Transfusion Notes

Clinical Practice Guidelines:

• Platelet transfusions are associated with higher odds of arterial thrombosis and mortality among TTP and HIT patients.
• Prophylactic platelet transfusions should be avoided in TTP patients, as there is increased risk for thrombosis.
• Platelet transfusions may be considered in life-threatening hemorrhage; however, this decision should be assessed on a case-by-case basis.

References:

• Goel R et al. Platelet transfusions in platelet consumptive disorders are associated with arterial thrombosis and in-hospital mortality. Blood (2015) 125 (9): 1470–1476.

Practical Guidance:

Thrombotic thrombocytopenia purpura is a thrombotic microangiopathy associated with either an acquired or congenital deficiency in ADAMTS13 activity. As a reminder, ADAMTS13 is an enzyme that cleaves vWF from its initial larger forms into smaller multimers. In TTP, without sufficient ADAMTS13 activity, these vWF multimers remain in an ultra-large state. The ultra-large vWF multimers avidly bind platelets, which can lead to extensive microthrombi. The microthrombi can subsequently damage the red blood cells, presenting as a hemolytic anemia.

Patients with TTP can present with a variety of signs and symptoms, but notably they will be thrombocytopenic. It is tempting to try to fix this parameter using platelet transfusions. However, transfusing these patients is not recommended; transfused platelets are bound (just as native platelets are) by the ultra-large vWF multimers, which can lead to additional extensive microthrombi. Importantly, studies have reported an increased association with arterial clots in TTP patients who have received platelet transfusions. Therefore, prophylactic platelet transfusions should be avoided in patients with TTP. There may be a role for platelet transfusion in life-threatening bleeds, however this should be assessed on a case-by-case basis.

KEY TAKE AWAYS:

• Platelet transfusions are associated with higher odds of arterial thrombosis and mortality among TTP and HIT patients.
• Although their platelet count may be low, prophylactic platelet transfusions should be avoided in patients with consumptive platelet disorders such as TTP and HIT.
• Platelets may be used in emergent settings for life-threatening bleeds, although they may not prove to be useful. This should be assessed on a case-by-case basis.
• Treatment of TTP typically involves plasmapheresis and medical management of anti-ADAMTS13 antibody production (see details in Coach’s Corner)