A further update on mortality and morbidity in patients with very low hemoglobin levels who decline blood transfusion.

BACKGROUND: In the past two decades, researchers have published mortality and morbidity rates in patients with very low hemoglobin levels declining blood transfusion. The clinical knowledge and tools available for the management of patients who decline transfusions have grown since these publications. The aim of our study was to provide a further update on outcomes associated with severe anemia in these patients. STUDY DESIGN AND METHODS: A retrospective observational study of patients declining allogeneic blood transfusions with nadir hemoglobin levels ≤8 g/dL treated at The Institute for Blood Management, HELIOS Klinikum Gotha, Germany. Outcomes were in-hospital mortality within 30 days and composite morbidity or mortality, with morbidity events defined as acute myocardial infarction, cardiac failure, wound infection, arrhythmia, and pneumonia. RESULTS: Between June 2008 and June 2021, The Institute for Blood Management treated 2841 admissions of which 159 (5.6%) recorded nadir hemoglobin levels ≤8 g/dL. Of these, five (3.1%) patients died in hospital within 30 days, including four (4.8%) patients admitted for surgical procedures and one (1.4%) medical admission. There was a significant increase in the unadjusted proportion of composite morbidity or mortality events with severity of nadir hemoglobin, with each gram decrease in hemoglobin associated with a 1.48 (95% confidence interval = 1.05-2.09; p = .025) times increase. CONCLUSION: Our comparatively lower proportion of patients reaching hemoglobin levels ≤8 g/dL and lower mortality rates suggest outcomes in patients with severe anemia is modifiable with the application of current patient blood management and bloodless medicine and surgery strategies.

Penny-wise and pound-foolish: the challenges of preoperative anaemia management.

The timely correction of anaemia before major surgery is important for optimising perioperative patient outcomes. However, multiple barriers have precluded the global expansion of preoperative anaemia treatment programmes, including misconceptions about the true cost/benefit ratio for patient care and health system economics. Institutional investment and buy-in from stakeholders could lead to significant cost savings through avoided complications of anaemia and red blood cell transfusions, and through containment of direct and variable costs of blood bank laboratories. In some health systems, billing for iron infusions could generate revenue and promote growth of treatment programmes. The aim of this work is to galvanise integrated health systems worldwide to diagnose and treat anaemia before major surgery.

Data and Metrics for Patient Blood Management: A Narrative Review and Practical Guide.

Data collection, analysis, and reporting are fundamental for a successful hospital-based patient blood management program; however, very little has been published on the topic. Our aim was to synthesize evidence from a literature review to provide a detailed, practical list of outcome metrics, and the required data collection(s) to inform implementation. Ovid MEDLINE and PubMed were searched for any full-text original research articles published from inception to the year 2020. We included any studies reporting the implementation of interventions or programs study authors defined as "patient blood management" and extracted information on data collected and metrics reported. We included 45 studies describing the implementation of a patient blood management program and/or strategies. The outcomes reported by these studies were grouped into 1 of 36 metrics. We compiled a list of 65 relevant data elements to collect, and their potential source hospital information systems: patient administration, laboratory, transfusion/blood bank, operating room, pharmacy, emergency department, and intensive care unit. We further categorized patient blood management data systems into basic, intermediate, and advanced based on the combination of different information systems sourced. The results of this review can be used to inform patient blood management programs in planning what data collection(s) are needed, where these data can be sourced from, and how they can be analyzed.

Hospital-Acquired Infection, Length of Stay, and Readmission in Elective Surgery Patients Transfused 1 Unit of Red Blood Cells: A Retrospective Cohort Study.

