Two-color Flow Cytometry with a CD19 Gate for the Evaluation of Bone Marrow Involvement of B-cell Lymphoma

The usefulness of two-color flow cytometry with a CD19 gate (CD19-FCM) for detecting clonal B-cells in the bone marrow was evaluated. Since kappa and lambda ratios analyzed in the bone marrow from healthy adults were within the range of 0.5-3.0, outside of this range was regarded as the existence of clonal B-cells. Mixing experiments in vitro showed that 10% or more of clonal B-cells contaminating normal bone marrow cells could be detected using CD19-FCM. Ninety-nine bone marrow samples from 60 patients with B-cell lymphoma were simultaneously analyzed using CD19-FCM and histologic examination of both bone marrow aspiration and core needle biopsy samples. The agreement of results obtained by both examinations was 82% (81/99). Discrepant results were found in 18 samples of 10 patients. All except one sample were positive for CD19-FCM analysis but negative for histologic examination and the conversion of CD19-FCM-positivity to CD19-FCM-negativity was associated with chemotherapy. These results suggest that CD19-FCM is useful for the evaluation of bone marrow involvement of B-cell lymphoma.