Aims This study aims to summarise published cases of reactive plasmacytosis to provide a resource to aid haematopathologists and clinicians in the diagnostic workup of reactive plasmacytosis.

Methods We searched published articles on reactive plasmacytosis on PubMed, Scopus and Google Scholar. Data were screened following Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. Cases were classified into six categories, namely: (1) infection, (2) angioimmunoblastic T-cell lymphoma (AITL), (3) other malignancies, (4) drug associated, (5) autoimmune diseases and (6) others. Plasma cell percentage in peripheral blood and/or bone marrow was tabulated. Descriptive statistics were reported as median with IQR, using JASP Team.

Results 87 articles which reported on 146 patients were included. Infectious diseases represented most cases associated with reactive plasmacytosis (n=46, 31% of all cases), with viral infections being the most frequent (n=31, 21% of all cases). AITL was the second most frequent aetiology (n=34, 23% of all cases), followed by medications (n=28, 19% of all cases), other malignancies (n=18, 12% of all cases), miscellaneous aetiologies (n=11, 7% of all cases) and autoimmune diseases (n=9, 6% of all cases). The absolute and relative levels of plasma cells in each diagnostic category showed marked variation and ranges largely overlapped between categories.

Conclusions In patients with an increase in the number and/or proportion of plasma cells in peripheral blood and/or bone marrow, clinical context and a broad differential diagnosis are necessary to direct further evaluation and arrive at a correct diagnosis. Our literature review suggests that evaluation for infectious causes and AITL may be of the greatest yield in many cases.