Should I order a blood transfusion based on the hemoglobin (Hgb) or the hematocrit (Hct)?

Despite the frequent interchangeability of Hgb (g/dL) and Hct (%) by a ratio of ~1:3, directly-measured blood Hgb levels may be preferred for assessing the need for blood transfusion for at least 3 reasons:

First, in contrast to the widely-used automated measurements of Hct, Hgb is not affected by conditions that affect the size of the RBCs or the mean corpuscular Hgb concentration (MCHC). This is because the Hct is not a direct measure of Hgb; rather it’s the proportion of blood occupied by RBCs which, in automated systems, is derived by multiplying the number of RBCs by the mean corpuscular volume (MCV).1-3

This may not be a significant issue when MCHC is normal, but when MCHC is abnormal, HCT may not accurately reflect the blood Hgb concentration. For example, in patients with hypochromic iron deficiency anemia with RBCs containing less hemoglobin (ie, low MCHC), the Hct may overestimate blood Hgb levels. Conversely in hereditary spherocytosis with its attendant low RBC volume and high MCHC, the Hct may underestimate Hgb levels.

Second, Hct results may also be more subject to technical factors in the lab. For example, blood at room temperature between 6-24 h may be associated with RBC swelling and increased Hct without any change in its Hgb concentration.4

Finally, national and international guidelines on blood transfusion generally target Hgb, not Hct results.5-7

For a related pearl, go to https://pearls4peers.com/2016/11/01/should-i-use-a-hemoglobin-level-of-7-or-8-gdl-as-a-threshold-for-blood-transfusion-in-my-hospitalized-patient.

 

References

  1. Tefferi A, Hanson CA, Inwards DJ. How to interpret and pursue an abnormal complete blood cell count in adults. Mayo Clin Proc 2005;80:923-36. https://www.ncbi.nlm.nih.gov/pubmed/16007898
  2. Macdougall IC, Ritz E. The Normal Haematocrit Trial in dialysis patients with cardiac disease: are we any the less confused about target hemoglobin? Nephrol Dial Transplant 1998;13:3030-33. https://academic.oup.com/ndt/article-pdf/13/12/3030/9907456/3030.pdf
  3. Kelleher BP, Wall C, O’Broin SD. Haemoglobin, not haematocrit, should be the preferred parameter. Nephrol Dial Transplant 2001;16:1085-87. https://www.ncbi.nlm.nih.gov/pubmed/11328933
  4. Hayuanta HH. Can hemoglobin-hematocrit relationship be used to assess hydration status? CDK-237/vol 43 no.2, th. 2016 http://www.kalbemed.com/Portals/6/20_237Opini-Can%20Hemoglobin-Hematocrit%20Relationship%20Be%20Used%20to%20Assess%20Hydration%20Status.pdf
  5. Blood transfusion. NICE guideline, November, 2015. https://www.nice.org.uk/guidance/ng24/chapter/Recommendations#fresh-frozen-plasma-2 uk
  6. National Blood Authority: Australia. Patient blood management, November 2016. https://www.blood.gov.au/system/files/documents/nba-patient-blood-management-resource-guide-nov_2016_v3_sm_web_file.pdf
  7. Carson JL, Guyatt G, Heddle NM, et al. Clinical practice guidelines from the AAABB: red blood cell transfusion thresholds and storage. JAMA 2016; 316:2025-2035. https://www.ncbi.nlm.nih.gov/pubmed/27732721

 

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Should I order a blood transfusion based on the hemoglobin (Hgb) or the hematocrit (Hct)?

My patient with aortic sclerosis has a loud systolic ejection murmur. What is the exact mechanism of this murmur?

We usually blame cardiac murmurs on the “turbulence” caused by blood flowing past an irregular valve surface but, believe it or not, how the murmur is created has been a matter of controversy. 1-4

For sure, murmurs are generated by disturbance of laminar blood flow (ie, turbulence) but over the years many have argued that turbulence per se fails to produce adequate acoustic force to be audible at the chest wall.2 Although challenged by some,1  the concept of “vortex shedding” borrowed from fluid dynamics is fascinating and has been proposed as a potential explanation.

Per this theory, just as a boulder causes a stream to separate and generate vortices, valves (particularly when abnormal) also create vortices. As the vortices are shed near the valve, they leave in their place relatively calm wakes which are then rapidly filled by flowing blood, creating the sound of a murmur.  

