Increased utilization, verification, and clinical implications of immunocytochemistry: Experience in a northern New England hospital

Background We report our experience in utilization, verification, and clinical implications of antibodies for use in diagnostic immunocytochemistry (ICC). Methods A computer search identified cytology cases utilizing ICC and corresponding surgical pathology material. Alcohol-fixed liquid based cytology (LBC) specimens were generated from surgical pathology bench specimens. ICC on LBC and immunohistochemistry on formalin fixed paraffin embedded tissue (FFPE) were performed in parallel for 71 commonly used antibodies. Cytology and corresponding surgical pathology reports were reviewed for all cases in which antibodies failed verification studies but had been used in the four years prior to implementation of our verification process. Results From 2007 to 2011, the number of cytology cases in which ICC was performed increased from 98 (or 5% of all non-Pap test/nonurine cytology cases in our laboratory) to 306 (or 15%). Verification studies revealed calretinin, CD5, c-kit/CD117, inhibin, napsin A, OCT 3/4, and PAX-5 to be nonreliable in LBC despite consistent immunoreactivity in concurrent IHC on surgical specimens. No antibodies were found to be immunoreactive on LBC but nonreactive on FFPE. No adverse clinical outcomes resulted from the use of nonverified antibodies. Conclusions Utilization of ICC at our institution has increased dramatically in recent years. Our verification process confirmed reliability in the majority of antibodies, but did identify several inconsistent antibodies. Although, in our series, no adverse clinical outcomes resulted from preverification use of these inconsistent antibodies, we encourage other institutions to confirm reliability of antibodies prior to use for diagnostic ICC. Diagn. Cytopathol. 2015. © 2015 Wiley Periodicals, Inc.