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Blood Bank

Stored Products

This section covers what actually happens to blood components while they are sitting in storage under their required conditions (temperature, anticoagulant/additive). These changes, often collectively referred to as the “storage lesion” (especially for Red Blood Cells), are the reason components have expiration dates. Understanding these properties is key to appreciating why storage conditions are so strict and how a unit might function upon transfusion

Red Blood Cells (RBCs) - Stored at 1-6°C

RBCs undergo the most significant and well-studied changes during liquid storage. The goal of anticoagulant-preservative and additive solutions is to slow down these changes, but they cannot stop them entirely

  • Metabolic Changes
    • Decreased ATP (Adenosine Triphosphate): RBCs need ATP for energy, primarily to maintain ion pumps (like the Na+/K+ pump) and preserve their shape and flexibility. As ATP levels fall during storage, these functions decline. Additives like adenine help RBCs regenerate some ATP, extending shelf life
    • Decreased 2,3-Diphosphoglycerate (2,3-DPG): This molecule is crucial for hemoglobin’s ability to release oxygen to tissues. 2,3-DPG levels drop significantly within the first 1-2 weeks of storage
      • Implication: Immediately after transfusion of older stored RBCs, the cells may have higher oxygen affinity (hold onto O₂ more tightly) until the recipient’s body helps restore 2,3-DPG levels (usually within 24 hours). This is generally not considered clinically significant except possibly in massive transfusions or specific patient populations (e.g., neonates)
    • Decreased pH: Anaerobic glycolysis (how RBCs make ATP) produces lactic acid, causing the pH inside the unit to gradually decrease (become more acidic). A lower pH further inhibits glycolysis and affects cell function. Buffers (like phosphate) help mitigate this
  • Biochemical Changes (Membrane Integrity & Environment)
    • Increased Extracellular Potassium (K+): As the ATP-dependent Na+/K+ pump fails, potassium leaks out of the RBCs into the surrounding plasma/additive solution. Sodium leaks in
      • Implication: The supernatant (liquid portion) of older RBC units can have high potassium levels. This is a concern primarily in rapid, large-volume transfusions (especially in neonates or patients with renal impairment) where the recipient might experience hyperkalemia. Washing RBCs can remove this excess potassium
    • Increased Free Hemoglobin: Some RBCs lyse (break open) during storage due to membrane damage. This releases free hemoglobin into the supernatant. Visible hemolysis (pink/red supernatant) is a sign of unacceptable damage, and the unit should not be transfused. Standards set limits on acceptable hemolysis levels at expiration
  • Morphological Changes (Shape & Flexibility)
    • Shape Transformation: RBCs progressively lose their normal biconcave disc shape, becoming echinocytes (spiculated) and eventually spherocytes (smaller, denser spheres)
    • Decreased Deformability: These shape changes, along with membrane alterations, make the RBCs more rigid and less able to squeeze through tiny capillaries
      • Implication: Less deformable cells are cleared more rapidly from the recipient’s circulation after transfusion. Expiration dates are set to ensure that at least 75% of transfused RBCs are still circulating 24 hours post-transfusion (a measure of viability)
  • Other Changes
    • Formation of Microparticles/Microvesicles: Small fragments bud off the RBC membrane during storage. Their clinical significance is still under investigation but may relate to inflammation or thrombosis
    • Oxidative Damage: RBCs experience oxidative stress during storage, which can damage lipids and proteins

Platelets - Stored at 20-24°C with Agitation

Platelet storage presents different challenges due to the room temperature requirement

  • Metabolic Activity & pH: Platelets are metabolically active at room temperature. They consume glucose and produce lactic acid, causing the pH to drop. If the pH falls too low (e.g., below 6.2), platelet viability and function are irreversibly lost
    • Implication: Agitation is crucial for gas exchange (allowing CO₂ out, O₂ in) which helps buffer the pH. Plasma or Platelet Additive Solutions (PAS) provide buffering capacity. Shelf life (typically 5-7 days) is limited partly by the ability to maintain adequate pH
  • Activation & Function: Some degree of platelet activation occurs during storage. While they should remain functional, their effectiveness may decrease over the storage period. Loss of the characteristic “swirling” phenomenon (a light-scattering effect seen in viable, discoid platelets) indicates potential loss of quality
  • Bacterial Growth Risk: This is the most significant risk associated with platelet storage. Room temperature allows bacteria potentially introduced during collection or processing to multiply
    • Implication: Strict aseptic collection, diversion pouches, and often bacterial detection testing (culture or rapid tests) are employed to minimize septic transfusion reactions. The limited shelf life also helps mitigate this risk

Plasma (FFP, PF24, etc.) - Stored Frozen (≤ -18°C)

Freezing dramatically slows down biochemical processes

  • Coagulation Factor Stability: The primary goal is to preserve the activity of coagulation factors
    • While Frozen: Factor levels are generally stable, especially at colder temperatures (≤ -30°C preferred for long-term storage of labile factors). However, even at -18°C, there is a very slow decline, particularly in the labile factors V and VIII. This decline dictates the typical 1-year expiration date
    • After Thawing: Once thawed and stored at 1-6°C, Factors V and VIII degrade much more rapidly. This is why thawed plasma must be transfused within 24 hours (or relabeled as “Thawed Plasma” with a 5-day expiry, acknowledging lower labile factor levels)
  • Other Components: Other plasma proteins (albumin, immunoglobulins, other coagulation factors) are generally very stable when frozen

Cryoprecipitated AHF - Stored Frozen (≤ -18°C)

As a concentrate derived from FFP, its properties relate to the specific factors it contains

  • Factor Stability: Contains concentrated Factor VIII, fibrinogen, Factor XIII, von Willebrand factor, and fibronectin
    • While Frozen: Stability is similar to FFP, with Factor VIII being the most sensitive labile factor. The 1-year expiration applies
    • After Thawing: Factor VIII activity declines rapidly, especially when stored at room temperature (20-24°C). Fibrinogen is more stable. The very short post-thaw expiration (6 hours unpooled, 4 hours pooled in an open system) reflects the need to maintain Factor VIII potency

Key Terms

  • Storage Lesion: The collection of biochemical and morphological changes occurring in Red Blood Cells during refrigerated storage
  • ATP (Adenosine Triphosphate): The main energy currency of cells
  • 2,3-DPG (2,3-Diphosphoglycerate): A molecule in RBCs that facilitates oxygen release from hemoglobin
  • Viability: The ability of transfused cells (especially RBCs) to survive in the recipient’s circulation. Often measured as % recovery at 24 hours post-transfusion
  • Hemolysis: The breakdown of red blood cells and release of hemoglobin
  • Labile Factors: Coagulation factors that degrade relatively easily during storage (esp. Factors V and VIII)
  • Swirling: The characteristic shimmering, swirling appearance of viable, discoid platelets when gently agitated, caused by light scattering. Loss of swirl indicates potential quality issues
  • Supernatant: The liquid portion bathing the cells in a blood component unit (plasma and/or additive solution)