Actual (ABW) or Ideal (IBW) Body Weight to Calculate CD34+ Cell Dose in Patients Undergoing Autologous Hematopoietic Stem Cell Transplantation for Myeloma?

Abstract

CD34+ cell dose calculations for hematopoietic stem cell transplantation (HSCT) are usually based on actual body weight (ABW). We have shown that ideal body weight (IBW) provides a better basis for this in a small population of patients with hematologic malignancies (Ali et al. Bone Marrow Transplant 2003; 31:861–4). However, a concern has been raised that this may not be applicable in myeloma because of underestimation of IBW as a result of disease-related height loss (Maclean et al. Bone Marrow Transplant 2007; 40:665–9). We studied this relationship further in 514 myeloma autografts conditioned with 140 or 200 mg/m2 melphalan. The CD34+ cell doses (106/kg) by IBW and ABW were 1.37–39.36 (median 6.03) and 1.15–29.67 (median 4.84) respectively. The difference between ABW and IBW was −25 to +124% (median +26%). The analysis was performed for the entire group as well as after excluding outliers (engraftment before 8 or after 16 days).As Table 1 shows, IBW-based cell doses correlated better with engraftment than ABW-based (higher r2 and F):Table 1: Correlation between the CD34+ cell dose by IBW or ABW and various engraftment endpointsIBWABWEngraftment endpoint(109/L)r2FPr2FPAll patientsNeutrophils 0.50.832453<0.0010.822301<0.001Neutrophils 1.00.781818<0.0010.771738<0.001Platelets 200.54581<0.0010.53569<0.001Platelets 500.57610<0.0010.55584<0.001Selected (8–16 days)Neutrophils 0.5 (n=497)0.852715<0.0010.842523<0.001Neutrophils 1.0(n=468)0.852617<0.0010.842462<0.001Platelets 20(n=372)0.852215<0.0010.852027<0.001Platelets 50(n=214)0.851197<0.0010.841078<0.001As Table 2 shows, CD34+ cell doses based on IBW as well as ABW significantly affected engraftment when analyzed separately as continuous variables. However, when analyzed together, only the dose based upon IBW retained significance:IBWABWEngraftment endpoint (109/L)UnivariateMultivariateUnivariateMultivariateAll patientsANC 0.51.0471 (P<0.0001)1.0372 (P=0.18)1.0591(P<0.0001)1.0131 (P=0.71)ANC 1.01.0532 (P<0.0001)1.0753 (P=0.008)1.0606 (P<0.0001)0.9720 (P=0.42)PIT 201.0315 (P=0.0003)1.0643 (P=0.019)1.0319 (P=0.003)0.9603 (P=0.22)PLT 501.0436(P<0.0001)1.0889 (P=0.0006)1.0422(P=0.0001)0.9464 (P=0.075)Selected (8–1 6 days)ANC 0.51.0627 (P<0.0001)1.0478 (P=0.076)1.0793(P<0.0001)1.0198 (P=0.57)ANC 1.01.0687(P<0.0001)1.0785 (P=0.006)1.0826(P<0.0001)0.9874(P=0.73)PIT 201.0448 (P<0.0001)1.0453 (P=0.13)1.0538(P<0.0001)0.9993(P=0.99)PLT 501.0483(P<0.0001)1.0684(P=0.051)1.0535(P=0.0004)0.9746 (P=0.56)Table 2: Relationship between engraftment and the CD34+ cell dose analyzed as a continuous variable (risk ratio and P value)This observation is important in practice to avoid subjecting a patient to additional mobilization and apheresis procedures if the target cell dose has been met based on IBW. With increasing obesity (half the patients were >25% overweight), accounting for the correct weight is an important practical consideration. Infusion of an appropriate number of cells also allows for extra cells to be retained for possible future use.In this group, if every patient's height was underestimated by 1 inch (i.e. was increased by 1 inch for the purpose of calculations – assuming an element of kyphosis), IBW of men would have increased by 2.4–6.0% (median 3.2%) and IBW of women by 9.3–17.6% (median 12.4%). This suggests that implications of a height difference for calculating IBW in men are minimal but could be significant in women.We conclude that a CD34+ cell dose based on IBW is a better predictor of engraftment speed than one based on ABW, and IBW should be used as the basis for cell dose calculations in autologous HSCT. Any height loss, especially in myeloma patients, should be taken into account while calculating IBW for this purpose.