Blood transfusion

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Historical Aspects

Early Attempts

Much of the science that underpins blood transfusion is obvious in hindsight, but protracted development of blood transfusion must be viewed in the wider context of the many other discoveries that had to come first.

In was only in 1628 that William Harvey described the concept of a blood circulation. Following on from this discovery, blood transfusions were indeed attempted, but in addition to human blood, several other substances were administered including animal blood. With no concept of blood groups and therefore no matching, an estimated 1 out of 3 human transfusions would have resulted in incompatibility. The dire consequences of transfusion led to its prohibition in France and England in 1678.

The technique lay in disrepute for well over a century until 1818 when a London obstetrician named James Blundell became the first person to state clearly that humans should only receive human blood. Blundell conducted several tranfusion experiments, but equipment was crude, and without the appreciation of blood groups, fatalities were inevitable.

Even in the second half of the 19th century, this dangerous practice continued along side some even more bizarre and hazardous practices. Animal to human transfusions continued, but there were also attempts to transfuse animal milk and even human milk based on the notion that the fat particles in milk could be converted into blood cells.

Blood Groups Discovered

Saline was discovered as a viable alternative to dangerous blood transfusion, but the eventual discovery of the ABO blood groups did not happen until the beginning of the 20th century. Karl Landsteiner work on mixing blood samples from different individuals led to the description of the ABO blood groups (which earned him a belated Nobel prize in 1930).

Even after this discovery, blood transfusion took many years to become established, partly because the techniques of collecting blood and preventing it from clotting had not been fully developed. Anti-coagulation was used in World War I, but it was World War II that provided the impetus for stored blood in the form blood banks. In the post-World War II era, blood banks were set up across the United States and several other countries including the Britain. Further developments in science and technology, particularly the development of plastics greatly aided the practice of blood transfusion.

The Spectre of Blood Borne Viruses

As early as 1943, it was observed that some patients developed 'post-tranfusion hepatitis'. Increasing used of blood also saw an increase in hepatitis. Although little was known about the causative agents, blood from paid donors was associated with an increased risk of the recipient contracting hepatitis. This was not surprising as many of the paid 'professional' donors included high risk groups such as intravenous drug users. Blood transfusion was made purely voluntary and remains so in most parts of the world.

The identification of the hepatitis viruses in the 1970s and 1980s was followed by the threat of HIV. Sadly, the discovery of these viruses came too late to prevent numerous transfusion patients from becoming infected with these viruses after receiving blood from infected sources. The fact that many patients contracted incurable diseases through supposedly life-saving therapy altered the perception of a process that had previously been regarded with great wonder.

More recently, the theoretical risk that new variant Creutzfeldt-Jakob disease could be transmitted through B lymphocytes led to the UK transfusion services to source plasma from outside the UK. Additionally, since 1999, all collected UK blood is routinely leucodepleted to remove white blood cells.

Blood components

Red cells

Given as red cell concentrate or synonymously packed red cells. 1 unit raises haemoglobin by approximately 1g/dL.

Calculations based on ~450ml±10% of whole blood is added to 63ml anti-coagulant and processed to remove plasma leaving a volume of 280±60 ml with a haematocrit of approximately 50-70% and therefore a total haemoglobin of about 40-70g/unit (>40g according to standard).[1]


There is considerable controversy, but most are agreed that with the known physiology in health and disease, the potential risks of blood transfusion mean that the "10/30" rule (Hb> 10g/dl and haematocrit > 30% before operation) that formerly applied makes little sense as does a "transfusion trigger" of 10g/dl. In health humans the optimal haematocrit is about 35%[2] although flow through small vessels may be optimal at higher values with some variation with say neonates compared to adults[3].


The published evidence base is inconclusive but consistent with Hb about 8g/dl not being associated with harm.

Intensive care
  • 30-day mortality was 23% in ITU patients maintained at Hb 10-12g/l and 19% for those maintained at Hb 7-9 g/dl with a significant reduction in heart failure in the later group.[4]. Trends in this and other studies are towards better long term mortality and less myocardial infarction, as well as a 40-50% drop in tranfusion requirement in either adults or children[5] for Hb in the 7-9g/dl range.
Chronic anaemia

Fatigue, weakness dizziness and reduced exercise tolerance in the context of anaemia that do not reduce meaningful patient function do not justify transfusion. In severe anaemia in children with malaria those whose Hb was kept above 4 g/dl did much better[6]. In thalaesemma and sickle cell disease, 9-10g/dl seem optimal[7].