Two important variables in this theory are velocity and viscosity. When the velocity of blood flow increases substantially as in high cardiac output states (eg, fever, pregnancy), vortex shedding and the intensity of the murmur also increase. Similar phenomenon may be expected when the blood viscosity is lowered (eg, in anemia).

 

References

  1. Sabbah HN, Stein PD. Turbulent blood flow in humans: Its primary role in the production of ejection murmurs. Circ Res 1976;38: 513-24. https://www.ncbi.nlm.nih.gov/pubmed/1269101
  2. Alpert MA, Systolic murmurs. In Walker HK, Hall WD, Hurst JW. Clinical methods: The history, physical, and laboratory examinations. 3rd ed. Butterworths, Boston, 1990. https://www.ncbi.nlm.nih.gov/books/NBK345/
  3. Bruns D. A general theory of the causes of murmurs in the cardiovascular system. Am J Med 1959;27:360-74. http://www.amjmed.com/article/0002-9343(59)90002-6/fulltext
  4. Guntheroth WG. Innocent murmurs: A suspect diagnosis in non-pregnant adults. Am J Cardiol 2009;104:735-7. https://www.ncbi.nlm.nih.gov/pubmed/19699354
My patient with aortic sclerosis has a loud systolic ejection murmur. What is the exact mechanism of this murmur?

Is iron therapy contraindicated in my patient with active infection?

In the absence of randomized-controlled trials of iron therapy in patients with active infection, the harmful effects of iron therapy (IT) in this setting remains more theoretical than proven. 1,2

Although many pathogens (eg, E. coli, Klebsiella, Salmonella, Yersinia, and Staphylococcus species) depend on iron for their growth2,3, and iron overload states (eg, hemochromatosis) predispose to a variety of infections, studies evaluating the risk of infection with iron therapy have reported conflicting results.1-4 A 2015 systematic review and meta-analysis of 103 trials comparing IV iron therapy  with several other approaches, including oral iron therapy or placebo, found no increased risk of infections with IV iron.5 In contrast, an earlier systematic review and meta-analysis involving fewer number of trials found an increased risk of infections with IV iron. 6

These varied results are perhaps not surprising since the effects of iron therapy on the risk of infection is likely to be context-specific, depending on the patient’s preexisting iron status, exposure to potential infections and co-infection and genetic background. 4 Of interest, mice with sepsis have worse outcomes when treated with IV iron.7

Perhaps the most prudent approach is to hold off on iron therapy until the active infection is controlled, unless the benefits of urgent iron therapy is thought to outweigh its theoretical harmful effects.

 

References

  1. Daoud E, Nakhla E, Sharma R. Is iron therapy for anemia harmful in the setting of infection? Clev Clin J Med 2011;78:168-70. http://www.mdedge.com/ccjm/article/95480/hematology/iron-therapy-anemia-harmful-setting-infection
  2. Hain D, Braun M. IV iron: to give or to hold in the presence of infection in adults undergoing hemodialysis. Nephrology Nursing Journal 2015;42:279-83. https://www.ncbi.nlm.nih.gov/pubmed/26207288
  3. Jonker FAM, van Hensbroek MB. Anaemia, iron deficiency and susceptibility of infections. J Infect 204;69:523-27. https://www.ncbi.nlm.nih.gov/pubmed/28397964
  4. Drakesmith H, Prentice AM. Hepcidin and the iron-infection axis. Science 2012;338:768-72. https://www.ncbi.nlm.nih.gov/pubmed/23139325  
  5. Avni T, Bieber A, Grossman A, et al. The safety of intravenous iron preparations: systematic review and meta-analysis. Mayo Clin Proc 2015;90:12-23. http://www.mayoclinicproceedings.org/article/S0025-6196(14)00883-0/pdf
  6. Litton E, Xiao J, Ho KM. Safety and efficacy of intravenous iron therapy in reducing requirement for allogeneic blood transfusion: systematic review and meta-analysis of randomized clinical trials. BMJ 2013;347:f4822. https://www.ncbi.nlm.nih.gov/pubmed/23950195
  7. Javadi P, Buchman TG, Stromberg PE, et al. High dose exogenous iron following cecal ligation and puncture increases mortality rate in mice and is associated with an increase in gut epithelial and splenic apoptosis. Crit Care Med 2004;32:1178-1185. https://www.ncbi.nlm.nih.gov/pubmed/15190970
Is iron therapy contraindicated in my patient with active infection?

What is the mechanism of anemia of chronic disease in my patient with rheumatoid arthritis?

