3.4 Blood Component Quality Control

Component quality control asks a process question: if we sample production the way FDA and AABB require, do the components we label actually contain what the label claims? QC is not a second infectious-disease panel and it is not a test of every bag. It is a statistically and regulatorily defined sample plus a 100% visual inspection. Failures are manufacturing events.

AABB Standards 35th edition (effective 1 April 2026) is a subscription document; the numeric specifications taught below are the figures still published in 21 CFR Part 640, the Circular of Information, and current AABB/FDA summaries used with Technical Manual 21st-edition methods. Where a 35th-edition number is not publicly posted, this section uses the official published federal or AABB figure and does not invent a replacement.

The specification table

Memorize the table, then learn why each number exists. The exam will swap 5 × 10^6 with 5 × 10^8, 3.0 × 10^11 with 5.5 × 10^10, and 80 IU Factor VIII with 150 IU.

Leukoreduction

U.S. leukoreduction is defined by a residual white-cell count below 5 × 10^6 per unit. That cutoff is what makes a unit “leukocyte reduced” on an ISBT-128 product code. It is the specification tied to fewer febrile non-hemolytic reactions, reduced HLA alloimmunization, and CMV-safe inventory (leukoreduction is accepted as CMV-risk reduction; it is not a guarantee that every residual leukocyte is gone). Prestorage filtration is preferred because leukocytes degrade in the cold and release cytokines during storage.

Leukoreduction must not destroy the product. AABB therefore also requires ≥ 85% recovery of the original red-cell content. A filter that leaves 4 × 10^6 WBC but only 70% of the red cells has failed QC even though the WBC number looks good. Residual WBC QC is performed on a defined sample of production — not on every unit — using a method sensitive in the 10^6 range (typically a dedicated counting platform, not a routine automated CBC).

Platelet yield, pH, and swirl

21 CFR 640.24(c) is explicit: centrifugation must yield not less than 5.5 × 10^10 platelets per whole-blood-derived unit in at least 75 percent of units tested. AABB’s apheresis specification is a full adult dose: ≥ 3.0 × 10^11 in 90% of sampled units. Those are different products. A whole-blood platelet concentrate that contains 8 × 10^10 platelets is a passing whole-blood unit, not a failed apheresis unit.

pH must be not less than 6.2, measured at the storage temperature, at the end of dating (21 CFR 640.25). pH falls because platelets glycolyze and produce lactate. If residual plasma (or platelet additive solution) volume is too small, buffering collapses and pH crashes. That is why volume is a required monthly QC measurement alongside count and pH. A pH of 6.0 at outdate is a process failure even if the count was 4 × 10^11 on day 0.

Swirling — the shimmer of discoid platelets held to light — is a visual viability clue, not a numbered CFR limit. Loss of swirl, large aggregates, or a dark or bubbling bag are issue-time failures. They may indicate bacterial contamination or a storage-temperature/agitation break. Do not issue a non-swirling, discolored platelet because “QC last month was fine.”

Red-cell hematocrit, recovery, and viability

CPDA-1 packed cells keep only enough plasma for preservation. If too much plasma is stripped, hematocrit exceeds 80%, viscosity rises, and the remaining nutrient volume is inadequate. AABB’s ≤ 80% hematocrit limit is a CPDA-1 packed-cell rule. Additive-solution units are intentionally more dilute (about 55–65%) and are not judged against that 80% ceiling.

Recovery is the fraction of red cells remaining after a process (leukoreduction, washing, freezing/deglycerolization). Viability is the fraction of transfused cells still circulating at 24 hours. Frozen and rejuvenated red-cell processes are licensed on recovery-and-viability data (21 CFR 640.17), not on a hematocrit printout alone. If the exam asks what “acceptable frozen red cells” must demonstrate, the answer is in-vivo survival/viability plus safety and potency, not merely “it thawed.”

Cryoprecipitate — use 80 IU, not 150 IU, for Factor VIII

This is the number pair that unofficial outlines sometimes scramble. Confirm against the official texts:

• 21 CFR 640.56: test at least four representative containers each month. If the average antihemophilic factor (Factor VIII) potency is less than 80 units per container, take immediate corrective action.
• AABB Standards / Circular of Information: the manufacturing method must yield at least 150 mg fibrinogen and 80 IU Factor VIII per unit.

