Blood Components and Transfusion — Products, Storage, Massive Transfusion and Reactions

Donated whole blood is usually divided into component parts for ease of storage and administration. The three classic components are red blood cells, platelets (thrombocytes) and plasma. Plasma can be fractionated further into cryoprecipitate (cryoprecipitated antihemophilic factor) and clotting-factor concentrates of variable purity. Because modern practice replaces only what the patient lacks, current indications for whole blood are limited.

The aims of transfusion are to raise haemoglobin and tissue oxygenation, maintain blood volume (preventing ischaemia and hypovolaemic shock), and restore platelets, coagulation factors and other plasma proteins to a functional state. Giving the right component also avoids unnecessary volume and unnecessary exposure to donor antigens.

After processing, blood is stored at an appropriate temperature, often between +2 °C and +6 °C. Platelets and fresh frozen plasma (FFP) must be prepared within 8 hours of collection. Platelets are kept at room temperature with agitation, typically for 5 days unless shelf-life-extending methods are used. Depending on national regulations, FFP can be stored at −18 °C for 1 year, −25 °C for 36 months or −65 °C for up to 7 years.

Guidelines from the American Association of Blood Banks favour a restrictive approach in non-haemorrhagic anaemia. Older practice used a liberal cut-off of haemoglobin below 10 g/dL; current guidelines generally use 7.0 g/dL for asymptomatic healthy patients, with higher thresholds of 7.5 g/dL for coronary artery disease and 8 g/dL for orthopaedic surgery. The 7 g/dL threshold is also acceptable in gastrointestinal bleeding and critically ill patients.

• Unless the patient is actively bleeding, transfuse one unit at a time; one unit of packed red cells typically raises haemoglobin by about 1 g/dL and haematocrit by about 3%.
• Check the post-transfusion haemoglobin before giving more.
• In haemorrhagic shock, treatment follows a massive transfusion protocol rather than a haemoglobin trigger.
• Because citrate preserves packed cells, a calcium-containing fluid in the same line can clot the line — prime with normal saline.

Platelets. Transfusion is mainly indicated to treat or prevent bleeding in thrombocytopenia or platelet function disorders. For active bleeding, StatPearls lists thresholds of below 50,000/µL with severe bleeding (including DIC), below 30,000/µL when bleeding is not severe, and below 100,000/µL in multiple trauma or intracranial bleeding. For prophylaxis in bone marrow failure, transfuse when the count is below 10 × 10⁹/L (20 × 10⁹/L if other bleeding risk factors exist); above 50 × 10⁹/L is needed before invasive procedures.

Fresh frozen plasma. FFP is the liquid portion of a unit of whole blood frozen within 8 hours. It contains all coagulation factors except platelets, plus fibrinogen (400–900 mg per unit), albumin, protein C, protein S and antithrombin, and is free of red cells and leukocytes. A standard dose is 10–20 mL/kg (4–6 units in adults), raising factor levels by about 20%. Indications include liver disease, DIC, massive transfusion, cardiopulmonary bypass and TTP.

Cryoprecipitate is derived from plasma. It supplies fibrinogen in acquired coagulopathies such as DIC and in trauma or childbirth, and can be used in emergencies for von Willebrand disease and haemophilia A only when specific concentrates are unavailable.

Massive transfusion is traditionally the administration of 10 or more units of whole blood or packed red cells within 24 hours — roughly one adult blood volume. The definition is arbitrary, and some definitions use more than 20 units over 24–48 hours, so clinicians also look at the rate of bleeding. The goal is to prevent death from hypoperfusion while surgery or intervention achieves haemostasis.

• Balanced products: resuscitate with a 1:1:1 ratio of red cells, plasma and platelets (some protocols use 2:1:1) or whole blood instead of crystalloid-heavy resuscitation, which reduces dilutional coagulopathy.
• Tranexamic acid early, particularly within 3 hours of injury, because trauma disturbs fibrinolysis.
• Calcium chloride or gluconate for hypocalcaemia caused by citrate in stored products.
• Warm all products to prevent hypothermia.
• Monitor ABG, lactate, ionised calcium, potassium, PT/INR, aPTT, fibrinogen and TEG/ROTEM every 30–60 minutes or per protocol.
• Define deactivation criteria (haemodynamic stability, bleeding control, normal labs) so that blood is not over-transfused.

Reactions are first sorted by timing. Acute reactions occur during or within 24 hours of transfusion; delayed reactions appear later. The commonest reactions are fever and non-severe allergic reactions (rash, urticaria, pruritus), which together account for roughly 70–80% of adverse events. About 7% are severe, with respiratory distress, hypotension, reduced consciousness or haemoglobinuria. Severe reactions appear at a median of about 20 minutes, non-severe at about 100 minutes, so observe patients closely for the first 2 hours.

Both present with breathlessness after transfusion, and both are favourite exam contrasts. TRALI is diagnosed when symptoms develop during or within 6 hours of transfusion in a patient without other risk factors for acute lung injury (sepsis, aspiration, shock). The picture is fever, hypotension, tachycardia, bilateral exudative infiltrates, no evidence of vascular overload and hypoxaemia (SpO₂ below 90% on room air or PaO₂/FiO₂ below 300 mmHg). It follows a two-hit hypothesis: donor antibodies (HNA or HLA) plus recipient neutrophil priming cause capillary leak. Plasma from female donors with a history of pregnancy is a recognised risk. Delayed TRALI occurs 6–72 hours after transfusion and carries higher mortality.

TACO reflects circulatory overload: risk factors are cardiac failure, renal failure, positive fluid balance, advanced age and rapid transfusion. Supportive features are raised BNP, raised central venous pressure, evidence of left heart failure, pulmonary oedema on X-ray and a positive fluid balance. Treat with diuretics and oxygen; TRALI needs supportive respiratory care and the implicated donor products quarantined.

1. Stop the transfusion immediately, keep the intravenous line open with saline and assess airway, breathing and circulation.
2. Recheck patient and bag identity; return the bag and giving set to the blood bank for retesting, and send a fresh patient sample.
3. Send direct and indirect antiglobulin (Coombs) tests, measure free haemoglobin to look for haemolysis and take blood cultures from the patient and the bag to exclude sepsis.
4. Treat by severity: for mild urticaria give an antihistamine (25–50 mg diphenhydramine in StatPearls) and resume only if symptoms resolve with no breathlessness or hypotension; for anaphylaxis give intramuscular adrenaline (epinephrine) with oxygen, fluids and corticosteroids.
5. For haemolysis support circulation and urine output; for TACO give diuretics and oxygen.

The blood bank confirms the patient's ABO and Rh group, performs an antibody screen and a crossmatch with the donor unit before issuing blood. Group-specific platelets are generally recommended, but cross-group platelets may be used in emergencies such as traumatic bleeding. Serological crossmatching is rarely required for platelets unless the concentrate contains many red cells.

False-positive results of testing can arise from rouleaux formation, antibodies passively transferred by platelet transfusion or intravenous immunoglobulin, and reagent preservatives. Technical errors or antibodies showing a dosage effect can cause false negatives. Throughout, the AABB advises that a blood filter should not be used for more than 4 hours, because of the risk of bacterial growth.