BACKGROUND: Most patients transfused red blood cells in elective surgery receive small volumes of blood, which is likely to be discretionary and avoidable. We investigated the outcomes of patients who received a single unit of packed red blood cells during their hospital admission for an elective surgical procedure when compared to those not transfused. METHODS: This retrospective cohort study included elective surgical admissions to 4 hospitals in Western Australia over a 6-year period. Participants were included if they were at least 18 years of age and were admitted for elective surgery between July 2014 and June 2020. We compared outcomes of patients who had received 1 unit of red blood cells to patients who had not been transfused. To balance differences in patient characteristics, we weighted our multivariable regression models using the inverse probability of treatment. In addition to propensity score weighting, our multivariable regression models adjusted for hemoglobin level, surgical procedure, patient age, gender, comorbidities, and the transfusion of fresh-frozen plasma or platelets. Outcomes studied were hospital-acquired infection, hospital length of stay, and all-cause emergency readmissions within 28 days. RESULTS: Overall, 767 (3.2%) patients received a transfusion of 1 unit of red blood cells throughout their admission. In the propensity score weighted analysis, the transfusion of a single unit of red blood cells was associated with higher odds of hospital-acquired infection (odds ratio, 3.94; 95% confidence interval [CI], 2.99-5.20; P < .001). Patients who received 1 unit of red blood cells throughout their admission were more likely to have a longer hospital stay (rate ratio, 1.57; 95% CI, 1.51-1.63; P < .001) and had 1.42 (95% CI, 1.20-1.69; P < .001) times higher odds of 28-day readmission. CONCLUSIONS: These results suggest that avoidance of even small volumes of packed red blood cells may prevent adverse clinical outcomes. This may encourage hospital administrators to implement strategies to avoid the transfusion of even small volumes of red blood cells by applying patient blood management practices.

Physician autonomy and patient rights: lessons from an enforced blood transfusion and the role of patient blood management.

This article provides an ethical and medico-legal analysis of ruling no. 465 of 30 May 2018 issued by the Court of Termini Imerese (Palermo) and confirmed on appeal on 11 November 2020, which, in the absence of similar historical precedents in Europe, convicted a medical doctor of a crime of violent assault for having ordered the administration of a blood transfusion to a patient specifically declining blood transfusion on religious grounds. We analyse the Court's decision regarding the identification of assault in performing the blood transfusion and its decision not to accept exculpatory urgent 'necessity' as a defence. In addition, we present an updated revision of the current standard of care in transfusion medicine as well as the ethical principles governing the patient's declining of transfusion. In doing so, we highlight that respect for the patient's self-determination in declining transfusions and respect for the professional autonomy of the doctor protecting the safety and life of the patient could be equally satisfied by applying the current peer-reviewed evidence.

Associations of a Preoperative Anemia and Suboptimal Iron Stores Screening and Management Clinic in Colorectal Surgery With Hospital Cost, Reimbursement, and Length of Stay: A Net Cost Analysis.

BACKGROUND: In 2016, a preoperative clinic was implemented to screen, evaluate, and manage anemia and suboptimal iron stores at a major tertiary care medical center in Western Australia. Few studies compare the costs and reimbursements associated with preoperative anemia and suboptimal iron stores management. The objective of our study was to conduct a net cost analysis associated with the implementation of this clinic. METHODS: We designed a retrospective cohort study involving elective colorectal surgical admissions over a 3-year period. The baseline year selected was the 2015-2016 financial year, with outcomes in the 2016-2017 and 2017-2018 year compared to baseline. The study perspective was the Western Australian Health System. Hospital costs were extracted from the health service clinical costing system, which captures costs at the admission level. The primary outcome was net cost, defined as gross cost minus reimbursement (or funding) received. RESULTS: Our 3-year study included 544 admissions for elective colorectal surgery. After the implementation of the preoperative clinic, 73.4% (n = 257) of admissions were screened for anemia and suboptimal iron stores, and 31.4% (n = 110) received intravenous iron. In our adjusted analysis, when comparing the final year (2017-2018) with baseline (2015-2016), the units of red blood cells transfused per admission decreased 53% (142 vs 303 units per 1000 discharges; P = .006), and mean hospital length of stay decreased 15% (7.7 vs 9.1 days; P = .008). When comparing the final year with baseline, rectal resection admissions were associated with a mean decrease in the net cost of Australian dollar (A$) 7619 (95% confidence interval, 4230-11,008; P < .001) between 2015-2016 and 2017-2018. For small and large bowel procedures, there was a mean decrease of A$6744 (95% confidence interval, 2430-11,057; P = .002). CONCLUSIONS: The implementation of a preoperative anemia and suboptimal iron stores screening and management clinic in elective colorectal surgery was associated with reductions in red cell transfusions, length of stay, and net costs.

Systematic reviews and meta-analyses comparing mortality in restrictive and liberal haemoglobin thresholds for red cell transfusion: an overview of systematic reviews.

