Check this; a patient is in your ICU or ED who is hemodynamically stable, but is experiencing some tachycardia (124 bpm). They complain of dark tarry stools for the last two days. So naturally you tell the practitioner who is on that you want to check a CBC STAT on this patient. The lab is working at lightspeed today and you get your patient’s CBC in record time; the hgb is 6.4. You tell the provider that you think the patient needs a unit of blood, and you are right with your clinical judgement. But here is the next question: Why is < 7.0 g/dL appropriate for transfusion?
For quite some time there was always the understanding of the “10/30” rule. For years this rule stood as the gold standard, to transfuse if hemoglobin under 10 g/dL and/or hematocrit under 30 percent. This practice started to be questioned during the 1980’s when a concern arises regarding transfusion reactions and blood-borne pathogens.
What is the importance of hemoglobin in the body
In the body, red blood cells (RBC’s) are what delivers oxygen to the tissues. A component of that whole blood is a metalloprotein called hemoglobin. Hemoglobin carries the majority of oxygen to the tissues and end organs. In examining this further, a patient who becomes anemic or has a decrease in hemoglobin that is measured, indicates that there is a reduction in oxygen delivery to tissues.
Delivery of oxygen (DO2) = Cardiac output (CO) x arterial oxygen
The body in all of its wonderful aspects will compensate for the fall in blood levels by increasing cardiac output (as long as that is not impaired) in order to increase oxygen delivery and extraction at the site of the tissues. The question that we have to ask is; What severity of anemia can the body tolerate without impacting oxygen delivery to tissues?
In the past, as stated before, practitioners justified the transfusion principle of a hemoglobin of 10 g/dL or higher. However, large multicenter trials are starting to show that hemoglobin levels of 7-8 g/dL are adequate and associated with equivocal and sometimes even better outcomes due to risks of transfusions.
Complications of transfusions
- Infections: Viruses, bacteria and parasites that were present in the donor’s blood can escape the detection screening.
- Volume overload: Mainly concerned in elderly, pediatrics and those with reduced cardiac function.
- This leads to what is considered transfusion-associated circulatory overload (TACO) and transfusion-related acute lung injury (TRALI). These occur within six hours of blood transfusions.
- TRALI is the leading cause of mortality associated with transfusions in the United States (US). The mortality of this disease is 5-10% which equates to 200-400 deaths in the US per year because of TRALI.
- During massive transfusion of packed red blood cells electrolyte derangements can be noted. These imbalances include hyperkalemia and hypocalcemia. Hypocalcemia occurs as a result of citrate that is used during storage to help the blood from coagulating.
- So if the team has activated massive transfusion protocol, as the bedside warrior it is okay to suggest an evaluation of electrolytes or even administration of prophylactic calcium.
What should we transfuse for?
In this study by Carson et al. in 2002, retrospective data was reviewed looking at patients who refused blood products (due to religious beliefs) and evaluated their outcomes related to their hgb levels. They found that the adult population with hgb levels 7.1 to 8.0 g/dL had a lower mortality rate than those whose hgb was lower. A hgb of 5.1-7.0 showed a mortality of 9.2%, 3.1-5.0 showed 26.7% mortality and </= 3.0 showed 62.1% mortality within 30 days.
In 2014, a study was completed to follow up on these initial findings. This cohort confirmed that hgb levels 7-8 g/dL carried a lower mortality risk than in those patients with a lower anemia.
Why not transfuse higher than 7-8 g/dL?
Well I am glad that you asked! In 2016 Carson completed a large review of randomized control trials to evaluate liberal (8-9 g/dL) versus strict transfusion targets (7-8 g/dL). This study had two groups, transfusion between 7-8 g/dL and a second ground between 8-9 g/dL. There was no evidence that showed a significant difference in mortality within 30 days. However, those who were in the 7-8 g/dL group showed that there was a reduction in 43% of patients who were exposed to blood transfusions.
The exception for transfusion goal > 8
Those who experience pre-existing or current active cardiac disease, orthopedic surgery or cardiac surgery have been initially shown to have higher risk and mortality with more restricted transfusion goals. However, two landmark studies, the TRICC and FOCUS trials showed that a liberal transfusion strategy did not improve mortality in those with high cardiovascular risk.
The American Association of Blood Banks (AABB) have reviewed all of these trials and have come up with their recommendations. AABB states that a transfusion threshold of 8 g/dL is appropriate for orthopedic or cardiac surgery patients, as well as pre existing cardiovascular disease patients. This is a strong recommendation with moderate quality of evidence. The AABB also goes on to state that a restrictive threshold of 7 g/dL could be appropriate but there is not enough randomized control trial evidence to make this decision.
Also make sure to visit this interesting article on our site that explores alternative strategies to improving anemia.
- Know your patient’s current and past medical history to appropriately assess their transfusion threshold.
- Keep >7.0 g/dl in non-cardiac and orthopedic surgery patients.
- Those undergoing orthopedic surgery, cardiac surgery, pre-existing cardiac disease or active cardiac disease transfuse for > 8.0 g/dL.
- Know the adverse reactions to transfusions.
- Consider suggesting electrolytes for patients receiving massive transfusion.
- Carson JL, Guyatt G, Heddle NM, et al. Clinical Practice Guidelines From the AABB: Red Blood Cell Transfusion Thresholds and Storage. JAMA. 2016;316(19):2025–2035. doi:10.1001/jama.2016.9185
- Carson JL, Noveck H, Berlin JA, Gould SA. Mortality and morbidity in patients with very low postoperative Hb levels who decline blood transfusion. Transfusion. 2002;42(7):812-818. doi:10.1046/j.1537-2995.2002.00123.x
- Carson JL, Terrin ML, Noveck H, et al. Liberal or restrictive transfusion in high-risk patients after hip surgery. N Engl J Med. 2011;365(26):2453-2462. doi:10.1056/NEJMoa1012452
- Hébert PC, Wells G, Blajchman MA, 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 [published correction appears in N Engl J Med 1999 Apr 1;340(13):1056]. N Engl J Med. 1999;340(6):409-417. doi:10.1056/NEJM199902113400601
- Popovsky MA. Transfusion-Related Acute Lung Injury: Incidence, Pathogenesis and the Role of Multicomponent Apheresis in Its Prevention. Transfus Med Hemother. 2008;35(2):76-79. doi:10.1159/000117811
- Shander A, Javidroozi M, Naqvi S, et al. An update on mortality and morbidity in patients with very low postoperative hemoglobin levels who decline blood transfusion (CME). Transfusion. 2014;54(10 Pt 2):2688-2687. doi:10.1111/trf.12565