Purpose: To assess the extent and the sources of variation in ISCN nomenclature used by participants in CAP/ACMG surveys dealing with fluorescence in situ hybridization (FISH).
Methods: Over 1600 nomenclature strings from 15 challenges in seven surveys were evaluated for the contributions of diagnostic errors, syntax errors, methodological differences, and technical factors not foreseen by ISCN 1995.
Results: Although diagnostic errors were uncommon, syntax errors were numerous, approaching 50% of the responses for several challenges. Their frequency varied with the complexity of the nomenclature required to describe a test condition. Variation attributable to probe selection and band designation correlated with the number of probes available for addressing the diagnostic issue at hand. In the most dramatic example of this effect, a survey simulating diagnosis of trisomy 21 in uncultured amniocytes, there were 66 participants (of 99) who used the same general form for their nomenclature, but only 8 of the 66 had exactly the same nomenclature string. Participants used proprietary names, created their own nomenclature, or ignored the true complexity of probe systems when trying to describe conditions not foreseen by ISCN 1995.
Conclusion: The use of current ISCN FISH nomenclature resulted in survey participants describing unique biological conditions in a multitude of different ways. In addition to making the nomenclature unsuitable for proficiency test purposes, this heterogeneity makes it impractical for clinical test reporting and for cytogenetic database management. Because methodological information contributes a large amount of variability, adds complexity, and increases opportunities for syntax errors, a system that excludes such information would be more effective.