BACKGROUND: There are no overviews of systematic reviews investigating haemoglobin thresholds for transfusion. This is important as the literature on transfusion thresholds has grown considerably in recent years. Our aim was to synthesise evidence from systematic reviews and meta-analyses of the effects of restrictive and liberal transfusion strategies on mortality. METHODS: This was a systematic review of systematic reviews (overview). We searched MEDLINE, Embase, Web of Science Core Collection, PubMed, Google Scholar, and the Joanna Briggs Institute EBP Database, from 2008 to 2018. We included systematic reviews and meta-analyses of randomised controlled trials comparing mortality in patients assigned to red cell transfusion strategies based on haemoglobin thresholds. Two independent reviewers extracted data and assessed methodological quality. We assessed the methodological quality of included reviews using AMSTAR 2 and the quality of evidence pooled using an algorithm to assign GRADE levels. RESULTS: We included 19 systematic reviews reporting 33 meta-analyses of mortality outcomes from 53 unique randomised controlled trials. Of the 33 meta-analyses, one was graded as high quality, 15 were moderate, and 17 were low. Of the meta-analyses presenting high- to moderate-quality evidence, 12 (75.0%) reported no statistically significant difference in mortality between restrictive and liberal transfusion groups and four (25.0%) reported significantly lower mortality for patients assigned to a restrictive transfusion strategy. We found few systematic reviews addressed clinical differences between included studies: variation was observed in haemoglobin threshold concentrations, the absolute between group difference in haemoglobin threshold concentration, time to randomisation (resulting in transfusions administered prior to randomisation), and transfusion dosing regimens. CONCLUSIONS: Meta-analyses graded as high to moderate quality indicate that in most patient populations no difference in mortality exists between patients assigned to a restrictive or liberal transfusion strategy. TRIAL REGISTRATION: PROSPERO CRD42019120503.

Machine learning-based prediction of transfusion.

BACKGROUND: The ability to predict transfusions arising during hospital admission might enable economized blood supply management and might furthermore increase patient safety by ensuring a sufficient stock of red blood cells (RBCs) for a specific patient. We therefore investigated the precision of four different machine learning-based prediction algorithms to predict transfusion, massive transfusion, and the number of transfusions in patients admitted to a hospital. STUDY DESIGN AND METHODS: This was a retrospective, observational study in three adult tertiary care hospitals in Western Australia between January 2008 and June 2017. Primary outcome measures for the classification tasks were the area under the curve for the receiver operating characteristics curve, the F1 score, and the average precision of the four machine learning algorithms used: neural networks (NNs), logistic regression (LR), random forests (RFs), and gradient boosting (GB) trees. RESULTS: Using our four predictive models, transfusion of at least 1 unit of RBCs could be predicted rather accurately (sensitivity for NN, LR, RF, and GB: 0.898, 0.894, 0.584, and 0.872, respectively; specificity: 0.958, 0.966, 0.964, 0.965). Using the four methods for prediction of massive transfusion was less successful (sensitivity for NN, LR, RF, and GB: 0.780, 0.721, 0.002, and 0.797, respectively; specificity: 0.994, 0.995, 0.993, 0.995). As a consequence, prediction of the total number of packed RBCs transfused was also rather inaccurate. CONCLUSION: This study demonstrates that the necessity for intrahospital transfusion can be forecasted reliably, however the amount of RBC units transfused during a hospital stay is more difficult to predict.

Patient blood management: The best approach to transfusion medicine risk management.

In advanced health systems it is increasingly important to offer effective medical services that have high quality and safety standards. We present an overview of the direct hazards and the indirect hazards associated with blood transfusions. Our aim is to focus on the potential medico-legal impacts of these hazards in the context of clinical risk management, incorporating the accumulating evidence from Patient Blood Management programs. The direct or deterministic hazards of transfusion refer to scenarios where the mechanisms for post transfusion damage are clearly traceable to the blood transfused in a 1:1 cause and effect manner. The indirect hazards can be defined as probabilistic and are associated with transfusion through epidemiological studies. The implementation of Patient Blood Management programs demonstrates that the use of a blood transfusion is not always necessary or unavoidable but can be considered modifiable. Review of the literature confirms that transfusion should not be the default option to manage anemia or blood loss. Instead, accumulating evidence demonstrates that a patient-centred, proactive approach to managing a patient's own blood is the new standard of care. It thus follows, an adverse transfusion event, where the transfusion was avoidable through the application of patient blood management, may constitute a profile for medical professional medical negligence. In an effort to maximise patient safety, transfusion medicine practice culture needs to shift towards a patient blood management approach, with hospitals implementing it as an important tool to minimize the risks of allogeneic blood transfusion.

