The effect of the small amount of formaldehyde in the SurePath liquid when establishing protocols for immunocytochemistry

BACKGROUND: SurePath(®) is an ethanol-based liquid fixative. In addition to ethanol, it also contains a small amount of formaldehyde (<0.2%). The aim of this study was to investigate the immunoreactivity of cells stored for different lengths of time in the SurePath liquid. MATERIALS AND METHODS: Rest material from one malignant and three benign effusions were fixed in SurePath for 1–12 days. Cytospins were incubated with cytokeratin 7 antibody (AB) to evaluate the staining intensity of carcinoma cells and benign, reactive mesothelial cells. Protocols varied as to pretreatment and AB incubation time. RESULTS: Reduced immunostaining intensity was seen within 5 days of storage in the SurePath liquid. It was restored when the pretreatment time was prolonged. CONCLUSIONS: The small amount of formaldehyde in the SurePath liquid seems to affect the immunoreactivity. Local immunocytochemistry protocols in the cytology laboratories should consider this when optimizing their procedures. Postfixation with formalin should be omitted.