CD138 (Syndecan-1) Immunohistochemistry

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 30, 2026

CD138 (Syndecan-1) immunohistochemistry is a specialized staining technique applied to endometrial biopsy specimens to identify plasma cells, whose presence in the endometrium, where they are normally absent, is the key diagnostic finding in chronic endometritis.¹ CD138 (syndecan-1) is a transmembrane proteoglycan expressed on plasma cells and certain epithelial cells; because plasma cells are normally absent from the endometrium, CD138 staining identifies them and serves as the marker of chronic endometritis. Standard histologic staining (H&E) misses plasma cells at clinically significant rates; CD138 immunostaining substantially improves detection sensitivity, making it the current diagnostic standard when chronic endometritis is suspected.¹ Diagnostic thresholds vary by laboratory, but most published protocols flag one or more CD138-positive plasma cells per high-power field as abnormal. In the RRM workup, CD138 testing is considered particularly in couples with recurrent pregnancy loss or repeated implantation failure, where an undetected chronic endometritis may be a treatable contributing cause.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.