Blood Typing and RBC Transfusions

Question 1

Describe ABO blood testing.

Answer 1

• ABO blood group–O, A, B, or AB carbohydrates on RBCs, and naturally-occurring IgM anti-A and/or anti-B in persons without the antigen(s)
• Anti-A and anti-B can be strongly hemolytic to transfused RBCs with group B or A antigens, respectively
• RBC transfusions must be ABO-compatible to avoid potentially fatal transfusion reactions

Question 2

What is the Rh(D) blood group?

Answer 2

• RBC Rh proteins type D+ or D-negative
• Hemolytic anti-D is not naturally occurring, but is readily induced in D-negative persons by transfusion of D+ RBCs
• Thus, D-negative patients should receive D-negative RBCs whenever possible, barring shortage or emergency

Question 3

What is the RBC antibody screen?

Answer 3

• Potentially hemolytic RBC alloantibodies to Rh, Kell, Kidd, Duffy and other blood group antigens can be induced by transfusion or pregnancy (exposure to fetal RBCs)
• Before RBC transfusion, the patient’s plasma is tested against reagent RBCs for these IgG antibodies
• Potentially hemolytic RBC antibodies are found in 1-2% of all patients, and 5-20% of multiply transfused patients

Question 4

What is crossmatching?

Answer 4

• ABO- and Rh(D)-compatible donor RBC units are identified and designated for the patient
• If the patient has hemolytic RBC antibodies (e.g., anti-K, Kell blood group), antigen-negative (e.g., K-negative) RBC units are sought by typing, and the plasma is crossmatched for IgG antibody vs the donor RBCs

Question 5

What are “type-and-sceen” orders and “type-and-cross” orders?

Answer 5

• “Type-and-screen” orders have the ABO and Rh(D) blood type and the antibody screen performed
  
  • If the screen is negative, ABO and Rh(D)- matched RBC units can be crossmatched rapidly if needed (e.g., a surgical procedure which requires transfusion infrequently)
• “Type-and-cross” orders include the type, screen, and crossmatching of designated RBC units, for patients likely to need transfusion

Question 6

What is the direct antiglobulin test (DAT) (direct Coombs test)?

Answer 6

• The DAT detects IgG or complement C3 on RBCs
• Not routinely done in all compatibility test specimens
• Reactive DATs are seen with RBC autoantibodies, hemolytic transfusion reactions, and drug-dependent antibodies on RBCs

Question 7

How long does blood compatibility testing take and what are the procedures for emergency type O?

Answer 7

• On a stat basis, the entire set of compatibility tests takes 45-60 min if no problems are found
  
  • For antibody problems, resolution and crossmatching of compatible RBC units takes from 2-3 hr for a simple antibody to a day or more in highly difficult cases
• Emergency uncrossmatched group O RBCs can be requested by the physician if medically necessary
  
  • These RBCs should also be Rh(D)-negative in girls and women of childbearing age, to avoid later anti-D hemolytic disease of the fetus and newborn
  • Risk: frequency of hemolytic RBC antibodies

Question 8

What types of patients require specialized, rare RBC units?

Answer 8

• A few patients require rare RBC units to avoid hemolytic transfusion reactions
• They have:
  
  • multiple RBC antibodies such that only a few units are negative for all of the target antigens
  • an antibody to a highly common antigen
• The latter category might have siblings as potential blood donors, with the same autosomal-recessive antigen-negative status
  
  • anti-U in the MNSs blood group (1-2% of African-American donors compatible)
  • anti-H in the Bombay ABO-variant blood group (<1:300,000 US donors compatible)
• Rare RBC units are obtained from community blood centers who search and share nationally if needed
  
  • these units may be frozen for <10 years

Question 9

How are blood-bank specimens collected and administered?

