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Platelet Products
Product Names
Platelet products include those derived from whole blood and those collected by apheresis. While the FDA has a nomenclature specific to each method of collection, many terms are in common use. This creates confusion in published papers and with ordering physicians. The FDA calls platelets derived from whole blood “platelets,” and these are sometimes also referred to as whole blood–derived platelets , random donor platelets , and platelet concentrates . Platelets collected by apheresis are called “platelets, pheresis” by the FDA, which are sometimes referred to as single donor platelets, apheresis platelets, and plateletpheresis. The method of collection does not reflect or define a platelet dose. Dose is patient-dependent and can vary given the clinical circumstance but usually approximates 3–4 × 10 11 platelets for an adult and 10 mL/kg in pediatrics. As whole blood–derived platelet units typically contain 5.5 × 10 10 platelets, 4–6 units must be “pooled” to make a dose. Many apheresis-derived platelet collections contain 2–3 times the required minimum of 3 × 10 11 platelets and thus are “split” to make multiple platelet doses from a single collection.
Description
Platelets are an essential component of hemostasis, and deficiencies in platelet number or function can result in bleeding. Thrombocytopenia and/or platelet dysfunction may result from congenital diseases, medications, liver or kidney diseases, sepsis, disseminated intravascular coagulopathy (DIC), hematologic diseases, massive transfusion, and cardiac bypass or extracorporeal membrane oxygenation. Clinical signs of thrombocytopenia or platelet dysfunction include petechiae, easy bruising, or mucosal bleeding. The average in vivo life span of a platelet is ∼10 days, but that of a transfused platelet is ∼4–5 days. A platelet’s life span is shortened by bleeding, DIC, splenomegaly, platelet antibodies, medications, sepsis, endothelial cell or platelet activation, and thrombocytopenia.
Indications
Platelet transfusions are used for prophylaxis to prevent bleeding or for treatment of bleeding in patients who have thrombocytopenia, qualitative defects in their platelet function (inherited or acquired secondary to disease or antiplatelet medications), or in the setting of massive transfusion. AABB guidelines recommend a prophylactic platelet transfusion threshold of 10,000/μL; a higher threshold may be considered in patients with fever, bleeding, or sepsis. A threshold of 10,000/μL was recently validated in a large retrospective analysis of thrombocytopenic hematology/oncology patients undergoing stem cell transplant or chemotherapy, in which a platelet count of <5000/μL was associated with increased bleeding. However, in the setting of autologous hematopoietic cell transplantation for adult patients, recent ASCO guidelines recommend platelet transfusions at the first sign of bleeding rather than prophylactic transfusions. The threshold is increased to >20,000/μL for central venous catheter placement and >50,000/μL before lumbar puncture, biopsy, or nonneuraxial surgeries. For procedures involving neuraxial locations, such as the eye or brain, and for major surgery, a threshold of >100,000/μL is suggested. A threshold of >50,000/μL should be considered in actively bleeding patients. Thresholds for neonates are not clearly defined, and practices vary widely; for invasive procedures or bleeding, platelet counts are kept >50,000/μL and >100,000/μL in extremely ill, premature infants. Prophylactic platelet transfusions are generally administered for platelet counts <20,000/μL in neonates and <50,000/μL in extremely ill premature or critically ill neonates.
Relative Contraindications
Platelet transfusions are generally contraindicated in patients with thrombotic thrombocytopenic purpura (TTP) or heparin-induced thrombocytopenia (HIT) unless there is severe or life-threatening hemorrhage because they may increase the risk of thrombosis. In addition, a recent multicenter, randomized controlled trial associated platelet transfusions with greater mortality in patients with acute, spontaneous primary intracerebral hemorrhage on antiplatelet therapies. Thus, platelet transfusions may be contraindicated in this setting.
Whole Blood–Derived Platelets
In the United States using the platelet-rich plasma method ( Chapter 9 ), per CFR and AABB Standards, whole blood–derived platelet units must contain ≥5.5 × 10 10 platelets in 90% of the units tested. Before issuing whole blood–derived platelets, the platelet products must be pooled to make a sufficient adult dose. Transfusion services may pool platelet concentrates, which require bacterial screening and expire in 4 hours postpooling. The FDA has approved a system for prepooling, leukoreducing, and bacterial testing of platelet concentrates. These platelets are referred to as “prestorage pooled platelets.” Four to six units of platelets may be pooled using this system to achieve an FDA-approved dose of 2.2–5.8 × 10 11 .
Apheresis
Apheresis platelets are collected into an ACD-A (citric acid, sodium citrate, dextrose) solution as either platelet-enriched plasma or as a platelet pellet that requires resuspension in concurrently collected plasma. Apheresis-derived platelets are collected as leukoreduced.
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