Blood Transfusion — Products, Indications & Reactions

The Concept — WHY We Use Components

Modern practice almost never transfuses whole blood. Instead a single donation is separated into components, for two good reasons: one donation can then treat several different patients, and each patient receives only the part they actually need, avoiding the risks of the rest. Understanding what each component contains tells you exactly when to use it.

Blood Components & Their Uses

Indications — a Restrictive Approach

Because transfusion carries real risks, a restrictive threshold is used: red cells are generally given when haemoglobin falls below about 7 g/dL (a slightly higher trigger of ~8 g/dL in patients with cardiac disease), or in acute blood loss causing haemodynamic compromise. The decision rests on the patient's symptoms and physiology, not the number alone.

Grouping & Cross-matching — the Safety Step

Every transfusion must be ABO and Rhesus (Rh) compatible. Group O negative is the universal donor (no A, B or Rh antigens to react against) and is used in dire emergencies; AB positive is the universal recipient. Before a routine transfusion, the patient's serum is cross-matched against the donor cells to detect any incompatibility. The commonest cause of a fatal reaction is a clerical error — the wrong unit given to the wrong patient — which is why bedside identity checks are non-negotiable.

Transfusion Reactions — Classified BY Timing

It helps to think of reactions as immediate or delayed:

• Acute haemolytic reaction (the most dangerous) — usually ABO incompatibility from a clerical error. Recipient antibodies destroy the donor cells (intravascular haemolysis), causing fever, loin/back pain, hypotension, haemoglobinuria, DIC and acute renal failure. Stop the transfusion immediately.
• Febrile non-haemolytic reaction — recipient antibodies against donor white-cell antigens cause fever and chills; common and benign (reduced by leucodepletion).
• Allergic / urticarial — a reaction to donor plasma proteins; ranges from urticaria to anaphylaxis (classically in IgA-deficient recipients).
• TACO (transfusion-associated circulatory overload) — too much volume too fast → pulmonary oedema, especially in the elderly/cardiac patient.
• TRALI (transfusion-related acute lung injury) — donor antibodies trigger acute lung injury with hypoxia and pulmonary infiltrates.
• Delayed — delayed haemolytic reaction (days later), infection transmission (hepatitis B/C, HIV — now very rare with screening), and iron overload with repeated transfusion.

Managing a Suspected Reaction

The immediate steps are the same whatever the cause: stop the transfusion, keep the IV line open with saline, re-check the patient's and unit's identity, and resuscitate (oxygen, fluids, support blood pressure). Then treat specifically — for a severe acute haemolytic reaction, maintain urine output and manage DIC and renal failure — and report the reaction, returning the unit and a fresh sample to the blood bank for investigation.

Changes in Stored Blood (WHY Fresh Differs)

Understanding what happens to blood during storage explains several transfusion complications. Over its storage life, red cells progressively leak potassium (so stored blood is potassium-rich), 2,3-DPG falls (temporarily reducing oxygen offloading), platelets and clotting factors degrade (so stored blood does not correct coagulopathy), the blood becomes acidic and cold, and microaggregates form. These changes underlie the complications of massive transfusion.

Autologous Transfusion

A patient can sometimes receive their own blood — collected pre-operatively (predeposit), salvaged and returned during surgery ('cell salvage'), or by haemodilution. This eliminates the risks of incompatibility and transmitted infection, which is its main appeal, though it is not suitable in cancer or infected fields.

Principles of Safe Transfusion

Because the deadliest reactions come from giving the wrong blood to the wrong patient (a clerical error), safety rests on rigorous checks: correct sample labelling at the bedside, formal group-and-cross-match, and a final bedside identity check of patient and unit by two people before starting. The transfusion is observed closely, especially in the first 15 minutes when severe reactions declare themselves.

Most fatal reactions arise from clerical error, not immunology.

• Component therapy: one donation treats several patients, each getting only what they need.
• Packed cells (anaemia, 1 unit ≈ +1 g/dL Hb), FFP (clotting factors), platelets (thrombocytopenia + bleeding), cryoprecipitate (fibrinogen).
• Restrictive trigger ≈ Hb <7 g/dL (<8 in cardiac disease); O-negative = universal donor, AB-positive = universal recipient; always cross-match.
• Acute haemolytic reaction (ABO incompatibility, usually clerical error) is the most dangerous — fever, loin pain, haemoglobinuria, DIC, renal failure; stop the transfusion.
• Also: febrile non-haemolytic, allergic/anaphylaxis, TACO (overload), TRALI (lung injury), infection. First step for any reaction = stop transfusion, saline, recheck identity, resuscitate, report.