4.3 Blood Components, Preparation & Storage

Blood Component Preparation

Modern transfusion medicine relies almost entirely on component therapy—transfusing only the specific portion of the blood that the patient needs, rather than whole blood. This targeted approach maximizes the utilization of a single donation, prevents circulatory overload in the recipient, and ensures the optimal storage conditions for each specific element. Whole blood is separated into its primary components through heavy centrifugation based on the specific gravity of the blood elements.

The Separation Process:

1. First Centrifugation (Soft Spin): Whole blood is centrifuged at a low speed. This separates the heavy red blood cells (which settle at the bottom) from the platelet-rich plasma (PRP) at the top.
2. Second Centrifugation (Hard Spin): The PRP is expressed into a satellite bag and centrifuged at a high speed. This packs the platelets to the bottom, leaving platelet-poor plasma (which is frozen as Fresh Frozen Plasma, FFP) at the top.

Anticoagulants and Preservative Solutions

When blood is collected, it is drawn into a primary bag containing a precise volume of an anticoagulant-preservative solution. This solution prevents clotting during collection and provides nutrients to maintain RBC viability, ATP levels, and 2,3-DPG function during long-term storage. The specific formulation dictates the maximum storage time (shelf life) of the red cells.

Common Anticoagulant-Preservatives:

• CPD (Citrate-Phosphate-Dextrose): Citrate chelates calcium to prevent the coagulation cascade. Phosphate acts as a buffer to maintain pH. Dextrose provides a carbohydrate source for ATP generation via glycolysis. Shelf life: 21 days.
• CP2D (Citrate-Phosphate-Double Dextrose): Contains twice the dextrose of CPD, providing a greater energy reserve. Shelf life: 21 days.
• CPDA-1 (Citrate-Phosphate-Dextrose-Adenine): Adenine is a crucial addition. It provides a substrate for the RBC to synthesize more adenosine triphosphate (ATP), significantly extending viability. Shelf life: 35 days.

Additive Solutions (AS): To further extend shelf life and reduce the viscosity of packed red cells (making them flow easier during rapid transfusion), additive solutions (e.g., AS-1/Adsol, AS-3/Nutricel, AS-5/Optisol) are heavily utilized. These are located in a satellite bag and are added directly to the packed red cells after the plasma has been removed. They provide additional dextrose, adenine, and saline (and sometimes mannitol to reduce hemolysis).

• RBCs stored in Additive Solutions: Shelf life: 42 days.

Storage Lesions

During prolonged storage at 1-6°C, red blood cells undergo biochemical and biomechanical changes collectively known as "storage lesions."

• Decreased: ATP (loss of membrane integrity), 2,3-DPG (shifting the oxygen dissociation curve to the left, meaning RBCs hold onto oxygen tighter and release less to tissues), pH (due to lactic acid buildup).
• Increased: Extracellular potassium (due to failure of the Na+/K+ pump), plasma hemoglobin (due to slow hemolysis). Due to the high potassium, neonates and massive transfusion patients often require fresher blood (e.g., <7 days old) to prevent cardiac arrhythmias.

Storage Conditions and Shelf Life

Maintaining strict temperature control is paramount. Deviations compromise component viability, accelerate storage lesions, and drastically increase the risk of dangerous bacterial proliferation.

Packed Red Blood Cells (PRBCs)

• Storage Temperature: 1°C to 6°C in continuously monitored refrigerators.
• Transport Temperature: 1°C to 10°C.
• Shelf Life: 35 days (CPDA-1) or 42 days (AS).
• Indications: Symptomatic anemia, acute blood loss, sickle cell crisis.

Fresh Frozen Plasma (FFP)

FFP must be separated from whole blood and rapidly frozen at ≤-18°C within 8 hours of collection. This rapid freezing is critical to preserve the labile coagulation factors (Factor V and Factor VIII), which degrade quickly at warmer temperatures.

• Storage Temperature: ≤ -18°C (or ≤ -65°C).
• Shelf Life: 1 year at -18°C, or 7 years at -65°C.
• Thawing: Thawed at 30-37°C in an FDA-approved water bath or dry incubator.
• Post-Thaw Storage: Once thawed, it must be stored at 1°C to 6°C and transfused within 24 hours. If not used, it can be relabeled as Thawed Plasma (usable for up to 5 days, though Factor V and VIII levels decline significantly).
• Indications: Multiple coagulation factor deficiencies (e.g., DIC, liver disease), massive transfusion protocols, reversal of warfarin toxicity.

Platelets (Random Donor and Apheresis)

• Storage Temperature: 20°C to 24°C (controlled room temperature).
• Requirement: Must maintain continuous gentle agitation on a platelet rocker or agitator. This prevents the platelets from aggregating and facilitates critical gas exchange (oxygen in, carbon dioxide out) across the breathable plastic bag membrane, preventing a lethal drop in pH.
• Shelf Life: 5 days from collection. Due to room temperature storage, platelets carry the absolute highest risk of bacterial contamination among all blood components. Rigorous bacterial screening (using culture methods) is mandatory before release.
• Indications: Severe thrombocytopenia, qualitative platelet defects, massive hemorrhage.

Cryoprecipitated AHF (Cryo)

Prepared by thawing FFP slowly at 1-6°C. A dense, white precipitate forms at the bottom of the bag. The supernatant plasma is expressed, and the precipitate is refrozen. Cryo is heavily concentrated with Fibrinogen, Factor VIII, Factor XIII, and von Willebrand Factor.

• Storage Temperature: ≤ -18°C.
• Shelf Life: 1 year.
• Post-Thaw: Thawed at 37°C. Once thawed, it must be kept at room temperature (20-24°C) and transfused within 6 hours (or 4 hours if multiple units are pooled in an open system).

Special Component Modifications and Advanced Technologies