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Blood, Vol. 91 No. 9 (May 1), 1998:
pp. 3509-3517
By
From the Epidemiology of Platelet Recovery Study Group and Genentech,
South San Francisco, CA.
An observational study was conducted at 18 transplant centers in the
United States and Canada to characterize the platelet recovery of
patients receiving myeloablative therapy and stem cell transplantation
and to determine the clinical variables influencing recovery, determine
platelet utilization and cost, and incidence of hemorrhagic events. The
study included 789 evaluable patients transplanted in 1995. Clinical,
laboratory, and outcome data were obtained from the medical records.
Variables associated with accelerated recovery in multivariate models
included (1) higher CD34 count; (2) higher platelet count at the start
of myeloablative therapy; (3) graft from an HLA-identical sibling
donor; and (4) prior stem cell transplant. Variables associated with
delayed recovery were (1) prior radiation therapy; (2) posttransplant
fever; (3) hepatic veno-occlusive disease; and (4) use of
posttransplant growth factors. Disease type also influenced recovery.
Recipients of peripheral blood stem cells (PBSC) had faster recovery
and fewer platelet transfusion days than recipients of bone marrow
(BM). The estimated average 60-day platelet transfusion cost per
patient was $4,000 for autologous PBSC and $11,000 for allogeneic BM
transplants. It was found that 11% of all patients had a significant
hemorrhagic event during the first 60 days posttransplant, contributing
to death in 2% of patients. In conclusion, clinical variables
influencing platelet recovery should be considered in the design and
interpretation of clinical strategies to accelerate recovery. Enhancing
platelet recovery is not likely to have a significant impact on 60-day mortality but could significantly decrease health care costs and potentially improve patient quality of life.
DESPITE RECENT advances in cytokine and
stem cell technology, platelet transfusions are still required to
support patients after myeloablative therapy and marrow (BM) or
peripheral blood stem cell (PBSC) transplantation. Platelet
transfusions are associated with morbidity related to transfusion
reactions, platelet alloimmunization and transfusion-associated viral
infections.1-3 In addition, the costs of platelet
transfusion support and management of related complications adds to the
costs of transplantation. Finally, prolonged thrombocytopenia may place
these patients at increased risk of life-threatening
hemorrhage.4,5 Effective strategies to enhance platelet
recovery could therefore benefit patients undergoing hematopoietic stem
cell transplantation (HSCT).
An understanding of the clinical variables influencing platelet
recovery would have an impact on clinical practice, as well as on the
design and interpretation of clinical trials examining such strategies.
Moreover, an estimation of the magnitude and cost of transfusion
utilization, as well as the incidence of hemorrhagic complications
associated with prolonged thrombocytopenia, may provide insight into
the potential benefits of a strategy to enhance platelet recovery.
To characterize the platelet recovery of patients after HSCT and to
identify key predictors of recovery, we conducted an
observational study at 18 transplant centers in the United States and
Canada. Platelet utilization, transfusion practices and costs, and
hemorrhagic events after HSCT were examined.