Anemia of chronic disease (ACD)—or more aptly “anemia of inflammation”— is the second most common cause of anemia after iron deficiency and is associated with numerous acute or chronic conditions (eg, infection, cancer, autoimmune diseases, chronic organ rejection, and chronic kidney disease)1.

The hallmark of ACD is disturbances in iron homeostasis which result in increased uptake and retention of iron within cells of the reticuloendothelial system, with its attendant diversion of iron from the circulation and reduced availability for erythropoiesis1. More specifically, pathogens, cancer cells, or even the body’s own immune system stimulate CD3+ T cells and macrophages to produce a variety of cytokines, (eg, interferon-ɤ, TNF-α, IL-1, IL-6, and IL-10) which in turn increase iron storage within macrophages through induction of expression of ferritin, transferrin and divalent metal transporter 1.

In addition to increased macrophage storage of iron, ACD is also associated with IL-6-induced synthesis of hepcidin, a peptide secreted by the liver that decreases iron absorption from the duodenum and its release from macrophages2. TNF-α and interferon-ɤ also contribute to ACD by inhibiting the production of erythropoietin by the kidney.  Finally, the life span of RBCs is adversely impacted in AKD due to their reduced deformability and increased adherence to the endothelium in inflammatory states3.

Of interest, it is often postulated that by limiting access to iron through inflammation, the body hinders the growth of pathogens by depriving them of this important mineral2.

 

References

  1. Weiss, G and Goodnough, L. Anemia of chronic disease. N Engl J Med 2005; 352; 1011-23. http://www.med.unc.edu/medclerk/medselect/files/anemia2.pdf
  2. D’Angelo, G. Role of hepcidin in the pathophysiology and diagnosis of anemia. Blood Res 2013; 48(1): 10-15. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3624997/pdf/br-48-10.pdf                                                                                                                                  
  3. Straat M, van Bruggen R, de Korte D, et al. Red blood cell clearance in inflammation. Transfus Med Hemother 2012;39:353-60. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3678279/pdf/tmh-0039-0353.pdf

 

Contributed by Amir Hossein Ameri, Medical Student, Harvard Medical School

                     

What is the mechanism of anemia of chronic disease in my patient with rheumatoid arthritis?

How should I interpret high serum vitamin B12 levels in my patient with anemia?

High serum B12 levels, aka hypercobalaminemia (HC),  is not rare among hospitalized patients with 1 study reporting “high” (813-1355 pg/ml) and “very high” (>1355 pg/ml) serum B12 levels in 13 and 7% of patients, respectively1.

Common causes include excess B12 intake, solid neoplasms (particularly, hepatocellular carcinoma and metastatic neoplastic liver disease), blood disorders (eg, myelodysplastic syndrome, CML, and acute leukemias, particularly AML3), and other liver diseases, including alcohol-related diseases as well as acute and chronic hepatitis.  Other inflammatory states and renal failure have also been reported2.  

Paradoxically, even in the presence of HC, a functional B12 deficiency may still exist. This may be related to poor B12 delivery to cells due to its high binding by transport proteins transcobalamin I and III in HC which may in turn cause a decrease in the binding of B12 to transcobalamin II, a key player in B12 transport to tissues2.  In this setting, elevated serum methylmalonic acid and homocysteine levels may be helpful.

References:

  1. Arendt JFB, Nexo E. Cobalamin related parameters and disease patterns in patients with increased serum cobalamin levels. PLoS ONE 2012;9:e45979. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0045979
  2. Andres E, Serraj K, Zhu J. et al. The pathophysiology of elevated vitamin B12 in clinical practice. Q J Med 2013;106:505-515.https://www.ncbi.nlm.nih.gov/pubmed/23447660
How should I interpret high serum vitamin B12 levels in my patient with anemia?

Should I use a hemoglobin level of 7 or 8 g/dL as a threshold for blood transfusion in my hospitalized patient?

Unlike its previous 2012 guidelines that recommended overlapping hemoglobin level triggers of 7 g/dL to 8 g/dL for most inpatients, the 2016 guidelines from AABB (formerly known as the American Association of Blood Banks) assigns 2 distinct tiers of hemoglobin transfusion triggers: 7 g/DL for hemodynamically stable adults, including those in intensive care units, and 8 g/dL for patients undergoing cardiac or orthopedic surgery or with preexisting cardiovascular disease1 , often defined as history of coronary artery disease, angina, myocardial infarction, stroke, congestive heart failure, or peripheral vascular disease2,3.  

