Red cell transfusion "trigger": a review. (Review Article).Abstract: Despite the publication of several consensus guidelines that set forth recommendations for the transfusion of red cells, actual clinical practice continues to vary widely. Animal data and studies in human volunteers and patients support a red cell transfusion threshold of 7 to 8 g/dl in most patients. However, conflicting data, particularly in cardiac patients and in the elderly, suggest that it may be impossible to define a single red cell "trigger" for all patients. A well-designed, randomized ran·dom·ize tr.v. ran·dom·ized, ran·dom·iz·ing, ran·dom·iz·es To make random in arrangement, especially in order to control the variables in an experiment. , controlled trial controlled trial Clinical research A clinical study in which one group of participants receives an experimental drug while the other receives either a placebo or an approved–'gold standard' therapy. See Blinding, Double-blinded. is still needed to establish a safe threshold for red cell transfusion in adults with coronary artery disease coronary artery disease, condition that results when the coronary arteries are narrowed or occluded, most commonly by atherosclerotic deposits of fibrous and fatty tissue. . Key Words: red cell, threshold, transfusion, trigger ********** Like any other drug, it is axiomatic ax·i·o·mat·ic also ax·i·o·mat·i·cal adj. Of, relating to, or resembling an axiom; self-evident: "It's axiomatic in politics that voters won't throw out a presidential incumbent unless they think his challenger will that red cells should be administered only when clinically necessary and then in the minimal effective dose. However, because blood components are biologic products, indications for their use and optimal dosing have remained elusive. In the past decade, a number of guidelines have been promulgated prom·ul·gate tr.v. prom·ul·gat·ed, prom·ul·gat·ing, prom·ul·gates 1. To make known (a decree, for example) by public declaration; announce officially. See Synonyms at announce. 2. for the transfusion of red cells. (1-6) Although there is general agreement that red cells should be transfused only to improve oxygen-carrying capacity, considerable variability in clinical transfusion practice nonetheless remains. (7-9) These consensus guidelines suggest that transfusion to a hemoglobin level above 10 g/dl is rarely indicated, that when the hemoglobin falls below 7 to 8 g/dl even healthy young patients may require transfusion, and that normovolemic patients with symptomatic anemia should undergo transfusion regardless of hemoglobin concentration. (1-6) When the hemoglobin falls to between 7 and 10 g/dl in an asymptomatic patient, however, decision making with r egard to whether to transfuse trans·fuse v. To administer a transfusion of or to. trans·fus  a·ble adj. becomes murkier.
The quest to define a minimum threshold hemoglobin concentration at which patients achieve significant (net) benefit from transfusion of red cells is driven by patient safety concerns. First is the desire to minimize exposure to infectious agents, primarily (although not exclusively) transfusion-transmissible viruses. As viral risk is lowered, however, more attention is focused on red cell supply issues and the potential that red cell demand may outpace the supply of units. In addition, there is concern that transfusion-related immunomodulation might result in immunosuppression immunosuppression Suppression of immunity with drugs, usually to prevent rejection of an organ transplant. Its aim is to allow the recipient to accept the organ permanently with no unpleasant side effects. , increasing the likelihood of infection and/or cancer recurrence in red cell recipients. (10,11) Another issue to consider is that relatively high hemoglobin levels may in fact be detrimental to the patient, resulting in microcirculatory complications. (12-14) Animal Data Studies in dogs and baboons have shown that normal animals are capable of tolerating hemoglobin levels as low as 3 to 5 g/dl without adverse effects. (15-19) When dogs with experimentally induced critical coronary stenosis were subjected to isovolemic hemodilution, however, ischemic Ischemic An inadequate supply of blood to a part of the body, caused by partial or total blockage of an artery. Mentioned in: Antiangiogenic Therapy, Subarachnoid Hemorrhage, Ventricular Fibrillation ischemic electrocardiographic electrocardiographic emanating from or pertaining to electrocardiography. electrocardiographic monitoring maintenance of a more or less continuous surveillance of a patient's