American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

What action should be taken if high non-specific background is observed on a FISH slide post-wash?

1. Decrease postwash temperature

2. Increase postwash temperature

3. Shorten the wash time

4. Change the hybridization buffer

The correct answer is: Increase postwash temperature

Increasing the postwash temperature is a crucial step when addressing high non-specific background on a FISH (Fluorescence In Situ Hybridization) slide. When the postwash temperature is elevated, it can enhance the stringency of the wash conditions. This increased stringency helps in removing non-specifically bound probes or oligonucleotides that may remain attached to the slides due to incomplete washing or suboptimal hybridization conditions. The key to successful FISH procedures lies in the balance between probe specificity and background fluorescence. By raising the temperature during the wash phase, you promote a more selective removal of non-specific binding, allowing for clearer signals from specifically hybridized target sequences. This is particularly important in cytogenetics, where clarity and accuracy in imaging are paramount for valid interpretations of genetic material. The remaining options, such as adjusting wash time or changing the hybridization buffer, may improve results under certain circumstances, but they do not specifically target the issue of high non-specific background as effectively as increasing the postwash temperature does.