The certificate of analysis arrives with the shipment, gets glanced at, and goes into a folder. It is the densest piece of information you will receive about material you are about to build months of work on, and most of it is read as reassurance rather than as data. Read properly, a certificate tells you what the supplier is prepared to stand behind, which is a different and more useful thing than what the material is.
Viability, and the question of when
Viability is the number everyone looks at and the number most often misread. It records the fraction of cells excluding a dye at one moment, by one method, in one operator’s hands. The critical missing variable is usually when.
Pre-freeze viability and post-thaw viability are different measurements of different things, and a certificate that does not say which one it is reporting has told you very little. Pre-freeze tells you the isolation went well. Post-thaw tells you what you will actually be working with. A high pre-freeze figure on material you intend to thaw is close to decorative.
The second missing variable is method. Trypan blue exclusion, acridine orange with propidium iodide, and flow-based viability dyes do not return identical numbers on the same sample. Comparing a figure from one supplier against a figure from another, generated by a different method, is a comparison of methods as much as of material.
Purity, and by which measurement
Purity means the proportion of the preparation that is the cell type you ordered, and it is only interpretable alongside the gating or selection strategy behind it. A CD56+ purity figure assumes a particular gate on a particular panel. Change the gate and the number moves without anything about the cells changing at all.
What to look for is whether the certificate names the marker and the method. OrganaBio lists CD56+ purity at 90% or above on the cord blood NK cells, alongside the isolation approach, which is what makes the figure checkable rather than merely reassuring.
Recovery, which is the one people skip
Recovery is the proportion of cells you get back relative to what went in, and it is the quiet predictor of whether your experiment will have enough material. Viability can be excellent while recovery is poor: the cells that survived are healthy, there are simply fewer of them than you planned around. If a certificate reports viability without recovery, your yield calculation is running on an assumption.
Cell count and how it was determined
A count is a count multiplied by a volume, and both halves carry error. Automated counters and manual haemocytometer counts disagree, particularly on preparations with debris, and debris is exactly what a post-thaw preparation contains. Where a supplier states a documented minimum rather than a lot-specific figure, as OrganaBio does with the minimum of 10 billion cells per single-donor leukopak unit, that is a floor you can plan against rather than a measurement of your particular unit.
Safety testing
Sterility, endotoxin and mycoplasma are the three that appear most often, and they answer narrow questions. Sterility asks whether the preparation grew anything under defined culture conditions. Endotoxin quantifies bacterial cell wall material, which matters because it activates immune cells and can distort exactly the assays you bought the material for. Mycoplasma is the contaminant that does not announce itself, changing cell behavior without changing appearance.
A certificate that reports these as tested and passed is more useful than one that reports them as not detected without stating the limit of detection, because a detection limit is what makes the result interpretable.
The donor block
This is where certificates diverge most between suppliers, and where the difference in value is largest. A donor identifier alone lets you correlate lots. Screening status tells you the material is safe to handle. Characterization, meaning HLA genotype, KIR genotype and donor attributes, tells you how the material is likely to behave and lets you explain variance later instead of guessing at it.
OrganaBio’s donor program documents a 14-marker infectious disease screening panel, high-resolution NGS HLA genotyping across HLA-A, HLA-B, HLA-C, HLA-DR, HLA-DQ and HLA-DP, and KIR genotyping. The reason that combination matters is covered in more depth in the HLA typing guide.
Related product
Leukopak formats. Single-donor starting material, fresh or cryopreserved, with full donor documentation.
Line by line
| Line | What it tells you | What it does not |
|---|---|---|
| Viability | Fraction excluding dye at the stated timepoint | How the cells will function, or how they behave after a rest period |
| Purity | Proportion matching the named marker under the stated gate | Anything, if the marker and method are unstated |
| Recovery | Whether you will have enough material | Whether what you recovered is representative |
| Cell count | Planning figure, subject to counting method | Live cell count, unless paired with viability at the same timepoint |
| Sterility | Nothing grew under defined conditions | Absence of organisms outside those conditions |
| Endotoxin | Level of a known assay-distorting contaminant | Much, without a stated limit of detection |
| Donor identifier | Lets you correlate lots from the same person | Whether you can obtain that donor again |
| HLA and KIR | How the material is likely to behave immunologically | Function, which still has to be measured |
The missing line
Sometimes a field is blank, and the instinct is to read it as an oversight or as an implied guarantee. Neither is safe. A blank field means no threshold is published.
There are legitimate reasons for that. A whole leukopak is heterogeneous starting material, and a single viability figure across the entire unit would be close to meaningless, so some suppliers decline to publish one rather than produce a number that cannot carry weight. OrganaBio takes that position explicitly on whole leukopak formats and states it on the product record instead of leaving the gap open to interpretation, while publishing thresholds where the material supports them, as with post-thaw viability listed at 85% or above on the peripheral blood NK cells.
What to do with it
Read the certificate before the material is committed to an experiment, not after a result surprises you. Confirm which timepoint each figure refers to, confirm the method behind purity and viability, check that recovery is present, and treat the donor block as experimental metadata rather than as paperwork. When a functional result later refuses to reconcile, that block is where the explanation usually is.
Frequently asked questions
What should a certificate of analysis for primary cells include?
Viability with a stated timepoint and method, purity with the named marker and gating approach, recovery, cell count with the counting method, safety testing such as sterility, endotoxin and mycoplasma with limits of detection, and a donor block covering identifier, screening status and characterization.
What is the difference between pre-freeze and post-thaw viability?
Pre-freeze viability records how well the isolation went. Post-thaw viability records what you will actually work with. For material you intend to thaw, the post-thaw figure is the relevant one, and a certificate that does not state which timepoint it reports has told you very little.
Why do viability numbers differ between suppliers?
Different methods return different numbers on the same sample. Trypan blue exclusion, acridine orange with propidium iodide and flow-based viability dyes do not agree, so comparing figures across suppliers without knowing the method compares methods as much as material.
Why does recovery matter as much as viability?
Recovery is the proportion of cells returned relative to input, and it determines whether you have enough material. Viability can be high while recovery is poor, meaning the surviving cells are healthy but fewer than you planned around.
What does a blank field on a certificate mean?
It means no threshold is published, not that a guarantee is implied. There are legitimate reasons, such as a heterogeneous whole-unit format where a single figure would be misleading. What is informative is whether a supplier is consistent about where numbers appear.
Why is endotoxin testing relevant for immune cell work?
Endotoxin is bacterial cell wall material that activates immune cells. Present at meaningful levels, it distorts precisely the functional assays that immune cell preparations are usually purchased for. A result is only interpretable alongside a stated limit of detection.
Is the donor information on a certificate just paperwork?
No, it is experimental metadata. Donor identifier lets you correlate lots, screening status establishes safe handling, and characterization such as HLA and KIR genotype predicts immunological behavior. When a functional result later fails to reconcile, the donor block is usually where the explanation sits.
Talk to OrganaBio
Working through this on a live program?
The scientific team works through sourcing and specification questions with cell therapy and research groups directly, including donor characterization, format selection and documentation scope.
