ASCP Transfusion Medicine 2 — Questions and Answers

Question 1: The most clinically significant Rh antigen after D is:

C antigen
E antigen
c antigen (little c) (Correct answer)
e antigen

Correct answer: c antigen (little c)

The c (little c) antigen is the most clinically significant Rh antigen after D. Anti-c can cause severe hemolytic transfusion reactions and HDFN, and is particularly important in sickle cell disease patients with chronic transfusion needs.

Rh system antigens in clinical order of importance: D, c, E, C, and e. The Rh antigens are polypeptides (RhCE and RhD proteins) on red cell membranes. Anti-c is IgG, clinically significant, and causes hemolytic transfusion reactions and severe HDFN. In sickle cell disease, approximately 96% of Black patients are D+C+E-c+e+ (R1r or Rr phenotype); extended phenotyping for C, E, c, e, and K is recommended before chronic transfusion programs to minimize alloimmunization.

Question 2: Cryoprecipitate is prepared from fresh frozen plasma (FFP) and is enriched for which components?

Albumin and IgG
Fibrinogen, Factor VIII, vWF, Factor XIII, and fibronectin (Correct answer)
All coagulation factors equally
Platelets and Factor V

Correct answer: Fibrinogen, Factor VIII, vWF, Factor XIII, and fibronectin

Cryoprecipitate is the cold-insoluble precipitate formed when FFP is thawed at 1–6 degrees C. It is enriched in fibrinogen (at least 150 mg per unit), Factor VIII (at least 80 IU per unit), vWF, Factor XIII, and fibronectin.

Cryoprecipitate preparation: FFP thawed slowly at 1–6 degrees C, cold-insoluble precipitate forms, supernatant plasma is removed, precipitate resuspended in 10–15 mL plasma. Contents per unit: fibrinogen at least 150 mg (typically 200–300 mg), Factor VIII at least 80 IU, vWF approximately 100 IU, Factor XIII approximately 20–30% of normal, and fibronectin. Clinical uses: fibrinogen replacement in DIC and congenital afibrinogenemia, hemophilia A when Factor VIII concentrate is unavailable, vWD type 2 or 3 when vWF concentrate is unavailable, and Factor XIII deficiency. Dose: 1–2 units per 10 kg body weight raises fibrinogen by approximately 50–100 mg/dL.

Question 3: Irradiation of blood products prevents:

Bacterial contamination
Transfusion-associated graft-versus-host disease (TA-GvHD) (Correct answer)
CMV transmission
Alloimmunization to HLA antigens

Correct answer: Transfusion-associated graft-versus-host disease (TA-GvHD)

Blood product irradiation (25 Gy to the center of the unit) inactivates donor T lymphocytes, preventing TA-GvHD in susceptible immunocompromised recipients. TA-GvHD occurs when viable donor T cells engraft and attack the immunocompromised host.

TA-GvHD occurs when donor lymphocytes proliferate in an immunocompromised host and mount immune attack against host tissues including skin, gut, liver, and bone marrow. Mortality exceeds 90%. Risk populations requiring irradiated products include congenital immunodeficiency (SCID, DiGeorge), stem cell or bone marrow transplant recipients, intrauterine transfusions, neonatal exchange transfusions, HLA-matched platelets, directed donations from blood relatives, and patients receiving fludarabine or cladribine. Irradiation does NOT prevent CMV; leukoreduction reduces CMV risk. Pathogen inactivation technologies using amotosalen+UVA or riboflavin+UV inactivate both T cells and pathogens but are not available for red cells.

Question 4: Kidd antibodies (anti-Jka, anti-Jkb) are clinically notorious because they:

Cause strong immediate hemolysis always detectable on crossmatch
Can become undetectable between transfusions, causing unexpected delayed hemolytic transfusion reactions (Correct answer)
Are only IgM and activate complement weakly
React best at room temperature

Correct answer: Can become undetectable between transfusions, causing unexpected delayed hemolytic transfusion reactions

Kidd antibodies are notorious for declining to undetectable levels between transfusions. When antigen-positive blood is transfused, a rapid anamnestic response occurs, causing a delayed hemolytic transfusion reaction (DHTR) 3–14 days later.

Kidd antigens (Jka and Jkb) are urea transporters on red cells. Kidd antibodies are IgG, complement-activating, and clinically significant. Hallmarks: titer drops to undetectable levels between transfusion episodes leading to negative antibody screen and compatible crossmatch, then antigen-positive blood transfused triggers memory B cell anamnestic response with rapidly rising anti-Jk titer. IgG anti-Jk then coats transfused cells, causing complement-mediated intravascular or extravascular hemolysis 3–14 days post-transfusion with falling hemoglobin, positive DAT, hemoglobinuria, and hyperbilirubinemia. Prevention: document all previously identified antibodies regardless of current screen result.

Question 5: Which coagulation factor is present in fresh frozen plasma (FFP) but NOT in stored packed red blood cells?

Factor VII
Factor VIII (Correct answer)
Factor X
Factor XIII

Correct answer: Factor VIII

Factor VIII is labile and rapidly degrades during storage at refrigerated temperatures. FFP stored at minus 18 degrees C or colder preserves Factor VIII. Stored RBC units contain essentially no Factor VIII. FFP contains all coagulation factors including the labile Factors V and VIII.

Coagulation factor stability in blood products: FFP (frozen within 8 hours of collection, stored at minus 18 degrees C or colder for 1 year) contains all factors including labile Factor VIII at 0.7 IU per mL minimum and Factor V. Stored RBCs at 4 degrees C for 42 days have Factor VIII activity essentially at zero (half-life approximately 12 hours, degrades rapidly). Factor V is also labile but more stable than VIII. Stable factors VII, IX, X, XI, and XIII are present in both products. FFP standard dose is 10–15 mL per kg.

Question 6: In blood banking, what additional safety check does a crossmatch provide beyond a type and screen?

It provides the patient's ABO and Rh type
It serologically tests the specific donor unit against the patient's serum to detect incompatibility (Correct answer)
It identifies all patient antibodies
It determines HLA compatibility

Correct answer: It serologically tests the specific donor unit against the patient's serum to detect incompatibility

The crossmatch tests the actual donor unit against the specific patient's serum or plasma. It serves as the final safety check for ABO compatibility (immediate spin), detection of unexpected antibodies against donor antigens (antiglobulin crossmatch), and confirms serologic compatibility before release.

Type and screen: (1) ABO and Rh typing (forward and reverse); (2) Antibody screen with 2–3 reagent screening cells. If screen is negative and no antibody history exists, electronic or computer crossmatch is sufficient: computer verifies ABO compatibility of donor unit using prior type results — no serologic test required per AABB standards if two independent ABO typings are on file. Serologic crossmatch: immediate spin detects ABO incompatibility; antiglobulin phase detects IgG antibodies against donor antigens. Indications for full serologic crossmatch include positive antibody screen, history of clinically significant antibodies, and emergency situations.

ASCP Transfusion Medicine 2

The most clinically significant Rh antigen after D is: