Platelet transfusion therapy

A general change of the platelet transfusion policy from apheresis platelet concentrates to pooled platelet concentrates is associated with a sharp increase in donor exposure and infection rates

BACKGROUND

We compare the actual with the potential donor exposure and possible infection rates in the Hanover Medical School (MHH) platelet (PLT) transfusion recipients if the current MHH standard of apheresis PLT concentrate (A-PC) supply would be replaced by a pooled PLT concentrate (P-PC) transfusion regimen.

DONORS PATIENTS AND METHODS

The electronic records of the MHH Institute of Transfusion Medicine and the MHH Department of Medical Controlling were evaluated to assess the development of PLT needs and supply at MHH from 2003-2006. For 2006, we evaluated all PLT transfusion recipients with respect to their overall transfusion needs, classified them for low and high PLT transfusion needs, and related them to the diagnostic groups that underlie their PLT demands. We assumed a P-PC preparation procedure using 4 whole blood-derived buffy coats for all calculations for potential donor exposure. To predict the possible infection rates of an unrecognized viral infection with low prevalence in the general population to A-PC or to P-PC recipients and the influence of neutralizing agent specific antibodies (NAB), we established a mathematical contamination/infection model based on the current PLT transfusion mode and data about GBV-C virus infection among Hanover blood donors.

RESULTS

From 2003 to 2006, the 1,300-1,400 persons comprising MHH apheresis donor pool covered a 36% increase in PC transfusions. The exclusive use of P-PCs instead of A-PC would require a total of 36,240-49,276 whole blood donations to meet MHH demands, corresponding to a more than 1 log step increase in donor exposure. For individual hematological patients, the change to P-PCs would imply an 80-125%, for individual surgical patients a 40-50% higher donor exposure. Our infection model revealed an approximately 4 times higher infection.

CONCLUSIONS

A change to P-PC would imply a more than one log step higher donor exposure, and an unrecognized infection with a prevalence around 1% leads to an up to 4 times higher infection rate. A general change in the PC transfusion policy that favors P-PCs is dangerous and must be avoided.

Calculated platelet dose: Is it useful in clinical practice?

The corrected count increment (CCI) can standardize assessment of platelet transfusions by correcting for patient's body surface area (BSA) and platelet dose (PD). By using a fixed CCI and a desired post-transfusion platelet count, CCI formula can be used to calculate PD. Our transfusion service has used the following formula since May 1990, to determine the number of platelet units to transfuse in non-bleeding patients: 1 where, 7,000 is expected platelet count increment per unit transfused, and 1.7 is BSA in square meters in a normal adult. To evaluate its usefulness, a retrospective review was performed of all 2,202 platelet transfusions at our level-one trauma center, between 1/1/98 and 12/31/00. Eighty-three transfusions in 69 adult patients, in which a calculated PD was determined prior to transfusion, were evaluated for platelet increments at 1, 1-18, or 18-24 hours post-transfusion. Transfusions that used the calculated PD (n = 49) were compared with those that were based on clinical judgment alone (n = 34). These two groups were comparable in their pre-transfusion platelet counts, ABO compatibility, and unit storage duration. The mean calculated PD transfused in the first group was 6 U +/- 1 standard deviation, which was not different from the second group (P = 0.2). There was no difference in the platelet count increments at 1, 1-18, or 18-24 hours post-transfusion. This study suggests that using a PD based on the CCI formula does not reduce platelet usage when the routine PD is six or less platelet concentrates.

Revisitation of the clinical indications for the transfusion of platelet concentrates

Platelet transfusion is indicated when the expected benefits of increasing the number of functional platelets in the patient's circulation outweigh the potential risks generated by exposing the patient to allogeneic, manipulated and stored blood products such as platelet concentrates. Although reassuring evidence has been collected indicating that current risks associated with blood transfusion are lower than those of several voluntary and involuntary human activities, balancing benefits and risks of platelet transfusion may not be easy in a proportion of patients and in a number of conditions. To facilitate this task, guidelines have been developed, with particular attention to cancer patients. As witnessed by the most recent guidelines, over the last few years there has been a progressive, although not absolute, consensus on: (i) the routine use of platelets as a tool to prevent hemorrhage in oncohematology (the so called 'prophylactic approach') as opposed to limiting platelet transfusion to actual bleeding episodes (the so-called 'therapeutic approach') and (ii) lowering the trigger for prophylactic platelet transfusion in stable oncohematology recipients from 20 x 109 to 10 x 109 platelets/L. This has been accompanied by a reduction of platelet use per oncohematology patient of about 20%, an important outcome in view of the progressive increase of platelet demand due to more aggressive therapy in cancer patients. In selected clinical conditions, specific triggers ranging from 30 x 10(9) to 100 x 10(9) platelets/L have been recommended, with higher values when surgical procedures are required for the patient's treatment. Indications and trigger values proposed in the guidelines must be considered within the context of careful clinical evaluation of each patient, with a clear appreciation of the power of discrimination of automated platelet counters at low counts, and of the quality and local availability of platelet products for emergency.