3.1 Processing, Testing & Labeling

Processing, Testing & Labeling

Quick Answer: Before any donated unit can be released for transfusion, it must be centrifuged into components, typed for ABO/Rh, screened for unexpected antibodies, and tested against a full infectious disease marker panel. Every result must resolve favorably (or be appropriately worked up) before the unit is labeled with an ISBT-128 barcode and released. This section covers the required testing panel, how repeat-reactive results are handled, and the FDA/AABB labeling elements a compliant unit must carry.

From Whole Blood to Components

Within hours of collection, whole blood is separated by differential centrifugation into its components — red blood cells, platelets, and plasma — because each component has different storage requirements and clinical uses. A "hard spin" separates plasma from the cellular layer; platelet-rich plasma can then be given a second "light spin" to separate platelet concentrate from platelet-poor plasma. Processing must occur within specified time windows relative to collection (commonly within 6–8 hours for platelet production from whole blood, and within 8 hours if plasma is to be used for coagulation factor products) because holding temperature and elapsed time directly affect factor VIII activity and platelet viability. Facilities validate their own hold times and centrifugation protocols against AABB Standards and FDA guidance rather than relying on a single universal number, since equipment and protocols vary.

I.B — Mandatory Testing Panel

Every donation, no matter how many times the donor has given before, undergoes the same core testing panel prior to release:

ABO and Rh Typing

Forward (direct) typing determines the antigens present on the donor's red cells using anti-A and anti-B reagents; on first-time donors, AABB Standards require confirmatory testing on a separate sample to verify ABO group before labeling, as a safeguard against sample mix-up. Rh(D) typing uses anti-D reagent; donors whose cells are weakly or discrepantly reactive must be resolved before the unit can be labeled Rh-positive or Rh-negative — many facilities label discrepant results as Rh-positive out of caution (a falsely-labeled Rh-negative unit given to an Rh-positive recipient is far more consequential than the reverse) or perform weak D testing to resolve the discrepancy.

Antibody Screen

Donor plasma or serum is screened against reagent red cells to detect clinically significant unexpected antibodies (e.g., anti-K, anti-Jka). A positive screen requires antibody identification; if a clinically significant antibody is identified, plasma and platelet products from that donation are typically restricted or the donor is flagged so recipient crossmatching accounts for it. RBC units themselves are not affected by donor antibodies since the plasma is removed, but a donor's own antibody history matters for donors who plan to give again.

Infectious Disease Testing Panel

FDA-mandated infectious disease testing on every donation (conceptually, not exhaustively) includes:

Nucleic acid testing (NAT) shortens the infectious window period compared to antibody/antigen testing alone by detecting viral genetic material directly, which is why HIV, HBV, and HCV each pair a serologic test with a NAT assay. Exact required markers and testing technologies are FDA-guidance-dependent and updated periodically — candidates should know the categories and rationale (antibody vs. antigen vs. NAT, window-period reduction) rather than memorizing a single frozen list, since guidance documents are revised as epidemiology and assay technology change.

Repeat-Reactive Results, Confirmatory Testing, and Donor Deferral

A donation with a reactive infectious disease screening result is not automatically "positive" — it is repeat-reactive if the initial reactive result is confirmed on retesting (per the assay's package insert protocol, often testing the same sample in duplicate). A confirmed repeat-reactive result triggers:

1. Unit quarantine and discard — the unit and all associated components are not released
2. Donor notification — the facility must notify the donor per FDA requirements
3. Donor deferral — indefinite or permanent deferral depending on the marker and confirmatory result
4. Look-back investigation — for markers with recognized window periods, prior donations from the same donor may need to be traced, and previously transfused recipients or unused components identified, since the donor may have been in an infectious window period during an earlier, seemingly-negative donation
5. Supplemental/confirmatory testing — additional, more specific assays (e.g., for HBV, testing for anti-HBs and additional markers) to distinguish true infection, resolved past infection, or biological false-positivity, which matters for whether a donor may ever be re-entered

Donor re-entry after a repeat-reactive screening result (in the absence of confirmed infection) is possible under FDA-defined re-entry protocols requiring a waiting period and additional negative testing, but a confirmed positive result (e.g., confirmed HIV or HCV infection) results in permanent deferral.

I.B — ISBT-128 Labeling

ISBT-128 (International Society of Blood Transfusion 128) is the globally standardized labeling system that replaced the older Codabar system in the U.S. It uses linear and 2D barcodes to encode, in machine-readable form:

• Donation identification number (DIN) — a unique 13-character identifier tying the unit to donor, collection facility, and collection date
• Product code — a 5-character code (from a standardized product description code database) identifying exactly what the component is (e.g., irradiated, leukocyte-reduced, specific anticoagulant)
• ABO/Rh group
• Expiration date (and, where applicable, expiration time)
• Special attributes (e.g., CMV-negative, irradiated) via additional facility-applied labels

ISBT-128's key advantage over Codabar is a single, unambiguous global numbering scheme that prevents donation-number collisions across facilities and countries, and its barcode structure supports scan-based verification at multiple checkpoints (collection, processing, labeling, issue, bedside administration) to reduce transcription and mislabeling errors — historically one of the most dangerous categories of transfusion error because a mislabeled ABO group can cause a fatal hemolytic transfusion reaction.

FDA/AABB Required Label Elements

A compliant final container label (per 21 CFR 606.121 and AABB Standards) must display, at minimum:

Any unit missing a required label element, or with an internal label discrepancy (e.g., ABO on the bag doesn't match the testing record), must be investigated and cannot be released until resolved — this is a common quality control hold point audited during inspections.

Practical Test-Taking Focus

SBB exam items on this topic tend to test conceptual understanding of why a testing or labeling step exists (window period reduction, mislabel prevention, donor safety) rather than requiring memorization of every current FDA-required marker, since guidance is periodically updated. Know the categories (serology vs. NAT), the purpose of confirmatory/supplemental testing, and the function of ISBT-128 versus Codabar.