Answer 9

• Before collection of blood-bank or other laboratory specimens, the patient’s identity must be confirmed with the facility wristband and if possible, the patient
  
  • All specimens should be labeled immediately at the bedside with the patient’s name and at least one other patient identifier (medical record number, birthdate)
• If the patient has been transfused or pregnant in the past three months, a fresh specimen must be tested every three days to rule out newly developing RBC alloantibodies
  
  • Specimens collected on day zero (e.g., Friday anytime) expire at the end of day 3 (e.g., Monday at 1159pm).
• Administration of all blood components should be performed as a “time-out” procedure

Question 10

What is the verification process for blood transfusion?

Answer 10

• Verification is a three-way process:
  
  • the blood bag label with the unit number and blood type
  • the patient’s identity, confirmed by the facility wristband and if possible, the patient
  • the transfusion tag applied on the unit by the blood bank, linking the unit number and the intended recipient
  • some hospitals have an extra blood bank wristband code
  • two providers must cross-check the patient and blood-unit information together at the bedside before transfusion, unless the hospital has a bedside computerized barcode-reader system for verification by one provider

Question 11

How much is one units of blood, and what is the patient response to one unit?

Answer 11

• One RBC unit: 180 mL RBCs, 30 mL plasma, 100 mL preservative
  
  • Stored at 1-6°C for <6 weeks
• Average patient’s laboratory response to one unit: 1 gm/dL rise in Hgb

Question 12

What is the management of acute bleeding in terms of transfusion?

Answer 12

• In acute bleeding, intravenous fluid replacement is the initial priority, to avoid hypovolemia and hypoperfusion
  
  • The adult blood volume is 70 mL/kg body weight
  • RBC transfusions are usually needed when blood loss reaches >30% of blood volume (1500 mL average)
• Massive transfusion is defined as >1 blood volume of RBCs transfused, or about 10 units in an average adult
  
  • Recent military trauma experience suggests that in massive transfusions, one unit of plasma should be given per unit of RBCs, to maintain clotting factor levels
  • Platelets should also be given

Question 13

What is the role of blood transfusion in low-production anemia?

Answer 13

• The underlying cause of anemia should be diagnosed and treated in lieu of transfusion whenever possible; e.g., deficiencies of erythropoietin, iron, folic acid, vitamin B12
• Patients with hemoglobin (Hgb) levels <5 gm/dL, even when previously healthy, have increased risk for anemia-associated complications or death—based partly on observations of Jehovah’s Witnesses who refuse RBC transfusions due to religious convictions.
• Patients with good cardiopulmonary reserves can have a transfusion hemoglobin (Hgb) threshold of 6-7 gm/dL
  
  • ​However, patients with longstanding severe anemia must be transfused carefully under close observation, due to risk of transfusion-associated circulatory overload (TACO)
• For patients with acute cardiac disease, Hgb levels >8 gm/dL have been suggested
• For other patients with reduced cardiopulmonary reserves and signs or symptoms of anemia, transfusion thresholds of 7-8 gm/dL are often applied, depending on the patient’s degree of disease and signs or symptoms of anemia
• Transfusing RBCs one unit at a time with evaluation before the next unit is suggested in non-acute patients

Question 14

What is the postoperative role of blood transfusion?

Answer 14

• Blood management refers to the concept of comprehensive individualized perioperative evaluation and therapy designed to minimize blood component transfusion in surgical patients:
  
  • advance diagnosis and treatment of anemia and coagulopathies
  • hemostatic surgical techniques
  • recovery and infusion of shed RBCs from sterile tumor-free surgical fields when feasible
  • and conservative peri- and postoperative transfusion practices
• In selected patients with sufficient lead time, erythropoietin therapy with iron supplementation may be useful
• Preoperative autologous RBC donations can be counterproductive for blood management, as they may cause preoperative anemia
  
  • However, such units may be very helpful in patients with antibody difficulties in crossmatching
  • If collected, maximal lead time (3-6 weeks) is recommended to permit Hgb recovery and a net gain in RBC mass available inside and outside the patient