At what hemoglobin level is a transfusion triggered?

Updated: Apr 16, 2019
  • Author: Linda L Maerz, MD, FACS, FCCM; Chief Editor: Emmanuel C Besa, MD  more...
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Physiologic triggers, as elucidated above, are the most accurate predictors of transfusion requirements, as they are based on the patient’s specific needs with respect to deranged physiology. However, the desire to establish a generic "number to treat" with respect to hemoglobin and hematocrit has permeated transfusion practice. Much of the controversy surrounding transfusion practice paradigms centers on disagreement as to what constitutes the proverbial perfect number.

A quarter of a century ago, optimal treatment of surgical and critically ill patients targeted hemoglobin levels greater than or equal to 10 g/dL and hematocrit values greater than or equal to 30%. Subsequent understanding of the risks inherent in transfusion prompted investigations designed to reestablish a minimum baseline for acceptable hemoglobin concentrations.

At hemoglobin levels below 3.5-4 g/dL, mortality significantly increases in otherwise healthy patients. Work by Shander et al indicates decreased cognition with hemoglobin levels below 5 g/dL. [4] Additionally, Carson et al demonstrated that morbidity and/or mortality rises and becomes extremely high with postoperative hemoglobin levels below 5-6 g/dL. [5]

The American Society of Anesthesiologists uses hemoglobin levels of 6 g/dL as the trigger for required transfusion, although more recent data suggest decreased mortality with preanesthetic hemoglobin concentrations of greater than 8 g/dL, particularly in renal transplant patients. [6]

Restrictive transfusion strategies have been supported by the Transfusion Requirements in Critical Care (TRICC) trial, published in 1999, as well as others. The TRICC trial documented an overall trend toward decreased 30-day mortality and significantly decreased mortality among patients who were less acutely ill and among patients younger than 55 years in the group using a hemoglobin transfusion trigger of 7 g/dL compared with the more liberally transfused group. The investigators concluded that a restrictive transfusion strategy is at least as effective as and possibly superior to a liberal transfusion strategy in critically ill patients. The exception to this paradigm is patients with acute myocardial infarction and unstable angina.

The CRIT study, published in 2004, is a prospective, multiple center, observational cohort study of intensive care unit (ICU) patients in the United States, which investigated the relationship of anemia and RBC transfusion to clinical outcomes. The investigators found that the number of RBC units transfused is an independent predictor of worse clinical outcome. [7]

An updated 2016 Cochrane Database review reinforces these notions with respect to restrictive transfusion strategies.  This review summarizes good evidence that transfusion of allogeneic RBCs can safely be avoided in patients with hemoglobin levels above 7-8 g/dL. [8]

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