Percentage of CD34 + Cells in a Minimum 500-Cell Count in Bone Marrow Trephines of Patients with Chronic Myeloid Leukaemia Provides the Best Correlation with Aspirate Blast Count.

We studied the expression of CD34 in 169 bone marrow trephines of 53 patients with CML in chronic, accelerated and blastic phases. The bone marrow blast count ranged from 0–82% (median: 4.5%). All were receiving imatinib treatment. We aimed to establish which counting method in bone marrow trephines provided the best correlation with the blast count of the corresponding bone marrow aspirate in all phases of the disease. Paraffin embedded sections were stained with the monoclonal antibody QBEND10.

CD34 expression in each marrow trephine was evaluated by three counting methods. The first method, established in our department for several years, expressed the percentage of CD34 positive cells vs. all nucleated cells in a minimum 500-cell count (% CD34+/500 cells). The second recorded the total number of CD34 positive cells in ten high power fields (CD34+/10hpf) using x 40 magnification /numerical aperture 0.65. The third method evaluated the highest number of CD34 positive cells present in a single high power field (CD34+/hpf), this value being taken from the previous 10 hpf count. The two latter methods were employed because they may be more applicable for general use by practicing histopathologists. In addition, counting over 10 hpf provides a much larger sample size than a 500-cell count. CD34 expression in endothelial cells served as a positive internal control.

All three methods showed significant positive correlation with blast count (% CD34+/500 cells: Pearson’s Correlation - 0.723, sig - <0.001; CD34+/10hpf: Pearson’s Correlation - 0.434, sig - <0.001; CD34+/hpf: Pearson’s Correlation - 0.372, sig - <0.001). In conclusion, our previously established method of recording the percentage of CD 34 positive cells vs. all nucleated cells in a minimum 500-cell count provided the best correlation with the blast count.