The reliability of long-term storage of direct immunofluorescent staining slides at room temperature

Long-term preservation of immunofluorescence is important for re-examinations. We investigated whether the storage of direct immunofluorescent (DIF)-positive slides at room temperature was reliable in daily practice.

One hundred and twenty-five DIF-positive slides from the skin of 52 patients were evaluated. Sections were examined for the presence of immunoglobulin A (IgA), IgG, IgM, C3, and fibrinogen using fluorescein isothiocyanate-conjugated antisera and mounted with a ready-to-use permanent mounting medium containing an antifading reagent and sodium azide (DAKO, Glostrup, Denmark, S3023). The slides were stored at room temperature for 16-24 months. Changes in diagnostic pattern, fluorescence intensity, and the form and location of accumulation of immunoreactants and technical deformation were investigated.

Over the entire observation period, 49.6% of the slides faded away; the median length of survival was 16 months. Before 12 months, the survival rate of slides was 92.0%, whereas after 20 months it was 28.0%. In the early faded slides, which faded away before 16 months following the first examination, C3 and IgA were the most frequently observed immunoreactants. The technical deformations did not prevent the diagnosis.

The preservation of fluorescence in DIF-positive slides using mounting media with an antifading reagent is possible for 2 years at room temperature. However, in daily practice, storage for longer than 11 months prevents a reliable diagnosis.