PREreview of Hemoglobin Dose and Red Cell Transfusion: Component Variability, Oxygen Function, and Measurement Uncertainty

This narrative review highlights four core findings regarding red blood cell (RBC) transfusion: first, prescribing by unit count leaves the actual administered hemoglobin mass unspecified, while recipient hemoglobin increments are confounded by blood volume, fluid balance, ongoing bleeding, and cell survival; second, blood components meeting identical quality specifications still vary substantially in hemoglobin mass and are further altered by anticoagulants, additive solutions, container materials, and processing; third, hemolysis shifts hemoglobin between cellular and extracellular compartments while posttransfusion recovery determines cell persistence; and fourth, concentration and mass measurements alone fail to capture functional oxygen delivery, which depends on oxygen affinity and oxygen-release kinetics. Building on these findings, the work moves the field forward by shifting transfusion practice from an assumption of unit equivalence toward explicit, individualized component characterization within existing compatibility and patient blood management frameworks, and by establishing a stepwise blueprint for prospective clinical studies that link standardized final-component measurements to delivered volume, recipient physiology, and timed sampling to test first whether measured hemoglobin mass improves increment predictions and second whether oxygen-release and perfusion variables improve physiological and clinical patient outcomes.

Major issues

• Selection bias inherent to narrative reviews: Because this work is a narrative rather than a systematic review, it lacks standardized literature search protocols, explicit inclusion/exclusion criteria, and formal risk-of-bias assessments, leaving room for selective citation of evidence favoring content-based allocation.

• ​"Representative" versus direct unit-level measurement: Proposing to link "representative final-component measurements" to recipient outcomes introduces a methodological tension—relying on batch or surrogate averages fails to resolve the unit-to-unit variability the authors highlight, whereas invasively sampling every individual bag risks bacterial contamination, volume loss, and altered storage integrity.

• ​Operational and technical barriers to functional assays: Quantifying oxygen affinity (P50) and oxygen-release kinetics requires specialized instrumentation, strict quality standardization, and turnaround time that are difficult to integrate into routine blood-bank workflows, particularly during acute hemorrhage or in resource-limited clinical settings.

• ​Dominance of dynamic recipient confounders: Even with exact measurements of administered hemoglobin mass, unstable clinical variables—including rapid crystalloid or colloid resuscitation, third-spacing, occult ongoing bleeding, and variable splenic sequestration—can easily outweigh input-dose precision when predicting post-transfusion hemoglobin increments.

• ​Inventory fragmentation and blood wastage risks: Stratifying RBC inventory by granular component metrics (hemoglobin content and oxygen-unloading kinetics) alongside standard ABO/Rh crossmatching complicates stock management, potentially delaying urgent allocations and increasing expiration rates for lower-mass or longer-stored units.

• ​Undefined clinical thresholds and endpoint specificity: While the framework notes that clinical benefit requires independent physiological and patient outcomes, it does not specify what constitutes a clinically meaningful gain in increment prediction, which standardized perfusion metrics should be prioritized, or how trials will be powered to link component characterization to reduced morbidity or mortality.

Minor issues

• Reference citation inside the abstract: Including a numbered citation ([1]) in the abstract disrupts reading flow and conflicts with standard journal formatting conventions, which typically reserve references for the main text.

• ​Terminology precision and parallel phrasing: Replacing "recipient increment" with "recipient hemoglobin increment" would mirror the earlier phrase "concentration increment" and prevent ambiguity. Additionally, defining the abbreviation hemoglobin (Hb) at first mention would streamline repetitive phrasing across dense sentences.

• ​Ambiguity in "samples collected at defined times" and "delivered volume": Specifying "timed post-transfusion recipient blood samples" clarifies who is being sampled and when, while clarifying whether "delivered volume" refers to total infused component volume or net red cell volume would sharpen the methodological description.

• ​Abrupt transition between review synthesis and study proposal: The text moves directly from summarizing mechanistic factors (hemolysis, recovery, oxygen-release kinetics) to proposing prospective trials ("We propose prospective studies..."). Adding a brief transitional clause—or organizing the abstract with structured subheadings (e.g., Context, Synthesis, Future Directions)—would improve narrative flow.

• ​Consistent punctuation and copyediting: Adding serial (Oxford) commas to multi-item lists (such as "fluid balance, bleeding, and cell persistence" and "preparation, storage, and clinical studies") would make complex sentences easier to parse, alongside minor copyediting fixes like standardizing hyphenation ("post-transfusion") and adding the missing period at the end of the final sentence.

Competing interests

The author declares that they have no competing interests.

Use of Artificial Intelligence (AI)

The author declares that they did not use generative AI to come up with new ideas for their review.