Study Design
Patient Population
Study Sample In this study, 980 consecutive patients were screened. A total of 119 patients were excluded because of (1) use of investigational agents that rendered outcome data proprietary (62 patients), (2) refusal to sign informed consent if so required by their institution (37 patients), and (3) data not adequately collected (20 patients).Data Collection Patient medical history as well as clinical, laboratory, and outcomes data were obtained from medical records. Patients were followed and data collected through posttransplant day 60. To determine predictors of recovery, two categories of variables were examined. The first were baseline predictors, those pretreatment variables known before the start of myeloablative therapy. The second were time-dependent predictors, variables occurring after the start of myeloablative therapy. Analyses of platelet utilization and cost were based on transfusion data. In this study, 6 U of random donor platelets were defined as equivalent to a single donor transfusion unit. A platelet transfusion event was defined as a single transfusion. Hemorrhagic events were recorded and their severity graded using Cancer and Leukemia Group B criteria (see Table 6). Posttransplant events such as hepatic veno-occlusive disease (VOD), disseminated intravascular coagulation (DIC), thrombotic microangiopathic hemolytic anemia, and graft-versus-host disease (GVHD) were recorded based on the clinical diagnoses made at the individual centers. GVHD was graded using the Seattle criteria.6
Definitions Platelet recovery to greater than 20,000/µL was defined as the day when the first of two consecutive platelet counts satisfied the following conditions: (1) both platelet counts were greater than 20,000/µL; (2) no platelet transfusion was given on or between the days of the two counts; (3) the second platelet count was at least as high as the first; (4) the two counts were 2 or more days apart or 1 day apart, with the next (third) count greater than or equal to the first count with no intervening platelet transfusions. Patients who died or who were lost to follow-up before achieving recovery were considered censored at the date of last reported platelet count. Neutrophil recovery was defined as the first of 2 consecutive days of an absolute neutrophil count (ANC) of greater than 500/µL. An alternative donor was defined as any donor who was not an HLA-identical sibling. The mononuclear cell count was defined as the number of monocytes and lymphocytes per kilogram; the total nucleated cell count was defined as the number of monocytes, lymphocytes, and polymorphonuclear cells per kilogram.Estimation of Platelet Transfusion Costs Platelet costs were based on 1996 charges from the Fred Hutchinson Cancer Research Center (Seattle, WA). A cost of $592 was applied for each single-donor apheresis unit: apheresis ($413), irradiation ($13), transport and handling ($10), tubing ($15), and hospital charges per transfusion ($141). A cost of $475 was applied for each 6-unit random donor platelet concentrate: platelet concentrates ($296) and charges for transport, handling, tubing, and hospital charges per transfusion, as described above.Statistical Methods Time to platelet recovery was summarized by transplant type and underlying disease using Kaplan-Meier estimates and log-rank tests. Multivariate proportional hazards models for platelet recovery were fit separately for the two largest transplant subgroups: autologous PBSC and allogeneic BM patients. Models were built in stages with the best baseline predictor model identified first, to which time-dependent predictors were added to obtain the final model. Variable selection at each stage proceeded as follows: all univariate predictors significant at = .1 were considered candidates for inclusion in the
multivariate model which was constructed using stepwise and best-subset
selection algorithms. Inclusion of a variable in the first multivariate
model required that it be significant at the = .05 level, or for
variables with strong prior evidence of explanatory power, the .1 level. Underlying disease was included in all models to mitigate
potential confounding. Missing value indicators were used for
predictors with 10% or more missing values to reduce loss of
observations during variable selection. Final models were summarized by
regression parameter estimates and standard errors and graphically
using covariate-adjusted recovery curves. Only those subjects included
in the largest diagnosis groups within each transplant class were
evaluable for analysis (autologous PBSC-355 patients; allogeneic BM-275
patients). By contrast, all subjects in each transplant class,
irrespective of diagnosis were included in analyses of platelet
utilization.
Patients Of the 789 evaluable patients, 456 underwent autologous and 333 allogeneic transplantation. Among autologous transplant patients, 355 (78%) received PBSC alone, 64 (14%) received BM alone, and 37 (8%) received both PBSC and BM. Among allogeneic transplant patients, 283 (85%) received BM alone, 43 (13%) received PBSC alone, and 7 (2%) received both PBSC and BM.
Platelet Recovery
Univariate analysis.
Variables associated with an accelerated recovery included a higher
platelet count at the start of myeloablative therapy, use of
chemotherapy for mobilizing stem cells, a higher CD34 count in the
graft, and having had a previous stem cell transplant (Table 4). Compared with breast cancer and
multiple myeloma, all other diseases were associated with a longer time
to recovery. Baseline variables associated with slower recovery
included the use of a radiation-containing preparative regimen and a
higher mononuclear cell count of the graft. For the time-dependent
variables, earlier neutrophil recovery was associated with faster
platelet recovery. Fever greater than 39°C and the presence of VOD
were associated with slower recovery.