cardiac status by means of electrocardiography. (EGG) changes and deterioration of cardiac function became evident at hemoglobin levels between 6 and 7 g/dl (hematocrit Hematocrit Definition The hematocrit measures how much space in the blood is occupied by red blood cells. It is useful when evaluating a person for anemia. Purpose Blood is made up of red and white blood cells, and plasma. , 20%). (20) This effect was magnified in dogs with left ventricular hypertrophy left ventricular hypertrophy Cardiology Enlargement of the left ventricle often linked to the prolonged hemodynamic stress of CHF, characterized by myocardial cell hypertrophy, ↑ left ventricular wall thickness, ↓ ventricular compliance, ↑ . (21) Likewise, in dogs with critical coronary stenosis, evidence of contractile contractile /con·trac·tile/ (kon-trak´til) able to contract in response to a suitable stimulus. con·trac·tile adj. Capable of contracting or causing contraction, as a tissue. dysfunction developed when the hemoglobin fell below a mean of 7.5 g/dl, with marked dysfunction becoming apparent at mean hemoglobin levels of 6 g/dl. Transfusion to raise hemoglobin restored both contractile function and oxygen extraction in this trial. (22) Studies in Human Volunteers Similar experimental results have been reported in 32 normal human volunteers in whom acute isovolemic reduction of hemoglobin concentration to 5 g/dl did not result in inadequate critical oxygen transport. No clinically significant changes were seen in oxygen consumption or plasma lactate Lactate A salt or ester of lactic acid (CH3CHOHCOOH). In lactates, the acidic hydrogen of the carboxyl group has been replaced by a metal or an organic radical. Lactates are optically active, with a chiral center at carbon 2. levels, and only one patient demonstrated ST-segment T-wave changes in online EGG monitoring. The difficulty in determining the extent to which anemia can be tolerated safely is illustrated in the appearance of ischemic changes on Holter monitoring Holter Monitoring Definition Holter monitoring is continuous monitoring of the electrical activity of a patient's heart muscle (electrocardiography) for 24 hours, using a special portable device called a Holter monitor. in one patient without apparent preexisting pre·ex·ist or pre-ex·ist v. pre·ex·ist·ed, pre·ex·ist·ing, pre·ex·ists v.tr. To exist before (something); precede: Dinosaurs preexisted humans. v.intr. cardiovascular disease Cardiovascular disease Disease that affects the heart and blood vessels. Mentioned in: Lipoproteins Test cardiovascular disease . (23) Similarly, a recent small study (n = 9) of isovolemic hemodilution in healthy human volunteers demonstrated normal cognitive function cognitive function Neurology Any mental process that involves symbolic operations–eg, perception, memory, creation of imagery, and thinking; CFs encompasses awareness and capacity for judgment at a hemoglobin concentration as low as 7 g/dl but subtle changes in cognitive function with lower hemoglobin levels (reversible with autologous transfusion autologous transfusion Autologous blood transfusion Transfusion medicine The collection and re-infusion of the Pt's own blood and/or blood products; the volume of blood available for AT can be ↑ with recombinant erythropoietin and iron supplements; AT is most back to 7 g/dl). (24) Human Patient Data Studies in human patients have also yielded conflicting results and have failed to define an unequivocal transfusion trigger transfusion trigger Transfusion threshold Transfusion medicine The Hct and Hb values at or below which packed red cells are usually ordered for transfusion by a clinician; the most widely used current TT is a Hb of 70 g/L, after an NIH consensus = conference; lower . Retrospective studies of the consequences of anemia in patients who refused transfusion on religious grounds found that operative mortality operative mortality The percentage of Pts who die while hospitalized during or after a surgical procedure was inversely related to preoperative pre·op·er·a·tive adj. Preceding a surgical operation. preoperative preceding an operation. preoperative care the preparation of a patient before operation. hemoglobin and, not surprisingly, was significantly related to intraoperative blood loss. (25) Indeed, in this population, the negative impacts of a low preoperative hemoglobin and substantial intraoperative blood loss on postoperative survival were significantly magnified in patients with underlying cardiovascular disease (P = 0.03). (26) Numerous reports have indicated, however, that patients