Essential Role of Patient Blood Management in a Pandemic: A Call for Action.

The World Health Organization (WHO) has declared coronavirus disease 2019 (COVID-19), the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a pandemic. Global health care now faces unprecedented challenges with widespread and rapid human-to-human transmission of SARS-CoV-2 and high morbidity and mortality with COVID-19 worldwide. Across the world, medical care is hampered by a critical shortage of not only hand sanitizers, personal protective equipment, ventilators, and hospital beds, but also impediments to the blood supply. Blood donation centers in many areas around the globe have mostly closed. Donors, practicing social distancing, some either with illness or undergoing self-quarantine, are quickly diminishing. Drastic public health initiatives have focused on containment and "flattening the curve" while invaluable resources are being depleted. In some countries, the point has been reached at which the demand for such resources, including donor blood, outstrips the supply. Questions as to the safety of blood persist. Although it does not appear very likely that the virus can be transmitted through allogeneic blood transfusion, this still remains to be fully determined. As options dwindle, we must enact regional and national shortage plans worldwide and more vitally disseminate the knowledge of and immediately implement patient blood management (PBM). PBM is an evidence-based bundle of care to optimize medical and surgical patient outcomes by clinically managing and preserving a patient's own blood. This multinational and diverse group of authors issue this "Call to Action" underscoring "The Essential Role of Patient Blood Management in the Management of Pandemics" and urging all stakeholders and providers to implement the practical and commonsense principles of PBM and its multiprofessional and multimodality approaches.

Patients with multiple myeloma over a large catchment of 2.5 million square kilometres: a Western Australia retrospective survival review.

Multiple myeloma is an incurable malignancy of plasma cells. We retrospectively reviewed the survival outcomes of patients with multiple myeloma in Western Australia (WA) public hospitals over a 10-year period. We did not detect a difference in survival between patients residing the metropolitan Perth and regional areas, despite a paucity of haematology services in regional WA due to low population density in a large geographic area. Patients with R-ISS Stage 3 had the poorest survival in our cohort with median survival of 24 months.

Multimodal Patient Blood Management Program Based on a Three-pillar Strategy: A Systematic Review and Meta-analysis.

OBJECTIVES: To determine whether a multidisciplinary, multimodal Patient Blood Management (PBM) program for patients undergoing surgery is effective in reducing perioperative complication rate, and thereby is effective in improving clinical outcome. BACKGROUND: PBM is a medical concept with the focus on a comprehensive anemia management, to minimize iatrogenic (unnecessary) blood loss, and to harness and optimize patient-specific physiological tolerance of anemia. METHODS: A systematic review and meta-analysis was performed. Eligible studies had to address each of the 3 PBM pillars with at least 1 measure per pillar, for example, preoperative anemia management plus cell salvage plus rational transfusion strategy. The study protocol has been registered with PROSPERO (CRD42017079217). RESULTS: Seventeen studies comprising 235,779 surgical patients were included in this meta-analysis (100,886 pre-PBM group and 134,893 PBM group). Implementation of PBM significantly reduced transfusion rates by 39% [risk ratio (RR) 0.61, 95% confidence interval (CI) 0.55-0.68, P < 0.00001], 0.43 red blood cell units per patient (mean difference -0.43, 95% CI -0.54 to -0.31, P < 0.00001), hospital length of stay (mean difference -0.45, 95% CI -0.65 to -0.25, P < 0,00001), total number of complications (RR 0.80, 95% CI 0.74-0.88, P <0.00001), and mortality rate (RR 0.89, 95% CI 0.80-0.98, P = 0.02). CONCLUSIONS: Overall, a comprehensive PBM program addressing all 3 PBM pillars is associated with reduced transfusion need of red blood cell units, lower complication and mortality rate, and thereby improving clinical outcome. Thus, this first meta-analysis investigating a multimodal approach should motivate all executives and health care providers to support further PBM activities.

Anemia in hospitalized patients: an overlooked risk in medical care.