Multivariate analysis.
Variables associated with accelerated recovery included a higher CD34
count of the graft (Fig 2), higher platelet
count at the start of myeloablative therapy, and having had a previous stem cell transplant (Table 5). Undergoing
radiation therapy before the myeloablative regimen was associated with
slower recovery. Compared with breast cancer, a diagnosis of leukemia,
non-Hodgkin's lymphoma (NHL), multiple myeloma, and Hodgkin's disease
(HD) was associated with a longer time to recovery. For the
time-dependent variables, posttransplant fever and VOD were associated
with a longer time to recovery.
Platelet Recovery
Univariate analysis.
Variables associated with an accelerated recovery included use of a
graft from an HLA-identical sibling donor and a higher total nucleated
cell count of the graft (Table 4). Compared with acute myeloid leukemia
(AML), all other diseases were associated with a shorter time to
recovery. Baseline variables associated with slower recovery included
any manipulation of the marrow graft, T-cell depletion, and the use of
a radiation-containing preparative regimen. For the time-dependent
variables, earlier neutrophil recovery was associated with faster
platelet recovery. The use of posttransplant growth factors, as well as
the presence of fever, VOD, and GVHD, was associated with slower
recovery.
Multivariate analysis.
The use of an HLA-identical sibling donor was strongly associated with
accelerated recovery (Table 5). Although not reaching statistical
significance, a higher total nucleated cell count of the graft was
associated with more rapid recovery. Patients with AML and
myelodysplastic syndromes had slower recovery than patients with
chronic myeloid leukemia. For the time-dependent variables, fever, VOD,
and the use of posttransplant growth factors were associated with a
longer time to recovery.
Platelet Recovery and Utilization by Stem Cell Source
Platelet Transfusion Practices
Financial Impact of Platelet Transfusions
Hemorrhagic Events Among the 789 evaluable patients, 143 hemorrhagic events of moderate or greater severity occurred in 89 patients, or 11% of the study population (Table 7). Most events occurred in patients undergoing allogeneic transplantation (78%), and before platelet recovery (89%). The median (range) time of hemorrhage from the date of stem cell infusion was 19 days (0 to 60). The major site of bleeding was genitourinary. In this regard, many of such events were related to chemotherapy-induced cystitis. Genitourinary prophylaxis routinely used by centers included mesna alone (1 center), hydration alone (6 centers), and both mesna and hydration (11 centers). The second most common site of bleeding was gastrointestinal. In this regard, 9 centers routinely used prophylactic H2 blockers. Most events (66%) occurred when the morning platelet count was greater than 20,000/µL. Sixteen patients, or 2% of the entire study population, died from a hemorrhagic event.
The time to platelet recovery after myeloablative therapy and HSCT is influenced both by baseline and time-dependent clinical variables. For autologous PBSC recipients, the CD34 content of the graft was the most significant variable associated with faster recovery. As both lineage-committed and uncommitted stem cells express CD34, its strength as a predictor was expected and confirms the findings of others.7-11 The impact of the other variables identified in the multivariate model on recovery were independent of the CD34 content of the graft. The pretreatment platelet count may act as a surrogate marker for the quality of the stem cell graft and microenvironment. The effect of disease may be related to differences in prior therapy and their impact on stem cells or to inherent biologic differences in the stem cell/microenvironment compartments. The influence of prior local radiation therapy may be the result of toxic effects of radiation on stem cells and marrow microenvironment.12 Finally, the association of faster recovery for recipients of a second autologous PBSC transplant is not intuitively obvious. Of the 18 patients who had a prior HSCT, however, 15 were from a single institution, all having a diagnosis of multiple myeloma, with the second transplant a planned part of the treatment strategy. Therefore, the impact of a prior HSCT on platelet recovery is probably attributable to confounding variables related to the clinical course and treatment plan of these patients, rather than to a true biologic effect.
Submitted August 25, 1997;
accepted December 22, 1997.
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