who are members of the Jehovah's Witnesses (JW) faith are capable of surviving hemoglobin levels as low as 5 g/dl (hematocrit, 15%). (27,28) Likewise, in two small prospective studies (n = 7 and 8, respectively) involving coronary artery bypass graft coronary artery bypass graft n. Abbr. CABG A surgical procedure in which a section of vein or other conduit is grafted between the aorta and a coronary artery below the region of an obstruction in that artery. patients without religious objections to transfusion, normovolemic hemodilution to a hematocrit of l5% was well tolerated during surgery, (29) without evidence of myocardial ischemia myocardial ischemia, n a loss of oxygen to the heart muscle caused by blockage of the coronary arteries or their branches. myocardial ischemia on electrocardiogram electrocardiogram /elec·tro·car·dio·gram/ (-kahr´de-o-gram?) a graphic tracing of the variations in electrical potential caused by the excitation of the heart muscle and detected at the body surface. and without affecting either lactate extraction or hypoxanthine hypoxanthine /hy·po·xan·thine/ (-zan´then) a purine base formed as an intermediate in the degradation of purines and purine nucleosides to uric acid and in the salvage of free purines. Complexed with ribose it is inosine. release. (30) Reported mortality rates in JW patients undergoing surgery are low (ranging from 0.1% (31) to l4% (32)) and, overall, both morbidity and mortality Morbidity and Mortality can refer to:
Cardiac Patients and the Elderly Data regarding the general population are equally conflicting and similarly fail to define a transfusion trigger. A large, retrospective, cohort study in elderly orthopedic patients undergoing surgical repair of hip fractures found no increase in likelihood of death in patients with hemoglobin levels as low as 8 g/dl who did not undergo transfusion compared with those who received red cells. (34) In fact, Spiess et al, (35) in a prospective, observational study of 2,202 patients undergoing coronary bypass coronary bypass Surgical treatment for coronary heart disease to relieve angina pectoris and prevent heart attacks. It became widely used in the 1960s. One or more blood vessels—usually an artery in the chest or a vein from the leg—are transplanted to create , unexpectedly found that high hematocrit (34% or higher) in the immediate postoperative period was associated with increased risk of myocardial infarction (MI) and that low hematocrit (<24%) correlated with decreased MI risk. In contrast, a multicenter, prospective study by DeFoe et al (36) examined the relationship between nadir hematocrit level and in-hospital mortality in a series of 6,980 consecutive patients undergoing isolated coronary artery bypass graft surgery Coronary Artery Bypass Graft Surgery Definition Coronary artery bypass graft surgery is a surgical procedure in which one or more blocked coronary arteries are bypassed by a blood vessel graft to restore normal blood flow to the heart. . They found a trend toward increased risk of death for patients with nadir hematocrits less than 23%. Patients with hematocrits less than l9% had mortality rates twice as high as those with hematocrits greater than or equal to 25%. Several other studies have also noted a trend toward increased mortality in cardiac patients with hemoglobin levels less than 9 to 9.5 g/dl. (37,38) A large retrospective review of data on 78,974 Medicare patients hospitalized for acute myocardial infarction acute myocardial infarction (  ·kyōōtˑ mī·ō·karˑ·dē· found that transfusion at
hematocrit levels below 30%, and possibly even 33%, was associated with
decreased odds ratio of death in the 30 days after admission. (39)
Furthermore, transfusion when the patient's hematocrit was 30% or
below was associated with improved survival probabili ty.
Critically III Patients None of the studies described above were randomized, controlled trials. Indeed, except for a pilot study from the Transfusion Requirements in Critical Care (TRICC) trial, (40) the only randomized, controlled studies published before 1999 that compared restrictive versus liberal transfusion practice in the general population (not in patients with sickle cell anemia sickle cell anemia n. A chronic, usually fatal inherited form of anemia marked by crescent-shaped red blood cells, occurring almost exclusively in Blacks, and characterized by fever, leg ulcers, jaundice, and episodic pain in the joints. ) involved 50 or fewer patients. None had sufficient power to permit definitive inferences regarding the effect of transfusion on morbidity and