4.1 Whole Blood & Red Blood Cells

Whole Blood: A Legacy Component With Narrow Modern Indications

Whole Blood (WB) is a single unit of blood collected directly from a donor into a bag containing an anticoagulant-preservative solution, with no component separation performed. A standard collection is 450 mL or 500 mL of blood (±10%) drawn into a proportional volume of anticoagulant. Because nearly all whole blood collected in the U.S. is separated into components (Red Blood Cells, plasma, and platelets/cryoprecipitate) within hours of collection to maximize the clinical yield of a single donation, transfusable Whole Blood is now a minor, specialized product rather than a routine inventory item.

Modern indications for Whole Blood are narrow and specific: (1) exchange transfusion in neonates, (2) massive hemorrhage and exsanguinating trauma in settings (military, rural, or civilian trauma centers using low-titer group O whole blood, or LTOWB) where rapid balanced resuscitation is logistically difficult with separated components, and (3) cardiopulmonary bypass priming in some pediatric cardiac surgery programs. LTOWB programs screen group O donors for low anti-A/anti-B titers (commonly below 256) to allow use in non-group-O recipients without a formal crossmatch delay, reflecting a resurgence of interest in Whole Blood for trauma resuscitation.

Anticoagulant-Preservative Solutions and Storage Duration

The anticoagulant-preservative solution chosen at collection determines both red cell storage duration and metabolic quality. The SBB must know each formulation and its consequences cold.

Units collected in CPD, CP2D, or CPDA-1 without an additive solution retain a hematocrit of roughly 70-80%, because all of the original plasma volume beyond what is needed for anticoagulation has been removed with minimal replacement fluid. Once an additive solution (about 100 mL) is added to the packed cells after plasma and/or platelet-rich plasma removal, the hematocrit drops to approximately 55-65%, producing a less viscous, more easily transfused unit — a major reason additive solutions became the U.S. standard.

Preparing Red Blood Cells

Red Blood Cells (RBCs) are the component remaining after centrifugation removes most of the plasma (and, if the facility separates platelets, the platelet-rich or platelet-poor plasma layer) from a Whole Blood collection. A single unit contains approximately 200 mL of red cells, with a final volume of 300-400 mL once resuspended in additive solution, and it must be stored continuously at 1-6°C. RBCs are the mainstay product for correcting symptomatic anemia and are far more commonly transfused than Whole Blood.

Dosing rule of thumb: one unit of RBCs in a 70 kg adult raises hemoglobin (Hb) by approximately 1 g/dL (or hematocrit by roughly 3%), assuming no ongoing loss. A patient with active bleeding or hemolysis will show a smaller-than-expected increment, which the SBB should recognize as a clinical clue rather than a laboratory error.

The Storage Lesion

During refrigerated liquid storage, RBCs undergo a well-characterized set of biochemical changes collectively called the storage lesion. The SBB exam tests both the mechanism and the clinical consequence of each change.

Falling 2,3-diphosphoglycerate (2,3-DPG): 2,3-DPG stabilizes deoxyhemoglobin and shifts the oxyhemoglobin dissociation curve to the right, favoring oxygen release to tissue. As 2,3-DPG falls during storage (to under 10% of normal by roughly two weeks in non-rejuvenated units), the curve shifts left, and transfused cells temporarily bind oxygen more tightly and release it less readily. 2,3-DPG regenerates in vivo within 24-72 hours post-transfusion, so the clinical effect is transient but relevant in massive or rapid transfusion of critically ill patients.

Falling adenosine triphosphate (ATP): ATP is required for red cell membrane deformability and shape maintenance. As ATP depletes, cells transition from smooth discocytes to crenated echinocytes, and post-transfusion in vivo recovery declines — this is the biochemical basis for the FDA/AABB minimum 75% 24-hour post-transfusion recovery requirement used to validate maximum storage durations.

Rising extracellular potassium: As the sodium-potassium ATPase pump slows (less ATP available) and cell membranes leak, intracellular potassium exits into the supernatant plasma or additive solution, accumulating over storage. This matters clinically for rapid, large-volume transfusion into neonates or renally compromised patients, and it is the reason irradiated units — which leak potassium faster — carry a shortened outdate, covered later in this chapter.

Rising free plasma hemoglobin and microparticles: Ongoing low-level hemolysis releases free hemoglobin and generates red cell-derived microparticles, both of which increase with storage age and are markers of storage lesion severity.

Falling pH: Continued glycolysis produces lactic acid, and pH falls progressively, further slowing glycolysis in a self-limiting cycle — this is why phosphate-buffered CPD outperformed ACD, and why adenine in CPDA-1 extends usable storage by keeping ATP synthesis running longer.

Applying This to Practice

An SBB candidate should recognize that day-30 versus day-5 RBC units differ biochemically, but current evidence has not shown a clinically meaningful outcome difference between fresher and older units within the approved storage window for most patient populations — a key point after several large randomized trials (ABLE, RECESS, INFORM) failed to show benefit from fresher blood. The SBB should not confuse the existence of a storage lesion with an assumption that fresher blood improves outcomes; the exam frequently tests this distinction.