Blood transfusion

Red Blood Cells

Group & Screen and Crossmatch

• ABO blood type (O, A, B, or AB)
  • Most important antigen group
• RhD group (positive or negative)
  • Second most important antigen group
• There are more than 30 minor blood group antigens, including Kell (K and k), Kidd (Jk^a^ and Jk^b^), Duffy (Fy^a^ and Fy^b^) and MNS (S and s)
• Group and screen
  • Group tests recipient for ABO and RhD status
  • Screen tests the recipient plasma for unexpected and clinically significant minor antigen incompatibility
  • Takes about 45 minutes, but if the screen is positive then can take days to determine which specific antibodies are causing the problem
• Crossmatch confirms that a specific unit of RBCs is safe to give to the recipient
  • If screen was negative, an abbreviated crossmatch is done either as immediate spin or as electronic
  • If screen was positive, then a full antiglobulin crossmatch is done

Basics

• Each unit is about 300 mL with a hematocrit of 65 to 70%, and raises the recipient's hemoglobin by about 10 g/L
• Usually transfused over 2 hours
  • Can do up to 3 or 3.5 hours in elderly over 70 years old, heart failure, LV dysfunction, prior MI, renal dysfunction, or volume overload (usually with concurrent diuretics at the start of the transfusion)

Indications

• Acute blood loss
  • Maintain hemoglobin above 70 g/L during active bleeding
  • Maintain hemoglobin higher (e.g. above 80 g/L) during active bleeding in patients with:
    • Unstable or acute coronary syndrome
    • Coronary artery disease
    • Uncontrolled or unpredictable bleeding
• Anemia
  • Consider for hemoglobin below 70 g/L in stable patients
  • Consider for hemoglobin below 80 g/L in patients undergoing orthopedic or cardiac surgery or with cardiovascular disease

Platelets

• Caution in prothrombotic thrombocytopenia syndromes like HIT, TTP, and catastrophic antiphospholipid syndrome
• Of limited utility in ITP

Indications

• In non-immune thrombocytopenia, it is reasonable to maintain platelets over 10
• For procedures with low risk of blood loss (e.g. appendectomy, cholecystectomy, vaginal delivery)
  • Platelets less than 20: transfuse 1 dose
  • Platelets 20 to 50: transfuse 1 dose if significant bleeding occurs
• For procedures with high risk of blood loss, transfuse 1 dose for platelets less than 50
• For neurosurgery, ophthalmologic procedures, or significant head trauma with high risk of intracranial hemorrhage, maintain platelets above 100 (may need multiple doses)
• For bleeding from platelet dysfunction (e.g. post-cardiopulmonary bypass, or congenital platelet defect), transfusion may be required regardless of platelet count

Plasma

• Each unit has a volume of 250 mL and requires 30 minutes to thaw
• It must be ABO compatible
• The usual dose is 10 to 15 mL/kg (3 to 4 units for average human)
• Units are transfused over 30 minutes to 2 hours (maximum 3.5 hours)
• A single dose (10 to 15 mL/kg) should normalize the INR and PTT if within 1.3 to 1.8 times normal, and lasts 6 hours (the half-life of factor VII)

Indications

• Before a procedure or during active bleeding where the INR, PT, or PTT is at least 1.8 times normal, and no other therapies are available
• During massive transfusion protocols (6 to 10 units of RBCs expected within 6 hours)
• Before a procedure or during active bleeding in patients with severe liver disease and INR greater than 2 times normal
• Not useful when INR less than 1.8, when used 1:1 with RBCs, if there is no pending surgery or bleeding, for the reversal of warfarin, for the reversal of other anticoagulants, or as nutritional support