Science 301:1531, 2003 PMID: [2]
   - Couzin J Medicine. Sugary cloak protects platelets from the cold. Science 301:1457, 2003 PMID: [3]
5. Platelet Transfusion Therapy: NIH Consensus Statement [4]
6. National Guideline Clearinghouse Guideline for platelet transfusion thresholds for pediatric hematology/oncology patients. C17 Council (Alberta, Canada) ngc-guideline: [5]

platelet unit