PLASMA TRANSFUSION THERAPY
Darrell J. Triulzi, M.D.
Centralized Transfusion Services
Platelets transfusions have become an integral
part of the care for numerous patients with disease or treatment related thrombocytopenia.
Continuing concern over the risks and costs of platelet transfusion have provided the
impetus to continuously review appropriate indications for their use.
A random donor platelet concentrate is prepared from a
single unit of whole blood and contains approximately 0.6 x 1011 platelets and 50 ml of
plasma. A therapeutic dose is 1 unit/10 kg body weight pool or approximately 6-7 units in
an adult. Each unit would be expected to raise the platelet count by 5,000 - 10,000/ul. A
single donor platelet is obtained by apheresis and contains 3-6 x 1011 platelets in
250-450 ml plasma. Thus, a single donor platelet is equivalent to a 6-8 unit pool of
random donor platelets and would constitute one therapeutic dose. Platelets may be stored
for up to 5 days at room temperature. Once pooled they must be given within 4 hours to
Complications of Platelet Transfusion
Platelet transfusions are capable of transmitting blood
borne pathogens with a risk similar to that associated with whole blood, red cells, or
plasma. Since platelets are typically administered in pools of 6-8 units, the risk is
increased with the increased number of donor exposures. Current estimates per tested unit
for transmission of hepatitis C is >1:3,300, HIV 1:400,000, and hepatitis B 1:200,000.
Platelet transfusions are also associated with other risks including fever-chill
non-hemolytic transfusion reactions and allergic transfusion reactions. These can occur in
as many as 30% of platelet transfusion episodes. Lastly, white cells contaminating
platelet products may induce HLA antibodies in the recipient; a process called
alloimmunization. HLA antibodies in the patient may bind to transfused platelets resulting
in poor platelet increments (refractoriness). The risk of alloimmunization is 50% in
patients receiving multiple platelet transfusions. This can be reduced to 20% by removing
the white cells from the product prior to transfusion (leukodepletion). Limiting the
number of platelet transfusions may reduce the risk of these complications.
Indications For Platelets In The Non-bleeding Patient
The prophylactic use of platelets in severely
thrombocytopenic patients has been well entrenched in transfusion practice. Traditionally
a platelet trigger of 20,000/ul has been used. This number is based on a 1962 study of
leukemia patients concomitantly treated with aspirin. Several recent studies have
questioned the validity of this trigger and have shown that patients without other risk
factors for bleeding can be safely observed until the platelet count drops to 10,000/ul or
even less. Patients with risk factors for bleeding including: infections, coagulopathy,
heparin therapy, splenomegaly, or sepsis may require higher thresholds. It is
controversial whether fever without other evidence of infection warrants use of a higher
Indications for Platelets in Bleeding Patients or
Patients Undergoing Invasive Procedures
Platelet transfusion are indicated in patients with
active bleeding and platelet counts <50,000/ul. Minor bleeding confined to the skin
(petechiae, ecchymosis) generally does not require platelet transfusion to this level.
Platelet transfusions are also indicted in patients who will undergo invasive procedures
with platelet counts <50,000/ul. Patients with a coagulopathy or bleeding in a critical
site (i.e., CNS, lungs) may require transfusion at higher levels.
Indications for Platelets in Patients with Platelet Dysfunction
The utility of platelets in this setting depends on the
etiology of platelet dysfunction and is independent of platelet count. Platelet
transfusions may be beneficial in bleeding patients post-cardiac bypass, with
aortic/ventricular assist devices, or on extracorporeal membrane oxoygenators. Patients
with a recent history of aspirin use may benefit from platelet transfusion if they are
bleeding or will undergo an invasive procedure. Platelet transfusions are generally not
indicated in patients with platelet dysfunction due to uremia or von Willebrand's disease.
Patients with immune thrombocytopenic purpura or thrombotic thrombocytopenic purpura
should not be treated with platelet transfusions unless bleeding is life threatening.
For questions or further information please contact
Darrell J. Triulzi, M.D. - (412) 209-7304
Copies of the Transfusion Medicine Update can be
obtained by contacting
Deb Small - (412) 209-7320
Copyright © 1997, Institute For Transfusion Medicine