Platelets & Granulocytes Flashcards
What antigens are expressed in platelets?
ABH, HLA, HPAs (significant), also I/P/Lewis and Cromer (insignificant)
What HPAs are located on GpIIb/IIIa (CD41/61)?
HPA-1
HPA-3
HPA-4
What is the most important HPA and what is its frequency?
HPA-1A/B. AA (72%), AB (26%), BB (2%)
What HPAs are located on GP1b/V/IX (CD42)?
HPA-2
HPA-12
What is the number 2 cause of NAIT?
Anti-HPA-5a antibodies, found on GpIa/IIa (a collagen receptor).
Where are ABH carried on platelets?
On GpIIb and PECAM-1/CD31. Note that A2 patients express so little A their platelets are effectively group O.
Recall some minor platelet antigens.
CD109 (houses HPA-15)
GPIV/CD36
GPVI
What size pool is needed to adequately find HLA-matched donors? What matches are best?
1000-3000 donors. A, B1X, B1U, B2UX are acceptable (no mismatches, cross-reactivity OK).
What is antibody specificity prediction (ASP)?
Giving platelets with HLA antigens against which there are no known antibodies (despite being non-identical).
How is platelet crossmatching performed
Solid phase red cell assay (SPRCA)
How is FNAIT tested for? How rapidly can it develop?
Test maternal serum for antibodies and genotype father. Can develop intra-pregnancy.
What drugs can cause thrombocytopenia?
Sulfas, quinine, vancomycin, HEPARIN, GpIIb/IIIa antagonists.
Why are platelets in HIT activated?
The anti-PF4 antibodies cawn also activate plt FcyRIIa.
What testing methods exist to identify platelet antigens/antibodies?
Glycoprotein-specific assays (antigen captures, ACE/MACE/MAIPA)
Whole platelet assays (SPRCA, flow cytometry)
Genotyping
How is testing in ITP done?
First of all, it’s not always necessary. But most tests look at eluates from platelets for specificity against platelet glycoprotein antigens.
Granulocyte antigen-antibody interactions are implicated in what conditions?
Neonatal alloimmune neutropenia (NAN) TRALI FNHTRs Autoimmune neutropenias (AIN) Granulocyte refractoriness
What is HNA-1 located on?
FcyRIIIb (CD16b, 100-200k copies per cell)
What is CD177?
Some surface marker only notable for housing HNA-2. Up to 11% of patients are null and can develop antibodies.
What is the most important HNA antigen? Where is it located?
HNA-3, located on CTL3.
What HNAs are housed in CD11?
HNA-4 (CD11b/18)
HNA-5 (CD11a/18)
What blood group antigens are on neutrophils?
NOT ABO/RH
MHC-I/II
Neonatal alloimmune neutropenia
Maternal alloimmune response against fetal HNA-1a, -1b, -2, or others. Can be life threatening, treated with antibiotics, IVIG, G-CSF and PLEX
How is granulocyte testing performed?
Very difficultly, because of shortgevity of cells and interference of HLA antibodies.
What granulocyte tests exist?
Granulocyte agglutination test (pt serum + granulocyte)
Immunofluorescence (wash neutrophils, add fluoro-AHG)
Luminex
HNA typing (genotypic)
How frequently are platelet units bacterially contaminated? How often do they cause serious reactions? Fatal reactions?
About 1 in 1000-3000. Only about 1 in 6 of these will cause any reaction, and even fewer will cause serious reactions. Perhaps 0.5-1 in a million are fatal.
What organisms most often cause fatal septic platelet transfusion reactions?
Gram-negative rods! GPCs are more common but these are generally not fatal.
How can bacterial contamination of platelets be avoided?
Use screening questions and temperature. Clean the site thoroughly and divert the first portion of the draw (doesn’t stop GNR bacteremia). Use single donor packs, not pools.
What are the main bacterial platelet contamination detection methods currently in use?
BacT/ALERT: 4-8mL in aerobic+anaerobic bottle. Colorimetric CO2 detection.
Pall eBDS: 2-3mL in a bag with tryptic soy broth. Measure oxygen consumption (misses anaerobes).
How can bacterial contamination in platelets be reduced or inhibited?
Cold storage
Pathogen-reduction (INTERCEPT, Mirasol, Theraflex) - Amotosalen, riboflavin, potassium/magnesium?
How are granulocyte donors primed? What are the side effects?
G-CSF (newer) and/or steroids, either generally given about 12 hours ahead of harvest. Musculoskeletal pain is common. Long-term effects are not well described.
What are the classes of platelet HLA matching?
A (4 loci matched)
BU (3 loci matched–homozygous for one)
BX (3 loci matched, 1 CREG)
C/D/R (mismatched)
What disease states leave patients at very high risk of alloimmunization against HPAs?
Glanzmann’s thrombasthenia, Bernard-Soulier (congenital absence of these antigens)
What is the cause of FNAIT? Any associations?
Maternal anti-HLA-1a (or 4b) antibodies causing isolated fetal thrombocytopenia. Penetrance is associated with HLA-DRB3*01.
Post-transfusion purpura
Mostly seen in women who have anti-HPA-1a antibodies. Can be fatal. Requires positive serology to diagnose. Treated with steroids/IVIG and maybe TPE.
What is “reverse PTP”?
Thrombocytopenia resulting from transfusion of a plasma-rich product from an HPA-1a-immunized patient (usually pregnant women; downtrending along with TRALI).
What is the full half-life of a platelet in vivo?
10.5d
At what pH should platelets be kept above?
6.2 (below, platelets agglutinate and lyse)
What are the platelet bags made of? Why?
PVC, plus plasticizers such as DEHP. Must be gas-permeable.
What is the required count for apheresis platelets?
> 3 x 10^11 in at least 75% (90%?) of units
How many red cells can contaminate a platelet before RHD alloimmunization is a concern?
0.03mL of red cells; above this give RhoGAM. This is less than the amount expected in apheresis (0.001mL)
What percentage of alloimmunized patients are refractory?
Only 30%
What HPA is especially associated with platelet refractoriness?
GPIV (absent in many African americans, anti-GPIV antibodies cause refractoriness)
List HLA platelet matches by effectiveness.
A > B1U > B2U > B1X > B2UX > B2X > C,D
Time to peak granulocyte mobilization
8-16 hours (average 12) using a G-CSF/steroid regimen.
What is the usual red cell content of a granulocyte unit?
~30mL RBCs (~10% hematocrit)
How does lack of IDM test resulting get resolved?
Select repeat donors who have had IDMs in last 30 days
Extend results and release at medical director discretion
During granulocyte collection, how much blood is processed, and for how long?
It is a typical apheresis procedure, processing 7-10L WB and taking about 100min on average.
What are the consequences of HES use?
Possible anaphylactic or flu-like reactions.
Decreased von willebrand factor and increased aPTT
What are pooled granulocytes?
A product made from whole blood using buffy coats, only used in Europe, not the US.
What is the required count for granulocyte?
Minimum 1 x 10^10 granulocytes in at least 75% of units.
From where can PRP be sourced? How is it collected?
Autologous or allogeneic. Dozens of collection methods with hetereogeneous and crappy literature. Note that some products may contain thrombin as a platelet activator.
What is the rationale behind therapeutic PRP?
Platelets carry chemokines which promote wound healing by stimulating mesenchymal and endothelial proliferation and angiogenesis.
What different types of PRP products exist?
Pure PRP
Leuko-rich PRP
Plt-rich fibrin (stronger clot and gel matrix)
Leuko- and plt-rich fibrin
What is the evidence in support of PRP?
Scant. Most injury settings derive some pain benefit but do not show faster return to function.
