Platelet transfusion refractoriness

Platelet transfusion refractoriness is the repeated 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 can be defined in several different ways. All measures of platelet refractoriness are defined by the timing of the post-transfusion platelet count, usually 1 hour post transfusion or 24 hours post transfusion or both.

Platelet increment (PI)

This is the simplest method, and only requires data on the platelet count before and after the transfusion.

PI = post-transfusion platelet count - pre-transfusion platelet count

Corrected count increment (CCI)

This 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.