Platelet transfusion refractoriness

Platelet transfusion refractoriness is the failure to achieve the desired level of blood platelets in a patient following a platelet transfusion. The cause of refractoriness may be either immune or nonimmune based. Among immune-related refractoriness, antibodies against HLA antigens are the primary cause. Non-immune causes include splenomegaly (enlargement of the spleen), fever, and sepsis.

Cause

Platelet refractoriness can be due to immune causes or non-immune causes. Non-immune causes account for over 80% of cases of platelet refractoriness, and sepsis is one of the most common non-immune causes. HLA alloimmunization is the commonest immune cause of platelet refractoriness.

Non-immune causes

• Sepsis

• Fever

• Disseminated intravascular coagulation

• Splenomegaly

• Treatment of infection, antibiotics (vancomycin), antifungals (amphotericin B)

• Graft-versus-host disease

• Hepatic veno-occlusive disease

• Bleeding

Immune causes

• Alloantibodies to platelet antigens
  • Human leucocyte antigen (HLA) antibodies
  • Human platelet antigen (HPA) antibodies

• Immune complexes

• Other antibodies
  • Drug-related antibodies

Diagnosis

Platelet transfusion refractoriness is typically diagnosed using the corrected count increment, which requires 4 items of information:

1. Pre-transfusion platelet count
2. Post-transfusion platelet count: the post-transfusion blood sample for this measurement should be collected 10–60 minutes after the transfusion has been completed
3. Body surface area
4. Number of platelets transfused: the blood bank maintains records of the estimated number of platelets in each unit. Current requirements in the US stipulate that a unit of apheresis platelets must contain at least 3.0 x10¹¹ platelets.

The CCI is calculated as follows: CCI= (Post-transfusion platelet count - Pre-transfusion platelet count)(BSA) ÷ (number of platelets transfused).

A CCI greater than 7500 indicates a sufficient post-transfusion increment, whereas a CCI less than 7500 is considered diagnostic of platelet refractoriness.

Immune-mediated refractoriness usually shows little or no increment in the immediate post-transfusion platelet count. Non-immune refractoriness may show an initial rise in platelet count, but a subsequent 8-hour or 12-hour post-transfusion sample shows a return to the baseline platelet count.