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CHAPTER 139 above 100 × 10 /L. Patients may become refractory to platelet transfusion
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PRESERVATION AND and fail to respond for many reasons. Patients alloimmunized to platelets may
respond to platelet transfusions from class I human leukocyte antigen (HLA)-
CLINICAL USE OF PLATELETS matched donors.
Platelets can be collected by apheresis or obtained from whole blood and
pooled for transfusion. Both preparations have comparable effectiveness in
the prevention of bleeding in patients with hematologic malignancy. Plate-
Terry Gernsheimer and Sherrill Slichter lets should remain at room temperature and so are approved for only 5 days
of storage because of risks of bacterial contamination and may lose viability
within days after that. Leukocyte reduction of platelet components, either
SUMMARY upon apheresis collection or by filtration, reduces HLA alloimmunization, pre-
vents cytomegalovirus transmission by transfusion, and reduces febrile trans-
The numbers of platelet transfusions administered in the United States fusion reactions. Pathogen reduction of platelets prevents replication of RNA
increased dramatically during the 1980s, and has continued to grow as and DNA in contaminating organisms and leukocytes and may prevent alloim-
increasingly aggressive medical and surgical treatments have been developed munization and decrease transfusion reactions. Prospective clinical trials are
and become more widely available. In particular, the growth of more inten- needed to better define indications for platelet transfusion and improve upon
sive treatments for hematologic and other malignancies has spurred demands the effectiveness of transfusion therapy.
for platelet transfusion support and put pressure on platelet inventories
nationwide.
The response to a platelet transfusion is affected by platelet recovery and
platelet survival and includes the random loss of platelets in maintaining CLINICAL PLATELET TRANSFUSION
endothelial integrity. In a normal individual, weighing 70 kg, approximately
4.8 × 10 platelets per day will be consumed maintaining the endothelium, THERAPY
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less than the number of platelets in a single concentrate. However, many clin- The number of platelet units transfused in the United States increased
ical conditions can adversely affect platelet recovery and platelet survival in by 33 percent between the years 1997 and 2008 (data available at the
the circulation. Prophylactic platelet transfusion is an important part of sup- time of this writing). Of more than 2,000,000 doses of platelets trans-
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portive care of patients with hypoproliferative thrombocytopenia because fused in the United States in 2008, hematology-oncology patients used
of hematologic malignancy and the effects of its treatment with cytotoxic 32 percent, compared to the next highest usage of 15 percent in general
drugs. A morning blood platelet count of less than 10 × 10 /L appears to be medicine and 12 percent in cardiac surgery patients. Platelet transfusion
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an appropriate threshold for prophylactic transfusion. Although higher thresh- therapy is associated with multiple adverse effects, including transfu-
olds may be indicated for patients at high risk or who have active bleeding, sion reactions, infection, alloimmunization, and immune modulation.
little or no data support specific platelet count goals and a transfusion plan The cost of platelets, their short storage time, and inventory pressures
should be guided by the clinical setting. Larger doses of platelets do not confer have made appropriate use of platelet transfusions a high priority for
additional protection against bleeding in this patient population, although the management of thrombocytopenic patients to either prevent or con-
trol bleeding. Improved methods of collecting, processing, and storing
they do result in higher increments and a longer interval until the next platelet platelets will be paramount in maintaining platelet inventories in the
transfusion, a potential benefit in the outpatient setting. The platelet count at coming decade.
which an invasive procedure or major surgery can be safely performed is not
supported by randomized control studies and practice has been governed by EXPECTED RESPONSE TO A PROPHYLACTIC
retrospective data and case reports. Most minor invasive procedures and even
major surgery can be safely performed at platelet counts of 20 to 50 × 10 /L PLATELET TRANSFUSION
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whereas high-risk procedures or severe bleeding may require platelet counts The expected response to a prophylactic platelet transfusion in non-
refractory thrombocytopenic patients is assessed by two parameters:
(1) the number of platelets that circulate immediately after transfu-
sion, as measured by platelet recovery; and (2) the survival time of the
transfused platelet as measured by days-to-next-transfusion. Platelets
circulate for a shorter time in thrombocytopenic patients (≤5 days)
compared with normal subjects (8 to 10 days). This can be explained
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by the two mechanisms by which platelets are lost from circulation:
Acronyms and Abbreviations: AML, acute myeloid leukemia; AP, apheresis (1) senescence, whereby platelets are removed by the mononuclear
platelet; BC, buffy coat; CCI, corrected count increment; GVHD, graft-versus-host phagocyte system, and (2) random, whereby platelets are consumed
disease; HIT, heparin-induced thrombocytopenia; HLA, human leukocyte antigen; during hemostasis to provide endothelial support. The random loss
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HSCT, hematopoietic stem cell transplant; ITP, immune thrombocytopenia; LP, lumbar has been estimated to be 7.1 × 10 platelets/L per day. Thus, the more
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puncture; PLADO, Platelet Dose study; PRP, platelet-rich plasma; PROPPR, Pragmatic thrombocytopenic a patient is, the higher the percentage of their circu-
Randomized Optimal Platelet and Plasma Ratios study; rdWBP, random-donor whole- lating platelets that will be removed randomly versus lost by senescence
blood platelet; TOPPS, Therapeutic or Prophylactic Platelet Transfusion Study; TPO, (Fig. 139–1A). At a platelet count of 300 × 10 /L, approximately 15 percent
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thrombopoietin; TTP, thrombotic thrombocytopenic purpura; TRAP, Trial to Reduce of the platelets will be randomly removed—a fraction too small to influ-
Alloimmunization to Platelets; WHO, World Health Organization. ence the overall platelet survival. However, in a patient with a platelet
count of 50 × 10 /L, approximately 60 percent of the platelets will be
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