Question and Answers

faqs (4)

Q. Since Canadian Blood Services (CBS) began using “male” only plasma is TRALI still considered a risk of plasma or platelet transfusions?

A. The use of “male only” plasma for frozen plasma and platelet preparations is expected to reduce substantially the frequency of TRALI; this has been the experience in other jurisdictions. The rationale is to remove from the supply plasma from women who may have been immunized in pregnancy against HLA and other leucocyte-borne antigens. However, this measure will not alone eliminate TRALI, as a proportion of cases involve a different, ill-understood, mechanism. Furthermore, it is unlikely that female donors can be removed from the red cell donor pool, and since TRALI is also mediated by the plasma in the red cell units, a small number of cases mediated by female plasma will likely remain. For further information and references see the recent review by Vamvakas and Blajchman, published on-line on 4/02/09 at www.bloodjournal.org.

Q. In Bloody Easy Online Program Module 1, Question 24. A 28-year-old G1P0 has just given birth to a 7lbs girl at 38 weeks gestation. The baby is noted to have some bruising and petechiae. Prenatal course was unremarkable. Ultrasound at 18 weeks was entirely normal. Maternal CBS after delivery shows Hb 100, WBC 11 and platelet 288. CBC from baby reveals Hb 200,WBC 11 and platelet 10. What is the best choice of platelet product for the baby until a definitive diagnosis can be made? Are antibodies not from mom so best answer would be HLA crossmatched platelets as would the mom’s antibodies be present in any platelet concentrate. Is it due to no diagnosis made and time is urgent due to platelet count in newborn?

A. Transfuse maternal platelets to the baby. The rationale is that this thrombocytopenia is likely due to maternal antibodies to a paternal platelet antigen on the infant’s platelets. The quickest reliable source of compatible platelets is the mother, whose platelets will not be affected by antibody to the antigen derived from the fathers genetic constitution. Maternal platelets must be irradiated prior to transfusion, to prevent graft-vs.-host disease. In the event that maternal platelets are not a practical option, platelets negative for the antigen to which the mother is sensitised can be transfused, if available (e.g. HPA-1a antigen negative). In an emergency situation, random donor platelets may be used, while awaiting the delivery of antigen negative platelets.  

Q. The definitive routine laboratory test for diagnosis of the sickling syndromes is? Is sickledex not a screening test only? I realize it detects Hb S but does not detect Hb C/B Thalassemia etc.

A. Hemoglobin electrophoreis; Hb electrophoresis as usually done does not absolutely identify Hb S as other hemoglobins have the same electrophoretic mobility. The sickledex merely establishes the presence of Hb S without giving information on the proportion of Hb S or on the presence of other variants thus, you need both for definitive diagnosis. These tests are now being replaced with more sophisticated methods for identifying and quantifying abnormal hemoglobins.

Q. Positive DAT is not usually a feature of the hyperhemolysis syndrome associated with transfusion of sickle cell disease patients. A positive DAT is a feature of SS disease-course states not only do SS patients have elevated number of allo-antibodies especially Fya / Fyb but half have allo-antibodies especially to Kell, -E,-C and KIDD antigen stimulation. Do they not also have auto-antibodies as their own RBC’s are more easily or rapidly destroyed in the spleen post-transfusion?

A. Hyperhemolysis is uncommon but dangerous. It does not appear to be immune mediated so a positive antiglobulin test would not be found unless the patient was also one of the minority (about 10%) who have a positive DAT test. However, even if that were the case, it would not likely be relevant to the hyperhemolytic process. The mechanism of hemolysis in S/S disease is mechanically, not immunilogically, mediated.