mortality. (41-44) The TRICC trial was the first and, to date, only large-scale, prospective, randomized, controlled clinical trial controlled clinical trial, n a research strategy that calls for two samples: an experimental sample of patients receiving a pharmaceutical, and a second sample of control patients receiving a placebo. to compare the impact of restrictive versus liberal transfusion regimens on morbidity and mortality. Conducted in randomized critical care patients, this study found that restrictive transfusion (maintaining hemoglobin between 7 and 9 g/dl) did not have an adverse effect on either 30-day survival or organ failure when compared with a liberal regimen with n hemoglobin target of 10 to 12 g/dl. Indeed, there was a trend toward lower mortality and lower multiple organ dysfunction score in the restrictive group overall, although the trend was not statistically significant. Also, in younger patients and in less severely ill patients, mortality and multiple organ dysfunction score were significantly lower in the restrictive-strategy group. (45) A recently published subset analysis of 357 patients with cardiovascular disease in the TRICC trial addressed the issue raised by Hebert et a1 (38) regarding whether transfusion does, in fact, decrease mortality in anemic critical care patients with cardiac disease. Unlike the earlier study, this subset analysis found no increase in mortality, no significant increase in complication rates (including new MI), and no difference in the degree of multiorgan dysfunction in the restrictive group, even among patients with known coronary artery disease. (46) Conclusions Although the TRICC trial seems to have resolved the issue, the observations of Wu et al raise important questions. Although the study by Wu et al was retrospective, the number of patients studied makes it impossible to ignore the findings. This is especially true given the canine data with experimental coronary stenosis and the earlier studies of Hebert and DeFoe. Indeed, in both the original article and in the subset analysis, the authors of the TRIOC trial reports themselves evidence some unease about applying these results to patients with unstable angina and myocardial infarction. Also, the uncertainty among researchers is reflected in the wide variability of clinical practice with respect to transfusion thresholds in elderly patients and in patients at risk for cardiac disease. The variety of situations in which red cell transfusions are given (or considered) makes definition of a single transfusion threshold impossible and attempts to explore the subject daunting daunt tr.v. daunt·ed, daunt·ing, daunts To abate the courage of; discourage. See Synonyms at dismay. [Middle English daunten, from Old French danter, from Latin . Rationally, one might expect, though, that the patients for whom oxygen availability in the blood is most critical--that is, those with atherosclerotic disease whose vessels are least able to dilate dilate /di·late/ (di´lat) to stretch an opening or hollow structure beyond its normal dimensions. di·late v. To make or become wider or larger. to increase blood flow when oxygen content falls--should provide the best and most broadly applicable indication of when anemia may cause morbidity. Clearly, what is most needed at this juncture is a large-scale, randomized, controlled clinical trial designed specifically to examine the population most at risk from atherosclerosis--patients with known ischemic cardiac disease. Data from such a study, coupled with the data presented here, should permit definition of safe thresholds that can be applied to the general adult population with more uniform adherence than is seen today. Accepted November 20, 2002. References (1.) Welch HG, Meehan KR, Goodnough LT. Prudent strategies for elective red blood cell red blood cell: see blood. transfusion. Ann Intern Med 1992;116:393-402. (2.) Audet AM, Goodnough LT. Practice strategies for elective red blood cell transfusion. Ann Intern Med 1992;116:404-406. (3.) Stehling L, Luban NL, Anderson KC, Sayers MH, Long A, Attar 5, et al. Guidelines for blood utilization review. Transfusion 1994;34:438-448. (4.) Becker J, Evans C; American Association of Blood Banks. Guidelines for Blood Utilization Review. Bethesda, MD, American Association of Blood Banks Press, 2001, pp 13-14. (5.) American Society of Anesthesiologists The American Society of Anesthesiologists (ASA) is an association of physicians (primarily anesthesiologists) whose stated goal is to raise and maintain the standards of the medical practice of anesthesiology and improve the care of the patient. 