Platelets and HLA Flashcards
What are the two main types of platelet products?
Apheresis platelets (single donor) and pooled platelets (from 7 buffy coats).
How are pooled platelets prepared?
7 ABO-matched buffy coats are combined with PAS-E, leukoreduced, and pathogen-reduced using psoralen + UVA light.
What is the purpose of pathogen reduction (e.g., INTERCEPT system)?
To inactivate viruses, bacteria, and parasites using amotosalen (psoralen) + UVA light.
What are the storage conditions for platelets?
20–24°C with continuous agitation; shelf life = 7 days.
Why is agitation of platelets necessary?
Facilitates gas exchange and prevents aggregation.
When is irradiation required for platelets?
For immunocompromised patients or HLA-matched/related donors to prevent GVHD.
When are platelet transfusions indicated?
For bleeding/thrombocytopenia (e.g., post-chemo, surgery) or prophylactically for very low counts.
What are contraindications for platelet transfusion?
ITP/TTP/HIT (unless life-threatening bleeding) (because all platelets are getting destroyed regardless)
Hypersensitivity to psoralen (for pathogen-reduced platelets).
Why is HLA matching important for platelets?
Platelets express Class I HLA (A, B, C). HLA antibodies (from pregnancy/transfusion) can destroy unmatched platelets, causing refractoriness.
How is platelet refractoriness managed?
Use HLA-matched or HPA-matched (for anti-HPA antibodies) apheresis platelets.
What causes TRALI?
Donor HLA antibodies (often from multiparous females) activating recipient neutrophils.
What is Post-Transfusion Purpura (PTP)?
Severe thrombocytopenia 7–14 days post-transfusion due to anti-HPA-1a (most common).
What is FNAIT?
Fetal thrombocytopenia from maternal anti-HPA antibodies crossing the placenta.
what are the risks of ABO-incompatible platelets?
Passive anti-A/B in donor plasma can cause hemolysis (e.g., Group O platelets to Group A patient).
Volume of pooled platelets?
~184 mL (vs. ~317 mL for older methods).
Leukocyte limits in platelet products?
<5 × 10⁶ (apheresis) or <10 × 10⁶ (pooled).
Residual infection risks (per donation) of platelet products?
HIV: 1 in 21.4 million
HCV: 1 in 12.6 million
A Group A patient gets a positive DAT after O platelets. Cause?
Anti-A/B from donor plasma coating recipient RBCs.
What is the priority for platelet selection?
ABO identical > compatible > alternative
How is HLA typing performed?
Microlymphocytotoxicity (CDC) or flow cytometry.
Which cells are involved in HLA Class I vs. II?
Class I: All nucleated cells (A, B, C).
Class II: Immune cells (DR, DQ, DP).
Why are platelets the most associated with bacterial sepsis?
Because the platelets are pooled
Which class of HLAs are on the surface of platelets, leukocytes, and retics?
Class I
Which class of HLAs are on immunocompetent cells such as B lymps, activated T lymphs, macrophages, and endothelial cells?
Class II
