platelets

Platelets, also known as thrombocytes, are one of the components of blood, along with red blood cells, white blood cells, and plasma, the fluid component. Platelets are small cell fragments of large bone marrow cells known as megakaryocytes and derive the name from their plate-like shape. Platelets clump together and form blood clots to stop bleeding and to heal wounds after an injury.

Platelets collected from donors are administered as intravenous transfusions to treat thrombocytopenia, a condition with an abnormally low count of platelets. Normal platelet count in adults may range from 150,000-300,000 per microliter. Thrombocytopenia can make a person more prone to bleeding and bruising, and put them at high risk for excessive and uncontrolled bleeding from even minor injuries. Platelet transfusions are given to patients with thrombocytopenia in the following circumstances:

• Actively bleeding patient: Target is to keep platelet count above 50,000/uL, and above 100,00/uL in case of central nervous system bleeding.
• Preparation for an invasive procedure: Transfusion is given if the patient has severe thrombocytopenia and is deemed to have a high risk for bleeding. Platelet threshold levels required can vary from 10,000/uL to 100,000/uL or more depending on the procedure to be performed.
• Prevention of spontaneous bleeding: Prophylactic platelet transfusion is given to patients without fever (afebrile) with platelet counts below 10,000/uL due to bone marrow suppression. Higher platelet thresholds are used in patients who are febrile or septic or patients with acute promyelocytic leukemia. Thresholds can vary depending on the patient and their clinical condition.

Platelets are collected in two ways:

• By isolating and pooling platelets from units of donated whole blood
• By collecting platelets via apheresis directly from a donor

Apheresis is a process by which a donor’s blood is passed through a medical device that selectively removes platelets, with or without some white cells and plasma. The red blood cells and plasma are infused back into the donor. The advantage of apheresis platelets over whole blood derived (WBD) pooled platelets is that the recipient is exposed to only one donor and can be matched for blood type, human leukocyte antigen (HLA) type and cytomegalovirus (CMV) status.

• Prophylactic platelet transfusion is avoided in thrombocytopenic patients with blood disorders that have a high propensity for clotting (pro-thrombotic), it can increase the risk for thrombosis. Platelet transfusion may be given to such patients who are actively bleeding or anticipated to be at risk from a required invasive procedure. Conditions contraindicated for platelet transfusion include:
  • Immune thrombocytopenia (ITP), in which the immune system destroys megakaryocytes and circulating platelets
  • Thrombotic thrombocytopenic purpura (TTP) that causes small blood clots to form in the small arteries all over the body
  • Heparin-induced thrombocytopenia (HIT), an immune system-related complication from heparin use that causes clot formation and low platelet count
• Platelet transfusion should be done only for bleeding in thrombocytopenic patients with inherited or acquired defects in platelet function.
• Liver disease and disseminated intravascular coagulation (DIC) are two conditions that can cause a complex mixture of clotting and bleeding defects. Platelet transfusion in such patients should be reserved only for active bleeding or high risk for bleeding.
• Patients should be monitored for signs of a transfusion reaction, including vitals, before during, and after transfusion. Transfusion should be stopped if transfusion reaction is suspected, the patient should be assessed and stabilized, and the blood bank notified to initiate an investigation.
• Platelet products have an increased risk of significant bacterial contamination and sepsis compared to other blood products because platelets must be stored at room temperature since they rapidly lose function when refrigerated. Patients should be monitored for signs of infection and promptly treated.
• Platelet transfusion has a risk for transmission of viral infections including HIV, CMV, hepatitis B and C viruses, bacterial and parasitic infections.
• If ABO (blood groups) identical platelets are not available, platelets from ABO plasma compatible donors may be used without significant problems, but can result in suboptimal responses.
• Platelet products contain a small amount of red blood cells. Rh-compatible platelets should be used if possible to prevent the formation of anti-D in Rh negative individuals, especially in women who are pregnant or may become pregnant.
• Platelet transfusions may induce formation of HLA antibodies and rarely platelet specific antibodies (HPA-1a) that may cause immune refractoriness for future transfusions, particularly for patients that require numerous platelet transfusions. Reducing leukocytes in the platelet product may reduce HLA sensitization. These patients may benefit from HLA matched or HPA-1a negative apheresis platelet transfusions if available.
• White cells in the platelet products may attack host tissue, a condition known as transfusion-associated graft-versus-host disease (TA-GVHD). Irradiated platelet products should be used for patients at increased risk for TA-GVHD.
• Patients that are CMV seronegative or whose CMV status is unknown and are at increased risk of symptomatic CMV infection should receive CMV reduced risk platelets.