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The necessary and unnecessary transfusion: A critical review or reported appropriateness rates and criteria for red cell transfusions. Transfusion 1994;34:l10-115. (8.) Chiavetta JA, Herst R, Freedman J, Axcell TJ, Wall AJ, van Rooy SC. A survey of red cell use in 45 hospitals in central Ontario, Canada. Transfusion 1996;36:699-706. (9.) Hebert PC, Wells G, Martin C, Tweeddale M, Marshall J, Blajchman M, et al. A Canadian survey of transfusion practices in critically ill patients: Transfusion Requirements in Critical Care Investigators and the Canadian Critical Care Trials Group. Crit Care Med 1998;26:482-487. (10.) Blajchman MA. Immunomodulatory effects of allogeneic allogeneic /al·lo·ge·ne·ic/ (-je-ne´ik) 1. having cell types that are antigenically distinct. 2. in transplantation biology, denoting individuals (or tissues) that are of the same species but antigenically blood transfusions: Clinical manifestations and mechanisms. Vox Sang 1998; 74(Suppl 2):315-319. (11.) Kao KJ. Mechanisms and new approaches for the allogeneic blood-transfusion induced immunomodulatory effects. Transfus Med Rev 2000; 14:12-22. (12.) Langenfield JE, Livingston DH, Machiedo GW. Red cell deformability deformability /de·form·a·bil·i·ty/ (de-form?ah-bil´it-e) ability of cells to change shape when passing through narrow spaces, such as erythrocytes passing through the microvasculature. is an early indicator of infection. Surgery 1991;110:398-404. (13.) Schumacker PT, Guth B, Suggett Al, Wagner PD, West JB. Effects of transfusion-induced polycythemia polycythemia (pŏl'ēsīthē`mēə), condition characterized by an increase in the production of red blood cells, or erythrocytes, in the blood. on 02 transport during exercise in the dog. J Appl Physiol 1985;55:749-758. (14.) Julien M, Hakim TS, Vahi R, Chang HK. Effect of hematocrit on vascular pressure profile in dog lungs. J Appl Physiol 1985;58:743-748. (15.) Levine E, Rosen A, Sehgal L, Gould S, Sehgal H, Moss G. Physiologic effects of acute anemia: Implications for a reduced transfusion trigger. Transfusion 1990;30:11-14. (16.) Wilkerson DK, Rosen AL, Sehgal LR, Gould SA, Sehgal HL, Moss GS. Limits of cardiac compensation in anemic baboons. Surgery 1988;103: 665-670. (17.) Geha AS. Coronary and cardiovascular dynamics and oxygen availability during acute normovolemic anemia. Surgery 1976;80:47-53. (18.) Wright CJ. The effects of severe progressive hemodilution on regional blood flow and oxygen consumption. Surgery 1976;79:299-305. (19.) Brazier J, Cooper N, Maloney JV Jr, Buckberg G. The adequacy of myocardial myocardial /myo·car·di·al/ (-kahr´de-al) pertaining to the muscular tissue of the heart. myocardial pertaining to the muscular tissue of the heart (the myocardium). oxygen delivery in acute normovolemic anemia, Surgery 1974;75:508-516. (20.) Geha AS, Baue AE. Graded coronary stenosis and coronary flow during acute normovolemic anemia. World J Surg 1975;2:645-652. (21.) Anderson HT, Kessinger JM, McFarland W J Jr, Laks H, Geha AS. The response of hypertrophied hy·per·tro·phy n. pl. hy·per·tro·phies A nontumorous enlargement of an organ or a tissue as a result of an increase in the size rather than the number of constituent cells: muscle hypertrophy. heart to acute anemia and coronary stenosis. Surgery 1978;84:8-15. (22.) Spahn DR, Smith LR, Veronee CD, McRae RL, Hu WC, Menius AJ, et al. Acute isovolemic hemodilution and blood transfusion: Effects on regional function and metabolism in myocardium myocardium /myo·car·di·um/ (-kahr´de-um) the middle and thickest layer of the heart wall, composed of cardiac muscle. hibernating myocardium see myocardial hibernation, under with compromised coronary blood flow. J Thorac Cardiovasc Surg 1993;105:694-704. (23.) Weiskopf RB, Viele MK, Feiner J, Kelley S, Lieberman J, Noorani M, et al. Human cardiovascular and metabolic response to acute, severe isovolemic anemia. JAMA JAMA abbr. Journal of the American Medical Association 1998;279:217-221. (24.) Weiskopf RB, Kramer JH, Viele M, Neumann M, Feiner JR, Watson II, et al. Acute severe isovolemic anemia impairs cognitive function and memory in humans. Anesthesiology 2000;92: 1646-1652. (25.) Carson JL, Poses RM, Spence RK, Bonavita G.. Severe anaemia anaemia see anemia. and operative mortality and morbidity. Lancer 1988;1:727-729. (26.) Carson JL, Duff A, Poses RM, Berlin IA, Spence RK, Trout R, et al. Effect of anaemia and cardiovascular disease on surgical morbidity and mortality. Lancet 1996;348:1055-1060. (27.) Viele MK, Weiskopf RB. What can we learn about the need for transfusion from patients who refuse blood? The experience in Jehovah's Witnesses, Transfusion 1994;34:396-401. (28.) Botero C, Smith CE, Morseher AH. 