These recommendations are based on an analysis of over 30 randomized trials, taking into account the potential risks of withholding transfusions, including 30-day mortality, and myocardial infarction. The new 2-tier recommendation specifically excludes those with acute coronary syndrome, severe thrombocytopenia (patients treated for hematological or oncological reasons who are at risk of bleeding), and chronic transfusion-dependent anemia.

The guidelines also emphasize that good clinical practice dictates considering not only the hemoglobin level but the overall clinical context when considering blood transfusion in patients. These factors include alternative therapies to transfusion, rate of decline in hemoglobin level, intravascular volume status, dyspnea, exercise tolerance, light-headedness, chest pain considered of cardiac origin, hypotension, tachycardia unresponsive to fluid challenge, and patient preferences.

References

  1. Carson JL, Guyatt G, Heddle NW. Clinical practice guidelines from the AABB red blood cell transfusion thresholds and storage. JAMA. Doi:10.1001/jama.2016.9185. Published online October 12, 2016. https://www.ncbi.nlm.nih.gov/pubmed/27732721
  2. Carson JL, Duff A, Poses RM, et al. Effect of anemia and cardiovascular disease on surgical mortality and morbidity. Lancet 1996;348:1055-60. https://www.ncbi.nlm.nih.gov/pubmed/8874456
  3. Carson JL, Siever F, Cook DR, et al. Liberal versus restrictive blood transfusion strategy: 3-year survial and cause of death results from the FOCUS randomized controlled trial. Lancet 2015;385:1183-1189. https://www.ncbi.nlm.nih.gov/pubmed/25499165
Should I use a hemoglobin level of 7 or 8 g/dL as a threshold for blood transfusion in my hospitalized patient?

My elderly patient with aortic stenosis has iron deficiency in the setting of Heyde’s syndrome. Can surgical or transcatheter aortic valve replacement (SAVR, TAVR) reduce her risk of future gastrointestinal bleeding?

Yes! Heyde’s syndrome, characterized by aortic stenosis and GI angiodysplasia1, appears to respond to SAVR or TAVR by reducing future risk of GI bleed.

Cessation of bleeding following SAVR or TAVR with gradual disappearance of angiodysplasia has been reported, in some cases despite long-term anticoagulant therapy2,3In fact, GI bleed may cease in 95% of cases following AVR vs 5% in cases controlled with laparotomy with or without bowel resection.  Further supporting the potential role of valve replacement is the observation that in patients who have undergone SAVR, aortic valve restenosis usually leads to the recurrence of GI bleeding which again resolves after redo surgery.

The pathophysiology of Heyde’s syndrome involves not only increased number of angiodysplasias but higher risk of bleeding from them.  Although its exact  physiological link is unclear, hypo-oxygenation of intestinal mucosa—possibly related to cholesterol emboli with resultant vasodilatation—has been hypothesized, among many others.4   Bleeding from angiodysplasias appears related to the high shear stress across the stenotic aortic valve, leading to acquired von Willebrand’s disease (Type 2AvWF disease) and coagulopathy.4

 

References

    1. Heyde EC. Gastrointestinal bleeding in aortic stenosis. N Engl J Med 1958;259:196. https://www.nejm.org/doi/full/10.1056/NEJM200209123471122
    2. Abi-akar R, El-rassi I, Karam N et al. Treatment of Heyde’s syndrome by aortic valve replacement. Curr Cardiol Rev 2011;  7:47–49. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3131716/
    3. Pyxaras, SA, Santangelo S. Perkan A et al. Reversal of angiodysplasia-derived anemia after transcatheter aortic valve implantation. J Cardiol Cases 2012; 5: e128–e131. https://www.sciencedirect.com/science/article/pii/S187854091100079X
    4. Kapila A, Chhabra L, Khanna A. Valvular aortic stenosis causing angiodysplasia and acquired von Willebrand’s disease: Heyde’s syndrome. BMJ Case Rep 2014 doi:10.1136/bcr-2013-201890. http://casereports.bmj.com/content/2014/bcr-2013-201890.full.pdf

 

Contributed by Biqi Zhang, Medical Student,  Harvard Medical School

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My elderly patient with aortic stenosis has iron deficiency in the setting of Heyde’s syndrome. Can surgical or transcatheter aortic valve replacement (SAVR, TAVR) reduce her risk of future gastrointestinal bleeding?