Comparison of plasma cell bone marrow counts by different methods in patients diagnosed with plasma cell disorders.

Introduction: Plasma cell quantification in bone marrow is important for diagnosis, prognosis, and treatment of plasma cell diseases. It can be performed by several methods such as aspiration, imprint and flow cytometry, and biopsy.

Objectives: To compare plasma cell counts at diagnosis of plasma cell diseases using different methods.

Methods: An observational study was carried out of laboratory results of adult patients with plasma cell diseases, who underwent aspiration, imprint cytology, flow cytometry (CD38, C138) and biopsy in a single institution between January 2015 and May 2021. The intraclass correlation coefficient was used to assess agreement between different methods with results stratified into three groups: <10%; 10-59% and ≥60% of infiltration.

Results: Sixty-seven cases were studied: 59.7% were men with a median age of 70 (range: 32-85) years. The diagnoses were multiple myeloma in 61%, gammopathy of undetermined significance in 25.4%, smoldering myeloma in 6% and other plasma cell dyscrasias in 7.6%. Less than 10% infiltration was found in 32 (47.7%), 35 (52.2%), 44 (65.7%) and 25 (37.3%) of patients, respectively by aspiration, imprint cytology, flow cytometry and biopsy. Infiltration ≥60% was detected in 7 (10.4%), 4 (6.0%), 2 (3.0%) and 21 (31.3%) cases, respectively. There was disagreement between the results in 37 (55.2%) of patients. Of these, 28 had greater infiltration in biopsies. The concordance (Kappa index) of biopsy with aspiration, imprint and flow cytometry was 0.501, 0.408 and 0.17; of aspiration with imprint and flow cytometry, it was 0.738 and 0.541 and between imprint and flow cytometry, it was 0.573%.

Conclusions: Only aspiration and imprint cytology results agreed. Biopsy showed greater infiltrations than the other methods, but aspiration, and imprint and flow cytometry provided additional data in the diagnosis and thus should also be performed.