DLC-ICE: Absolute Counts Need a Volume Trail, Not Only a Correlation

The denominator has a physical history

An absolute cell concentration refers to the original specimen, not merely to the suspension that reaches the cytometer. Every volume transfer, loss and reference material used in the calculation therefore belongs to the measurement record. A stable percentage among recovered cells can coexist with an incorrect concentration in the original blood. Laboratories should decide which output they need before evaluating a stored-sample workflow.

What was qualified

Imbratta and colleagues qualified DLC-ICE using healthy-donor material across five processing sites. The 27-colour fresh-versus-fixed comparison used ten donors. Staining variability and anticoagulant robustness were assessed at one site. The main text reports negative count bias and greater uncertainty for rare subsets, and notes reduced CCR7/CD27 resolution. Immediate fixation prevents functional assays requiring viable cells. This is a 2023 original study in Cytometry Part A, not a new 2026 clinical guideline.

The points below are CFCM's proposed transfer and reporting framework; they are not additional results from the study.

Audit the arithmetic before judging the scatterplot

A bead-ratio count relates cellular events to reference-bead events and scales that ratio by the number of reference beads added and the original blood volume represented. Preserve units at every step. Microlitres of original blood, final resuspension volume and acquired volume are not interchangeable labels. If an aliquot is split, the record must show how the original-volume equivalent was carried forward.

For an explicitly hypothetical example, a cellular-to-bead event ratio of 0.5, twenty thousand reference beads and an original-volume equivalent of one hundred microlitres yield one hundred cells per microlitre. This calculation assumes that the reference and sample inputs are known and appropriate; it does not demonstrate recovery or accuracy. The example is educational arithmetic, not a study result or patient record.

Separate processing proficiency from staining proficiency

CFCM would keep separate records for the person who prepares the source aliquot, the person who thaws and stains it, and the person who acquires and analyses it. This makes corrective training more specific. A combined performance number can conceal where variability entered and can encourage an unnecessary change to a step that was already consistent.

Define local acceptance criteria before assessment, including how many evaluable comparisons are needed and how exceptions will be handled. Failed specimens should remain in the report with their reason. Repeating only failures until they pass can make a proficiency programme look better without improving the reliability of routine work.

Correlation is a starting point for agreement

Two methods can track each other closely while one consistently reports a lower result. Examine paired differences, proportional effects and the range relevant to the intended decision. Avoid allowing an abundant population to dominate a pooled regression when a less abundant population is the clinical target. Each claimed result deserves an acceptance rule that matches its consequences.

For a proposed rare-subset application, plan event adequacy, replicate precision and a route for results that cannot be quantified reliably. Distinguish an observed population from an accurate concentration, and distinguish both from a validated decision threshold. A research-panel transfer should not silently acquire the status of an interchangeable diagnostic test.

Preserve the distinction between phenotype and function

Before accepting a preserved specimen, describe the question in operational terms. Measuring a marker present at collection and measuring a subsequent response to stimulation are different experiments. Confirm that the planned specimen can support the required operation, and record any limitations in the interpretation rather than treating all immune profiling as a single capability.

Daily Learning Pill

A percentage answers a compositional question. A concentration also depends on a physical volume trail. Good agreement for one cannot substitute for evidence about the other.

Next step

Build a volume-and-operator worksheet before adopting stored whole-blood enumeration. Explore the CFCM resources. This original ChatGPT/Codex educational appraisal is not independent peer review, reanalysis of source FCS data or local clinical validation.