Effect of sample holding, cryopreservation, and storage on the human lymphocyte cytogenetic test

In monitoring occupational populations with the human lymphocyte cytogenetic test, it is not always possible to collect and process matched samples on the same day, even though this would be desirable to control for technical variables. The effects of holding samples for 24 hours at 4 degrees C and 22 degrees C, freezing lymphocytes in dimethylsulfoxide at -180 degrees C, and keeping fixed cells for 6 days at 4 degrees C before slide-making were examined. Final cell count, mitotic index, percentage of cells in first division, percentage of cells with chromosomal aberrations, and sister chromatid exchange per cell were measured in paired cultures. A significant increase in the frequency of cells with chromatid breaks occurred after prolonged fixation, so all other results were obtained from freshly fixed cells. Although holding at 22 degrees C and cryopreservation had significant effects on the mitotic index and entry of lymphocytes into the cell division cycle, the cytogenetic endpoints were not affected by any of the sample manipulations. Thus, samples can be held at 4 degrees C or 22 degrees C for 24 hours, or frozen lymphocytes can be stored for at least a week, without altering the cytogenetic endpoints.