Ch. 10 - Special transfusion situations Flashcards
How does neonatal alloimmune thrombocytopenia present?
Newborns presents with symptoms ranging from mild petechiae to major bleeding including ICH. This can also be seen in utero. This may be seen in the first pregnancy and can reoccur in subsequent pregnancies.
Describe the pathophysiology of neonatal alloimmune thrombocytopenia.
Alloantibodies are directed against incompatible fetal platelet antigens. These IgGs cross placental barrier and cause thrombocytopenia lasting for days following birth.
What antigens are responsible for neonatal alloimmune thrombocytopenia?
HPA1a (80% of cases)
HPA5b (10%)
HPA1b (5%)
HPA3a (<5%)
How is NAIT managed?
Transfusion of platelets either for active bleeding or for goal of 30k. If maternal platelets are used, they must be washed (and irradiated).
IVIG
If in utero, cesarian delivery.
Describe the pathophysiology of HDFN.
Passively acquired maternal antibodies destroy fetal RBCs via extravascular hemolysis. These antibodies may be naturally occurring or acquired. Kernicterus or even hydrops may result.
How can fetal hydrops result from HDFN?
RBC destruction stimulates extramedullary hematopoiesis, which in turn can impair liver function due to portal hypertension, resulting in hypoproteinemia.
What subclasses of IgG are most effective at hemolysis?
IgG1 and IgG3
Which alloantibodies are most potent in causing HDFN?
Anti-D
Anti-K
Anti-c
Anti-E
What is the impact of maternal type O blood group on HDFN?
Mothers that are type O are more likely to develop HDFN as they are more likely to have naturally occurring IgG-class ABO antibodies.
Why is ABO incompatibility not a major cause of HDFN?
Fetal RBCs do not express much ABO antigen, and placental expression of ABO absorbs some of the maternal antibodies.
How is HDFN managed in early pregnancy?
During the first prenatal visit, mothers should be typed, screened, and titered. Father’s blood can be tested for any corresponding antigen.
What is the role of checking titer levels in HDFN? What levels are important?
Determining titer levels helps to stratify risk. In general, most at 1:16 or 1:32 are significant (1:8 for Kell)
How is HDFN managed during pregnancy?
If needed, amniotic or fetal DNA can be tested for risk. Ultrasonography and doppler velocimetry are used to check for anemia (Lyle curve). Continue to titer.
What can be done for severe HDFN during late pregnancy?
Intrauterine transfusion if Hct <30% following cordocentesis. This is done with group O, leukoreduced, CMV-negative, irradiated and volume-reduced blood.
How is HDFN managed during the neonatal stage?
Phototherapy and IVIG for mild cases. Exchange transfusion if severe.
When is RhIg normally administered?
Once at 28wks of gestation, once at delivery, and again at anytime materno-fetal hemorrhage is suspected.
What are the Rosette and Kleihauer-Betke tests?
Rosette: Add anti-D and indicator RBCs to fetal blood, count the rosettes that form.
Kleihauer-Betke: Treat a blood smear with acid, and quantify the residual blood (HbF is resistant)
What defines platelet refractoriness?
A less than expected increase in platelet count after transfusion of 2+ ABO-matched platelet products that are less than 72yo.
What are some non-immune causes of platelet refractoriness?
Bleeding, fever, sepsis, hypersplenism, DIC, drugs.
What is the cause of immune-mediated platelet refractoriness?
Usually antibodies to Class I HLA molecules, but cases have been described with HPA and ABO antibodies.
What is the posttransfusion platelet recovery (PPR) metric?
A less popular way to determine response to platelet transfusion.
Measure count prior to transfusion, repeat after transfusion. Divide the increment by the number of units and patient’s blood volume. Should be >30%
What is the corrected count increment (CCI) metric?
The preferred means to determine response to platelet transfusion.
Multiple the platelet increment by body surface area divided by the number of platelets transfused. Should be >7500.
What is the difference between threshold PPR or CCI counts in identifying immune and non-immune platelet refractoriness?
Non-immune reractoriness is defined at lower PPR/CCI thresholds taken over a longer period, reflecting platelet survival rather than recovery.
How can platelet refractoriness be prevented?
Transfuse patients with ABO-identical units, which are ideally from single-donors and are leukoreduced (see: TRAP trial).