BACKGROUND: This study investigated the association between nadir anemia and mortality and length of stay (LOS) in a general population of hospitalized patients. STUDY DESIGN AND METHODS: A retrospective cohort study of tertiary hospital admissions in Western Australia between July 2010 and June 2015. Outcome measures were in-hospital mortality and LOS. RESULTS: Of 80,765 inpatients, 45,675 (56.55%) had anemia during admission. Mild and moderate/severe anemia were independently associated with increased in-hospital mortality (odds ratio [OR] 1.5, 95% confidence interval [CI] 1.36-1.86, p = 0.001; OR 2.77, 95% CI 2.32-3.30, p < 0.001, respectively). Anemia was also associated with increased LOS, demonstrating a larger effect in emergency (mild anemia-incident rate ratio [IRR] 1.52, 95% CI 1.48-1.56, p < 0.001; moderate/severe anemia-IRR 2.18, 95% CI 2.11-2.26, p < 0.001) compared to elective admissions (mild anemia-IRR 1.30, 95% CI 1.21-1.41, p < 0.001; moderate/severe anemia-IRR 1.69, 95% CI 1.55-1.83, p < 0.001). LOS was longer in patients who developed anemia during admission compared to those who had anemia on admission (IRR 1.13, 95% CI 1.10-1.17, p < 0.001). Red cell transfusion was independently associated with 2.23 times higher odds of in-hospital mortality (95% CI 1.89-2.64, p < 0.001) and 1.31 times longer LOS (95% CI 1.25-1.37, p < 0.001). CONCLUSION: More than one-third of patients not anemic on admission developed anemia during admission. Even mild anemia is independently associated with increased mortality and LOS; however, transfusion to treat anemia is an independent and additive risk factor.

Blood use in patients receiving intensive chemotherapy for acute leukemia or hematopoietic stem cell transplantation: the impact of a health system-wide patient blood management program.

BACKGROUND: Little is published on patient blood management (PBM) programs in hematology. In 2008 Western Australia announced a health system-wide PBM program with PBM staff appointments commencing in November 2009. Our aim was to assess the impact this program had on blood utilization and patient outcomes in intensive chemotherapy for acute leukemia or hematopoietic stem cell transplantation. STUDY DESIGN AND METHODS: A retrospective study of 695 admissions at two tertiary hospitals receiving intensive chemotherapy for acute leukemia or undergoing hematopoietic stem cell transplantation between July 2010 and December 2014 was conducted. Main outcomes included pre-red blood cell (RBC) transfusion hemoglobin (Hb) levels, single-unit RBC transfusions, number of RBC and platelet (PLT) units transfused per admission, subsequent day case transfusions, length of stay, serious bleeding, and in-hospital mortality. RESULTS: Over the study period, the mean RBC units transfused per admission decreased 39% from 6.1 to 3.7 (p < 0.001), and the mean PLT units transfused decreased 35% from 6.3 to 4.1 (p < 0.001), with mean RBC and PLT units transfused for follow-up day cases decreasing from 0.6 to 0.4 units (p < 0.001). Mean pre-RBC transfusion Hb level decreased from 8.0 to 6.8 g/dL (p < 0.001), and single-unit RBC transfusions increased 39% to 67% (p < 0.001). This reduction represents blood product cost savings of AU$694,886 (US$654,007). There were no significant changes in unadjusted or adjusted length of stay, serious bleeding events, or in-hospital mortality over the study. CONCLUSION: The health system-wide PBM program had a significant impact, reducing blood product use and costs without increased morbidity or mortality in patients receiving intensive chemotherapy for acute leukemia or hematopoietic stem cell transplantation.

Improved outcomes and reduced costs associated with a health-system-wide patient blood management program: a retrospective observational study in four major adult tertiary-care hospitals.

