Novel fluorescent interference preventing peripheral CD34 + cell enumeration in a healthy, mobilized hematopoietic progenitor cell apheresis donor

Case Presentation A 34‐year‐old healthy related male allogeneic stem cell donor showed apparent mobilization failure. The recipient, the donor's mother, received a haploidentical conditioning regimen, but total body irradiation was delayed as a result. Stem cell collection was initiated while investigation for pre‐analytical and analytical laboratory error for CD34 cell enumeration was conducted. Clerical checks and repeat CD34 cell enumeration studies showed no discrepancies. Peripheral smears showed appropriate leukocytosis with prominent left shift. On review, flow cytometry plots demonstrated a shift from baseline in fluorescence intensity of background leukocytes in the CD34‐phycoerythrin channel obscuring a CD34+ cell population suggesting interference. A preanalytical saline wash resolved the interference. The final yield of the collected product was 16.2 × 10 6 CD34+ cells/kg recipient weight without evidence of interference. The recipient received irradiation, stem cells were infused, and successfully engrafted on Day 17, remaining in molecular remission 6 months post‐transplant. Discussion Potential interference mechanisms in flow cytometry assays include autofluorescence and non‐specific antibody binding. Possible interfering substances for consideration included cannabinoids, riboflavin, turmeric extract, and other compounds which may be present in marijuana edible gummies, which were disclosed by the donor during in‐depth history evaluation. Intraprocedural dilution, selective separation during apheresis, and pre‐analytical dilution likely eliminated the interference when testing the stem cell product. Conclusion Suspected mobilization failure may be due to interference/laboratory error. Sample dilution and washing may resolve interferences. In time‐sensitive cases, systematic investigation to rule out common causes of laboratory error is essential to avoid delays in patient care.