Choosing the Right Blood Component

Transfusion replaces a specific deficit: oxygen carrying capacity (red cells), primary haemostasis (platelets), coagulation factors (plasma) or fibrinogen (cryoprecipitate and fibrinogen concentrate). Each product corrects one defect, carries its own risks and follows its own compatibility rules. Choosing the wrong product is a common source of harm and waste, and giving blood when a non-blood treatment would work exposes the patient to avoidable risk.

Whole blood and components. Most donations are separated into components so that one donation can serve several patients. Whole blood is used mainly in major haemorrhage and where component separation is unavailable. Granulocytes are rarely used.

What each product supplies.

• Red cells: haemoglobin; a unit is usually about 250 to 350 mL.

• Platelets: an adult therapeutic dose is one apheresis unit or a pool of whole blood derived units, in about 150 to 300 mL.

• Plasma: all coagulation factors and natural anticoagulants; a unit is usually about 200 to 300 mL.

• Cryoprecipitate: fibrinogen, factor VIII, von Willebrand factor, factor XIII and fibronectin in a small volume.

Risk context. Serious risks are transfusion associated circulatory overload, transfusion related acute lung injury, haemolytic reactions from identification errors, bacterial contamination (highest with platelets because they are stored at room temperature), alloimmunisation and, with repeated red cell transfusion, iron overload. Transmitted infection is now rare where donor screening is reliable, but residual risk is higher where screening capacity is limited.

Special groups. Neonates, children, pregnant women, patients with sickle cell disease and patients with cardiac or renal failure need product specifications or doses that differ from adults. In East Africa, availability of platelets, plasma, cryoprecipitate and fibrinogen concentrate is often limited, so red cells or whole blood may be the only product available, and the plan must state what will be done if the ideal product cannot be obtained.

Define the defect first. Ask whether the problem is oxygen delivery, platelet number or function, factor deficiency or low fibrinogen. Confirm with haemoglobin, platelet count, prothrombin time, activated partial thromboplastin time and Clauss fibrinogen, and with viscoelastic testing where available. In active bleeding, laboratory results lag behind the patient, so decisions rest on bleeding rate, haemodynamics and the likely trajectory.

Matching defect to product.

Representative thresholds. These vary by setting and are never universal orders. Red cells: about 7 g/dL in stable hospitalised adults, with higher values in selected cardiac and orthopaedic settings. Platelets: under 10 x 10⁹/L for prophylaxis in stable hypoproliferative thrombocytopenia (higher with fever or sepsis), over 50 x 10⁹/L for active bleeding or major surgery, and over 100 x 10⁹/L for central nervous system or ocular bleeding. Fibrinogen: over 1.5 g/L in bleeding and over 2 g/L in postpartum haemorrhage.

Red flags that change the plan. Ongoing haemorrhage, haemodynamic instability, a positive antibody screen, a history of reactions, pregnancy, and a need for irradiated, washed or antigen negative products.

Sequence of decisions.

1. Confirm the indication and exclude a non-blood alternative.

2. Choose the product that corrects the defect.

3. State special requirements: irradiated, cytomegalovirus safe, washed, antigen negative or neonatal grade.

4. State the dose and rate, adjusted for weight and cardiac reserve.

5. State urgency: emergency (minutes), urgent (within hours) or routine.

6. State the reassessment time and the clinical or laboratory endpoint.

7. Confirm consent and document the rationale.

Usual adult starting doses.

• Red cells without ongoing bleeding: one unit, then reassess before any further unit.

• Platelets: one adult therapeutic dose.

• Plasma: 10 to 15 mL/kg, about 3 to 4 units in a 70 kg adult.

• Cryoprecipitate: two pools, about 10 single donor units, with an expected fibrinogen rise of roughly 1 g/L.

• Fibrinogen concentrate: dose calculated from current fibrinogen, target and body weight using the product specification.

Compatibility. Red cells, plasma and platelets each have separate ABO and RhD rules. Order the group of the recipient, never assume one rule fits all products.

If the ideal product is unavailable. State the fallback in advance: for example whole blood or red cells with early antifibrinolytic therapy in haemorrhage, and escalation to the blood bank medical lead.

Monitoring. Baseline and repeated vital signs, response in the relevant test (haemoglobin, platelet count, fibrinogen, prothrombin time), and bleeding control. Reassess after each unit in non-bleeding patients.

Complications. Reactions, overload, infection, alloimmunisation and metabolic effects in massive transfusion. Any new fever, dyspnoea, rigors or hypotension during or within 24 hours of a transfusion requires immediate stopping and assessment.

Referral and escalation. Involve the haematologist or transfusion medicine specialist for refractory thrombocytopenia, antibodies, complex product requirements and recurrent reactions. Involve the blood bank early in any bleeding patient.

Disposition. Document product, volume, response and any reaction. Decide whether further transfusion is needed or the underlying cause needs treatment so that dependence on transfusion is avoided.