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Background aims An accurate and reliable assessment of bone marrow engraftment (BME) after hematopoietic stem cell transplantation (HSCT) is based on the ability to distinguish between recipient and donor cells at selected polymorphic short tandem repeat (STR) DNA loci. Buccal cells are an important source of DNA for determining the recipient's constitutional genotype, particularly in patients transplanted before the STR evaluation. Methods Genomic DNA was extracted from the recipient buccal cells and from isolated CD3+ (T-cell lymphocyte) and CD33+ (myelocyte) cells after HSCT. BME analysis was performed using a STR-based polymerase chain reaction amplification method followed by fragment-size analysis for assessing the recipient-derived or donor-derived composition of cell lineage-specific peripheral blood DNA. Results We identified three cases of complete buccal epithelial cell engraftment after HSCT detected by BME analysis, potentially leading to misinterpretation of testing results if these cells were used as the sole source for determining the recipient's genotype. Conclusions These cases suggest that complete engraftment of buccal epithelial cells may be a common finding in patients receiving HSCT, drawing attention to important issues such as the type of samples used for determining a patient's constitutional genotype that may confound testing results. This study also highlights the need for careful interpretation of the BME testing results in the context of the clinical findings.

dency or variability to aid in the interpretation of results. For 10/19 units viability method was not specified but obtained upon inquiry. The correlations between CD34 7-AAD, trypan blue (r 1⁄4 0.48, r 1⁄4 0.44) CFCs (r 1⁄4 0.41) or CBB viability to recipient engraftment (r 1⁄4 0.06) were not significant. Conclusion: Post-thaw viabilities and CFCs showed significant variation between reporting cord blood banks and our internal assessment, and had no correlation with engraftment. This study highlights limitations of inter-facility product comparisons, and suggests it is necessary to establish consistency in characterization of cord blood units.