A novel technique to eliminate cross-contamination when making wells on slides for rabies diagnosis.

The direct fluorescent antibody (DFA) rabies diagnostic test requires demarcating desirable areas of brain tissue slip smear slides to be stained, traditionally achieved by applying paint from a tech pen or using a wax pencil to form a circle or dam-like ring or well into which rabies conjugate is expelled. Unfortunately, using these instruments poses a possibility of cross-contamination by transfer via the pen or pencil tip of rabies antigen from one slide to another. A new method was developed to avoid cross-contamination. The open end of a disposable glass test tube, dipped into a shallow reservoir of nail polish, was used to apply a dam-like ring about the slip smear area to be stained, after which the test tube was discarded, thereby precluding tissue transfer.