Interlaboratory variation in DNA flow cytometry. Results of the College of American Pathologists' Survey.

The results of the DNA Analysis Module of the College of American Pathologists' Flow Cytometry Survey were analyzed to determine if participating laboratories could correctly identify aneuploid populations and estimate S-phase fraction reproducibly in proficiency specimens. Each survey contained three specimens: a diploid calibrator and two unknowns comprising cultured aneuploid tumor cells with DNA indexes of 1.2 to 2.0 admixed with normal lymphocytes. Results of ploidy analysis were obtained from a mean of 241 participants on 19 unknowns from 1990 to 1992. Most laboratories correctly reported the modal (and intended) number of aneuploid peaks; the proportion of correct responses ranged from 58% to 97%, with a mean of 86%. The lower percents of correct response were associated with near-diploid and tetraploid unknowns. Some laboratories showed consistent deviations from the mean for DNA index, indicating apparent instrument linearity problems. S-phase results on five specimens showed wide interlaboratory variability, although the means of participants' responses were close to the reference values obtained by the specimen provider.