Common side effects of platelets include:

• Transfusion-transmitted infections and septic reactions
• Production of antibodies against donor platelets (alloimmunization)
• Hemolytic transfusion reactions that destroy red blood cells 
• Feverish (febrile) non-hemolytic reactions
• Transfusion related acute lung injury (TRALI)
• Transfusion-associated graft-versus-host disease (TA-GVHD)
• Transfusion-associated circulatory overload (TACO)
• Allergic reactions such as:
  • Hives (urticaria)
  • Itching (pruritus)
  • Wheezing
  • Shortness of breath (dyspnea)
  • Low blood pressure (hypotension)
• Serious allergic (anaphylactic) reactions including:
  • Swelling under the skin and mucous membrane (angioedema)
  • Respiratory distress
  • Shock
• Post-transfusion bruising (purpura)

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

• Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
• Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
• Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
• Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

Thrombocytopenia

Adult:

• Typical dosing for an adult is a pool of 6 whole blood derived (WBD) units of platelets or one unit of apheresis platelets.
• This is expected to raise the platelet count by 30,000-60,000/uL in a 70 kg patient.

Pediatric:

Neonates and small children

• Transfusion of 5-10 mL/kg should raise the platelet count by 50,000-100,000/uL.

Children weighing more than 10 kg

• Transfusion of 1 unit of whole blood-derived platelets per 10 kg should raise the platelet count by 50,000/uL

Dosing considerations

• Transfused platelets have a short life span and will need to be re-dosed within 3-4 days if given for prophylaxis.
• Suboptimal increases can be seen due to non-immune destruction or immune refractoriness. If suboptimal increases are suspected, the corrected count increment (CCI) can help determine if the response is truly suboptimal based on the amount of platelets transfused compared to body surface area.
• The CCI can also assist in determining whether the response is due to immune refractoriness or non-immune causes.

Other Indications and Uses

• Platelet transfusions may be given for thrombocytopenia or platelet dysfunction to treat active platelet-related bleeding or as prophylaxis in those at serious risk of bleeding.
• Typical indications include leukemia, myelodysplasia, aplastic anemia, solid tumors, congenital or acquired/medication-induced platelet dysfunction, central nervous system trauma, and patients undergoing extracorporeal membrane oxygenation or cardiopulmonary bypass may also need platelet transfusion.
• Thresholds for transfusion due to thrombocytopenia have been controversial. However, it is generally accepted that a count of 50,000/uL is sufficient for most invasive procedures including most surgeries. Platelet counts of greater than 100,000/uL are recommended for ophthalmic and neurosurgery. Higher transfusion thresholds may be appropriate for patients with platelet dysfunction.
• Probably the most controversial threshold is for the clinically stable patient with an intact vascular system and normal platelet function. Prophylactic platelet transfusions may be appropriate at 5,000- 10,000/uL to prevent spontaneous bleeding. Patients with autoimmune destruction of platelets, such as ITP, may not receive therapeutic benefit from prophylactic transfusion, but may however benefit from transfusion if bleeding.

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

• Platelets have no known severe, serious, moderate, or mild interactions with other drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

• Cytomegalovirus-seronegative or CMV reduced risk (leukocyte reduced) platelets should be used in pregnant or breast-feeding women who are CMV-seronegative or whose CMV status is unknown.
• Platelet products contain a small amount of red blood cells. Rh-compatible platelets should be used if possible to prevent the formation of anti-D in Rh negative women.