In the assay, a known number of cells from a sample are plated at low density in culture. Only cells capable of both surviving and dividing repeatedly will form a colony large enough to count, so the result reflects proliferative capacity, not simply the presence of cells.
The assay is considered more stringent than a simple viability or marker count, because dead or senescent cells, and cells that are alive but no longer capable of division, will not form colonies. A 2021 study of five commercial umbilical cord allograft products reported no colony-forming mesenchymal stromal cells in any of the products tested.
A CFU result, or its absence, is one of the more direct ways to evaluate whether a tissue product contains functionally proliferative cells, as distinct from cellular material generally. Ask a supplier whether CFU data exists for a specific product family and, if so, on what sample it was generated.
A colony-forming result, or its absence, is one of the clearest available data points for evaluating a cell-related claim, more direct than marker expression alone.