Reticulocyte Parameters as Early Indicators of Hematopoietic Recovery after Bone marrow Transplantation

Abstract

The evaluation of hematopoietic recovery after myeloablative chemotherapy in bone marrow transplant patients is based on sequential peripheral blood cell counting; particularly the absolute neutrophil count (ANC) >0,5xl0⁹/l is the classical indicator of BM engraftment. The development of automated flow-cytometric analyzers has made available precise reticulocyte counts (RET) and the proportion of young, highly fluorescent reticulocytes (HFR) as accurate and early indices of haemopoietic recovery. We have studied 12 patients who received autologous PBSCT; peripheral blood mononuclear cells were collected after chemotherapy and rhG-CSF administration by repeated leukapheresis until a minimum of 4xl08 mononuclear cells. RET and percentage of HFR were obtained with the reticulocyte counter Sysmex-Toa R-1000. In our patients the three most useful indicators of BM recovery were HFR >5%, RET >20xl0⁹/l and ANC >0,5xl0⁹/l. Recovery of HFR >5% was obtained after a median time of 9 days, one day before recovery of RET and 4,5 days before recovery of ANC >0,5xl0⁹/l; the rise of HFR fraction was the earliest sign of engraftment in 91,7% of our patients. In conclusion, these three parameters show an excellent predictive value close to 100% for monitoring of BMT engraftment in PBSCT.

Hematopoietic regeneration after myeloablative radiochemotherapy for bone marrow transplantation (BMT) is monitored by sequential peripheral blood cell counting. Until recently the earliest practical measure of the onset of recovery was absolute neutrophil count (ANC)¹ Platelet count (PLT) is unreliable because of the many platelet transfusions given to most patients. Recent reports suggest that reticulocyte count (RET) performed by automated flow-cytometric methods is an early and accurate index of engraftment, especially if new indices which quantify the presence of young, highly fluorescent reticulocytes (HFR) are used.^4,5,8,10,14 A great heterogeneity of threshold values exists in the literature as far as RET and reticulocyte subfractions are concerned, which makes the comparison of results obtained by different authors extremely difficult. Moreover, the transplant of stem cells collected by leukapheresis from peripheral blood (PBSCT) is characterized by very fast ANC and PLT recovery^9,13,16, but RET and HFR have never been stdied in PBSCT patients.

The main objectives of our study were: 1) to define and compare the duration and characteristics of the hematopoietic suppression in PBSCT, in terms of peripheral blood cytopenia and supportive care requirements, in comparison with allo- and auto- BMT; 2) to determine the most suitable peripheral blood variables for the study of hematopoietic reconstitution; 3) to establish the clinical value of the selected variables in the monitoring of PBSCT patients.