Flow Cytometric Enumeration of Peripheral Blood CD34+ Cells Predicts Bone Marrow Pathology in Patients with Less Than 1% Blasts by Manual Count.

Background and aims: Significance of absolute number of CD34⁺ cells in the peripheral blood of patients with less than 1% myeloblasts by manual differential count is unknown and our aim is to study its relevance in clinical practice.

Methods: We studied 138 peripheral bloods flow cytometric analyses in patients with less than 1% myeloblasts by manual differential, when CD34⁺ events were present in the gate that encompassed lymphocytes, monocytes, stem cells, and blasts.

Results: The average absolute number of CD34⁺cells in the peripheral blood was 11 CD34⁺cells/µL ranging from less than 1 cell/µL to 147 cells/µL. The average absolute number of CD34⁺ cells in patients with an abnormal expansive process involving bone marrow (metastases, myelodysplasia, granulomas, marrow infections) or if bone marrow biopsy not performed, presumed expansive marrow process was 25 cells/µL, and in patients without an expansive marrow process (or presumed negative) was 4 cells/µL (P<0.00007). Cutoff 12 CD34⁺ cells/μL had 93% positive predictive value for bone marrow involvement by an expansive process and 78% negative predictive value.

Conclusion: Flow cytometric testing of the peripheral blood is extremely sensitive method for enumerating CD34⁺ cells and can detect fewer than one CD34⁺ cell/µL. The absolute number of CD34⁺ cells in the peripheral blood is a useful parameter in determining marrow involvement by an expansive process and may provide guidance with respect to the necessity for bone marrow biopsy.