Criteria for marrow engraftment: comparison of reticulocyte maturity index with conventional parameters.

Reticulocyte maturity index (RMI) has recently been proposed as an early indicator of marrow engraftment. We compared the RMI with conventional bone marrow engraftment criteria including total leukocyte count (WBC), absolute neutrophil count (ANC), reticulocyte count (RC) and the day of last platelet transfusion required to maintain the platelet count (PC) > or = 20 x 10(9)/l in 37 patients undergoing allo- or autologous BMT. There was no discrepancy in predicting engraftment between RMI, ANC, WBC and RC. RMI indicated engraftment earlier (median day 17, range 10-63 days) than the ANC (median day 19, range 8-63 days), WBC (median day 19, 9-71), RC (median day 19, 11-125) or PC (median day 29, 11-237). RMI heralded engraftment preceded ANC, WBC, RC or PC in 22, 21, 34 and 32 patients, respectively. RMI signal occurred 6 days prior to the rise in ANC in patients who engrafted later than 25 days (n = 7). Trend analysis showed that ANC fluctuated more frequently (6/37 patients) than RMI (1/37). Combined use of ANC and RMI (whichever increased first) predicted engraftment earlier (median 15 days) and more confidently (no false starts) than either used alone.