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On November 2 2006, the majority of the guild members were indefinitely banned from the game for use of (or directly benefiting from) a third-party "wall-hack", used to bypass content ? Surgical outcome of Jehovah's Witnesses, Am J Med 1993;94:117-119. (33.) Nelson CL, Bowen WS. Total hip arthroplasty total hip arthroplasty, n total hip replacement; surgical reconstruction of the hip in which the ball-and-socket joint is replaced with a prosthesis. in Jehovah's Witnesses without blood transfusion. J Bone Joint Surg Am 1986;68;350-353. (34.) Carson JL, Duff A, Berlin JA, Lawrence VA, Poses RM, Huber EC, et al. Perioperative blood transfusion and postoperative mortality. JAMA 1998;279: 199-205. (35.) Spiess BD, Ley C, Body SC, Siegel LC, Stover EP, Maddi R, et al. Hematocrit value on intensive care unit entry influences the frequency of Q-wave myocardial infarction after coronary artery bypass grafting: The Institutions of the Multicenter Study of Perioperative Ischemia (McSPI) Research Group. J Thorac Cardiovase Surg 1998;116:460-467. (36.) DeFoe GR, Ross CS, Olmstead EM, Surgenor SD, Fillinger MP, Groom RC, et al. Lowest hematocrit on bypass and adverse outcomes associated with coronary artery bypass grafting: Northern New England Cardiovascular Disease Study Group. Ann Thorac Surg 2001;71:769-776. (37.) Nelson AH, Fleisher LA, Rosenbaum SH. Relationship between postoperative anemia and cardiac morbidity in high risk vascular patients in the intensive care unit. Crit Care Med 1993;21:860-866. (38.) Hebert PC, Wells G, Tweeddale M, Martin C, Marshall J, Pham B, et al. Does transfusion practice affect mortality in critically ill patients? Transfusion Requirements in Critical Care (TRICC) Investigators and the Canadian Critical Care Trials Group. Am J Respir Crit Care Med 1997;155:1618-1623. (39.) Wu WC, Rathore SS, Wang Y, Radford MJ, Krumholz HM. Blood transfusion in elderly patients with acute myocardial infarction. N Engl J Med 2001;345:1230-1236. (40.) Hebert PC, Wells G, Marshall J, Martin C, Tweeddale M, Pagliarello G, et al. Transfusion requirements in critical care: A pilot study--Canadian Critical Care Trials Group. JAMA 1995;273:1439-1444. (41.) Johnson RG, Thurer RL, Kruskall MS, Sirois C, Gervino EV, Critchlow J, et al. Comparison of two transfusion strategies after elective operations for myocardial revascularization. J Thorac Cardiovasc Surg 1992;104:307-314. (42.) Weisel RD, Charlesworth DC, Mickleborough LL, Fremes SE, Ivanov J, Mickle DA, et al. Limitations of blood conservation. J Thorac Cardiavasc Surg 1984;88:26-38. (43.) Fortune JB, Feustel PJ, Saifi J, Stratton HH, Newell JC, Shah DM. Influence of hematocrit on cardiopulmonary function after acute hemorrhage. J Trauma 1987;27:243-249. (44.) Blair SD, Janvrin SB, McCollum CN, Greenhalgh RM. Effect of early blood transfusion on gastrointestinal haemorrhage. Br J Surg 1986;73:783-785. (45.) Hebert PC, Wells G, Blajchman MA, Marshall J, Martin C, Pagliarello G, et al. A multicenter, randomized, controlled clinical trial of transfusion requirements in critical care: Transfusion Requirements in Critical Care Investigators, Canadian Critical Care Trials Group. N Engl J Med 1999;340:409-417. (46.) Hebert PC, Yetisir E, Martin C, Blajchman MA, Wells G, Marshall J, et al; Transfusion Requirements in Critical Care Investigators for the Canadian Critical Care Trials Group, Is a low transfusion threshold safe in critically ill patients with cardiovascular diseases? Crif Care Med 2001;29:227-234. RELATED ARTICLE: Key Points * Animal data and studies in human volunteers and patients support a red cell transfusion threshold of 7 to 8 g/dl in most patients. * Conflicting data, particularly in cardiac patients and in the elderly, suggest that it may be impossible to define a single red cell "trigger" for all patients. * A well-designed, randomized, controlled trial is still needed to establish a safe threshold for red cell transfusion in adults with coronary artery disease. From the Department of Pathology, UMass Memorial Medical Center, Worcester, MA. Reprint requests to Marian Petrides, MD, Blood Bank, UMass Memorial Medical Center, 55 Lake Avenue N., Worcester, MA 01655. Email: petridem@ummhc.org Copyright [C] 2003 by The Southern Medical Association 00038-4348/03/9607-0664 |
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