| Definition |
A paticular kind of hematopoietic stem cell, used in bone marrow and stem cell transplantation. Range of CD34+ cells in the bone marrow can be 1-4%, while CD34+ cells in mobilized pheresis products can range from 0.1% (in a poor mobilizer) to more than 1%. The assay for CD34+ cells is a flow cytometric assay, and this technique is inherently inaccurate at the lowest percentages. This means that the number of CD34+ cells based on a measured frequency of 0.1% easily can be in error by a factor of 2 in either the direction of more or less cells. Remember this when assessing when to stop apheresis in patients with poor collections. In collections that have undergone CD34 selection, the CD34 purity is 40-90%, and these determinations are extremely accurate. Another consideration is that low CD34 PBSC collections often have a higher granulocyte content, which can complicate freezing and/or thawing and, therefore, have an impact on yield of cells actually infused after storage.
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