Transfusion Medicine: Components, Thresholds, and Adverse Reactions
The transfusion medicine section tests component selection and storage, transfusion thresholds, recognition of adverse reactions, and patient blood management.
Components and storage
Red cells are stored at 1–6 °C for 42 days in additive solution (AS-1, AS-3, AS-5) or 35 days in CPDA-1. Platelets are held at 20–24 °C with continuous agitation for 5 days. Plasma is frozen at ≤−18 °C for up to 12 months, then kept at 1–6 °C for 24 hours after thawing. Leukoreduction reduces residual white cells below 5 × 10^6 per unit; irradiation (25 Gy to the center, 15 Gy minimum) prevents transfusion-associated GVHD in at-risk recipients; washing removes plasma protein for IgA-deficient or severe allergic recipients.
Indications
Restrictive red cell thresholds (7 g/dL, and 8 g/dL in cardiac surgery and some orthopedic and ICU settings) are supported by trials; give a single unit and reassess. Prophylactic platelets are typically given below 10 × 10^9/L in stable patients, with higher thresholds before procedures.
Reactions
Febrile nonhemolytic and allergic reactions are most common. Acute hemolytic reactions reflect ABO error and present with fever, hypotension, hemoglobinuria, and DIC. TRALI occurs within 6 hours with bilateral infiltrates and no volume overload; TACO presents with hypertension, JVD, and elevated BNP and responds to diuretics. Delayed hemolytic reactions appear at days 3–14 with a falling hemoglobin and positive DAT.
Worked example
A patient develops dyspnea, blood pressure 170/95, JVD, and BNP 900 within two hours of one unit. TRALI is typically hypotensive and afebrile without volume overload, so this is TACO: stop the transfusion, sit the patient upright, give oxygen and diuretics, and report the reaction.
Traps that cost marks
Treating group O as universally compatible - O red cells are, but group O plasma carries anti-A and anti-B, so AB plasma is the universal plasma choice. Assuming irradiation prevents TACO or TRALI. Ignoring a positive DAT after transfusion.