There is no official AABB 35th-edition or Technical Manual 21st-edition public figure that raises Factor VIII to 150 IU. Fibrinogen is 150 mg; Factor VIII is 80 IU. A question that offers “150 IU Factor VIII and 150 mg fibrinogen” is using a look-alike distractor. Cryo also contains Factor XIII, von Willebrand factor, and fibronectin, but those are not the FDA monthly potency specification.

Irradiation dose

To prevent transfusion-associated graft-versus-host disease, the irradiator must deliver 25 Gy (2500 cGy) to the center of the container and at least 15 Gy to any other part of the bag. That pair is the QC check (dose map, indicator label, and scheduled output verification). Underdosing the edge of a bag is a TA-GVHD risk. Overdosing is not the usual exam concern; the dating consequence of irradiation is potassium leak, already covered in 3.3. Cesium-137, cobalt-60, and X-ray irradiators are all acceptable if they meet the dose specification. A “irradiated” sticker without a validated dose is not QC.

Visual inspection — the 100% test

21 CFR 640.5(e) and 640.11 require visual inspection during storage and immediately before issue. Reject or quarantine for:

• Clots or masses in a red-cell or plasma bag.
• Hemolysis — purple or port-wine supernatant, or a red-cell unit whose plasma layer is frankly hemolyzed.
• Lipemia — marked milkiness that may be acceptable for some plasma uses but can hide hemolysis and may be unsuitable for certain patients or for further manufacture; follow SOP rather than assuming lipemia is always discard or always fine.
• Discoloration — brown, green-black, or bubbling suggesting contamination; some green plasma from oral contraceptives is a recognized benign finding, but unusual color is investigated, not ignored.
• Bag defects — leaks, broken ports, missing or detached segments, unreadable or conflicting ISBT-128 labels.

Platelets are inspected for swirl, aggregates, and color. Granulocytes and thawed products get the same “would I hang this?” look before issue.

Sampling frequency and what a failure means

FDA is specific where it is specific:

• Platelets (21 CFR 640.25): each month, test four units from different donors at the end of storage for count, pH (≥ 6.2 at storage temperature), and actual plasma volume.
• Cryoprecipitate (21 CFR 640.56): each month, test at least four representative containers for Factor VIII potency.

AABB expects a defined, statistically reasonable sample for leukoreduction, hematocrit, and other component attributes — commonly a monthly minimum in the same four-unit spirit, or a percentage of production set in the facility’s quality plan. The exact 35th-edition sample-size table is not a freely published federal number; do not invent “test 1% of every lot or 10 units, whichever is greater” as if it were CFR text unless your facility SOP uses that phrase.

If QC fails:

1. Quarantine remaining in-date products from the implicated process, instrument, or lot.
2. Do not release out-of-specification units on an exception signature.
3. Investigate — reagent, irradiator dose map, centrifuge protocol, filter lot, storage temperature, sampling error.
4. Correct and document before labeling resumes.
5. Look back at recently released units if the failure could have been present earlier (for example, an irradiator that has been under-dosing).

A single platelet with pH 6.1 at outdate is not “close enough.” It is a 21 CFR 640.25(b)(4) trigger for immediate corrective action.

Worked scenario. Monthly apheresis platelet QC: 4 units. Yields are 3.4, 3.2, 3.1, and 2.6 × 10^11. Three of four meet 3.0 × 10^11, which is 75%, not 90%. The process fails AABB’s 90% apheresis criterion even though the mean is above 3.0 × 10^11. Quarantine current inventory made by that procedure, investigate split-pack volume and instrument yield settings, and do not issue the 2.6 × 10^11 unit as a full apheresis dose. Separately, cryo monthly Factor VIII results of 90, 85, 78, and 88 IU average 85.25 IU — the FDA average is above 80, so the Factor VIII potency QC passes even though one container was below 80. Fibrinogen on those same units must still meet the AABB 150 mg expectation.

Exam traps. Residual WBC is < 5 × 10^6, not 5 × 10^8 (that older whole-blood leukocyte content is what you are reducing from). Apheresis yield is 3.0 × 10^11 / 90%; whole-blood yield is 5.5 × 10^10 / 75%. Cryo Factor VIII is 80 IU, fibrinogen is 150 mg. Irradiation is 25 Gy center / ≥ 15 Gy everywhere. QC failures quarantine and investigate; they do not get medical-director overrides into general inventory.