Optimizing the DNA yield for molecular analysis from cytologic preparations

Background: Cytology smears and cytospin preparations are increasingly being used for molecular testing. With these limited samples, optimizing tissue extraction to maximize the DNA yield is, therefore, critical. This study examined 2 common methods of tissue extraction and compared DNA yields from different types of glass slides.

Methods: The H226 lung cancer cell line and 5 clinical samples of cellular effusions were used to prepare Diff-Quik-stained cytospins on 4 types of glass slides: fully frosted (FF), nonfrosted (NF), positively charged (PC), and silane-coated (SC). Tissue extraction was performed by either scalpel-blade scraping or cell lifting with the Pinpoint Slide DNA Isolation System (Zymo Research). DNA was extracted with the QIAamp DNA Mini Kit (Qiagen) and was quantified with the Quant-iT PicoGreen Kit (Life Technologies).

Results: The DNA yield in cell-line cytospins was significantly lower from FF slides versus NF, PC, and SC slides with both scraping and cell-lifting methods. In addition, scraping yielded significantly more DNA than cell lifting (P = .005). DNA yields from 5 clinical effusion cases with FF and NF slides showed results similar to the results for cell-line samples, with scraping consistently yielding more DNA than cell lifting and with NF slides outperforming FF slides.

Conclusions: Optimizing the DNA yield extracted from cytology specimens maximizes the chances of successful molecular testing and is critical in cases of low or marginal cellularity. This study demonstrates the following: 1) scraping yields more DNA than cell lifting, and 2) NF slides yield more DNA than FF slides.