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Peripheral blood CD34/45+ cell (CD34/45) enumeration is an expensive and labour-intensive investigation but remains the standard assay for optimizing yield and timing of peripheral blood stem cell harvesting (PBSCH). The present study examined the value of the Sysmex SE9000 parameters (WBC, neutrophil count, and immature myeloid index (IMI)) and Sysmex R2000 reticulocyte parameters (absolute, high and medium fluorescence reticulocytes) in predicting the optimum timing of PBSCH in comparison to peripheral blood CD34/45. Sixty-four PBSCH from 23 patients with haematological malignancies were assessed with a variety of mobilization regimes used. Reticulocyte parameters showed high interpatient variability and did not prove clinically useful. IMI did not consistently predict satisfactory PBSCH yield except when > 1000 x 10(6)/l. Peripheral blood CD34/45 was the most useful predictor of yield. IMI > 20 x 10(6)/l was, however, a useful surrogate for predicting a rise in peripheral blood CD34/45 from nadir and proved to be superior to WBC or neutrophil count. A rising IMI is a marker of early regeneration and has a role in determining when to initiate enumeration of peripheral blood CD34/45.

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The pattern of emergence of multipotential (CFU-A) and committed (CFU-GM and BFU-E) progenitor cells in peripheral blood has been examined in patients with Hodgkin's disease and non-Hodgkin's lymphoma. Mobilization protocols used chemotherapy with or without granulocyte colony-stimulating factor (n=8 and n=5, respectively). In all patients, the numbers of CFU-A, CFU-GM and BFU-E peaked simultaneously, rather than sequentially, suggesting that marrow regeneration after these mobilization protocols occurred from progenitors at all stages of differentiation. We conclude that peripheral blood stem cell harvest strategies based on peak values for total progenitor numbers will also capture maximum numbers of multipotential progenitors. However, the variable relationship between CFU-A and CFU-GM numbers suggests that overall progenitor cell numbers can give only a broad estimate of the absolute numbers of multipotential progenitors in an individual harvest.