BACKGROUND: Patient blood management (PBM) programs are associated with improved patient outcomes, reduced transfusions and costs. In 2008, the Western Australia Department of Health initiated a comprehensive health-system-wide PBM program. This study assesses program outcomes. STUDY DESIGN AND METHODS: This was a retrospective study of 605,046 patients admitted to four major adult tertiary-care hospitals between July 2008 and June 2014. Outcome measures were red blood cell (RBC), fresh-frozen plasma (FFP), and platelet units transfused; single-unit RBC transfusions; pretransfusion hemoglobin levels; elective surgery patients anemic at admission; product and activity-based costs of transfusion; in-hospital mortality; length of stay; 28-day all-cause emergency readmissions; and hospital-acquired complications. RESULTS: Comparing final year with baseline, units of RBCs, FFP, and platelets transfused per admission decreased 41% (p < 0.001), representing a saving of AU$18,507,092 (US$18,078,258) and between AU$80 million and AU$100 million (US$78 million and US$97 million) estimated activity-based savings. Mean pretransfusion hemoglobin levels decreased 7.9 g/dL to 7.3 g/dL (p < 0.001), and anemic elective surgery admissions decreased 20.8% to 14.4% (p = 0.001). Single-unit RBC transfusions increased from 33.3% to 63.7% (p < 0.001). There were risk-adjusted reductions in hospital mortality (odds ratio [OR], 0.72; 95% confidence interval [CI], 0.67-0.77; p < 0.001), length of stay (incidence rate ratio, 0.85; 95% CI, 0.84-0.87; p < 0.001), hospital-acquired infections (OR, 0.79; 95% CI, 0.73-0.86; p < 0.001), and acute myocardial infarction-stroke (OR, 0.69; 95% CI, 0.58-0.82; p < 0.001). All-cause emergency readmissions increased (OR, 1.06; 95% CI, 1.02-1.10; p = 0.001). CONCLUSION: Implementation of a unique, jurisdiction-wide PBM program was associated with improved patient outcomes, reduced blood product utilization, and product-related cost savings.

Impact of a Patient Blood Management Program and an Outpatient Anemia Management Protocol on Red Cell Transfusions in Oncology Inpatients and Outpatients.

BACKGROUND: Patient blood management (PBM) programs are associated with reduced transfusion usage, reduced hospital costs, and improved patient outcomes. The application of PBM principles in patients with malignant disease might achieve similar results. However, this population presents unique challenges. The aim of the present study was to investigate the impact of a PBM program on blood usage and patient outcomes in cancer patients, particularly in the setting of restricted use of erythropoiesis-stimulating agents (ESAs). MATERIALS AND METHODS: A retrospective observational study was performed of patients admitted with a primary diagnosis of malignancy treated at Eastern Maine Medical Center as inpatients or outpatients, or both, from January 2008 through July 2013. RESULTS: The proportion of inpatients and outpatients receiving ESAs decreased from 2.9% in 2008 to 1.1% in 2013 (p < .001). During the same period, an increase occurred in the mean dose of intravenous (IV) iron from 447 mg (95% confidence interval [CI], 337-556) to 588 mg (95% CI, 458-718). The mean red blood cell (RBC) units transfused per inpatient and outpatient episode decreased from 0.067 to 0.038 unit (p < .001). In inpatients, significant increases occurred in the proportion of single-unit RBC transfusions (p < .001) and patients infused with IV iron (p = .02), and significant decreases in the mean pretransfusion hemoglobin (p = .02) and RBC transfusion rate (p = .04). In-hospital mortality and length of stay did not change significantly during this period. CONCLUSION: Despite the decreased use of ESA therapy, the implementation of a PBM program and outpatient anemia management protocol in cancer patients at our medical center was associated with significant reductions in RBC usage.

Observational studies - should we simply ignore them in assessing transfusion outcomes?

BACKGROUND: As defined by evidence-based medicine randomized controlled trials rank higher than observational studies in the hierarchy of clinical research. Accordingly, when assessing the effects of treatments on patient outcomes, there is a tendency to focus on the study method rather than also appraising the key elements of study design. A long-standing debate regarding findings of randomized controlled trials compared with those of observational studies, their strengths and limitations and questions regarding causal inference, has recently come into focus in relation to research assessing patient outcomes in transfusion medicine. DISCUSSION: Observational studies are seen to have limitations that are largely avoided with randomized controlled trials, leading to the view that observational studies should not generally be used to inform practice. For example, observational studies examining patient outcomes associated with blood transfusion often present higher estimates of adverse outcomes than randomized controlled trials. Some have explained this difference as being a result of observational studies not properly adjusting for differences between patients transfused and those not transfused. However, one factor often overlooked, likely contributing to these variances between study methods is different exposure criteria. Another common to both study methods is exposure dose, specifically, measuring units transfused during only a part of the patient's hospital stay. When comparing the results of observational studies with randomized controlled trials assessing transfusion outcomes it is important that one consider not only the study method, but also the key elements of study design. Any study, regardless of its method, should focus on accurate measurement of the exposure and outcome variables of interest. Failure to do so may subject the study, regardless of its type, to bias and the need to interpret the results with caution.