Cardiovascular disease

Multiple studies show inconsistent correlation with degree of anaemia down to 8 g/dl and haemocrit lower than 33% improved outcome in one large study of myocardial infarction[8].


Can be produced by:

  1. Platelet rich plasma (PPP) with >60 x109 in ≥ 75% units[9]
  2. Buffy-coat (BC) with >60 x109 in ≥ 75% units[9]
  3. Apheresis with >200 x109 in ≥ 90% units[9]


General guidance to be adjusted for individual adult patient circumstances is[10]:

  • platelet count ≤ 10,000/µl in blood dyscrasia or malignancy if patient stable
  • platelet count ≤ 20,000/µl in major haemorrhage or other high risk situations such as fever, rapidly decreasing platelet count or sepsis
  • platelet count ≤ 50,000/µl prior to major surgery
  • platelet count ≤ 100,000/µl prior to neurosurgery

Exceptions to this are likely to apply with CABG, TTP, HIT, ITP where platelet transfusion is either ineffective or dangerous and neonates where special precautions and criteria apply.

  • For dose use local guidance as no consensus but usually about 50-100 x109 platelets/10kg

Freshly Frozen Plasma


  • These might vary due to the availability of more specific blood products. Generally recombinant factor VIIa is used now in haemophilia.
  • Reversal oral anticoagulants.



These might vary due to the availability of more specific blood products. Von Willebrand's disease is usually now treated with pdFVIII products enriched with von Willebrand factor.


Because the potential for extreme harm and even death from blood transfusion exists an audit scheme via the national body called Serious Hazards of Transfusion is in place.

  • Labelling errors
  • From delivery systems
    • cannula site infection, air embolus, haematoma
  • Fluid overload
  • Transfusion reactions
    • Fever, shortness of breath, shivers, chest pain, back pain, rash
  • anaphylaxis
  • transfusion related acute lung injury (TRALI)
  • transmission of infection (estimated at 1 in 2 million transfused units in UK for HIV infection)
  • suppression of immune response
  • iron overload

External Links


  1. [ Guidelines for the Blood Transfusion Services in the UK 2007 (7th Edition).] UK Blood Transfusion Services.
  2. Crowell JW, Smith EE. Determinant of the optimal hematocrit. Journal of applied physiology. 1967 Mar; 22(3):501-4.
  3. Linderkamp O, Stadler AA, Zilow EP. Blood viscosity and optimal hematocrit in preterm and full-term neonates in 50- to 500-micrometer tubes. Pediatric research. 1992 Jul; 32(1):97-102.
  4. Hébert PC, Wells G, Blajchman MA, Marshall J, Martin C, Pagliarello G, Tweeddale M, Schweitzer I, Yetisir E. A multicenter, randomized, controlled clinical trial of transfusion requirements in critical care. Transfusion Requirements in Critical Care Investigators, Canadian Critical Care Trials Group. The New England journal of medicine. 1999 Feb 11; 340(6):409-17.
  5. Lacroix J, Hébert PC, Hutchison JS, Hume HA, Tucci M, Ducruet T, Gauvin F, Collet JP, Toledano BJ, Robillard P, Joffe A, Biarent D, Meert K, Peters MJ. Transfusion strategies for patients in pediatric intensive care units. The New England journal of medicine. 2007 Apr 19; 356(16):1609-19.(Link to article – subscription may be required.)
  6. English M, Ahmed M, Ngando C, Berkley J, Ross A. Blood transfusion for severe anaemia in children in a Kenyan hospital. Lancet. 2002 Feb 9; 359(9305):494-5.
  7. Klein HG, Spahn DR, Carson JL. Red blood cell transfusion in clinical practice. Lancet. 2007 Aug 4; 370(9585):415-26.(Link to article – subscription may be required.)
  8. Klein HG, Spahn DR, Carson JL. Red blood cell transfusion in clinical practice. Lancet. 2007 Aug 4; 370(9585):415-26.(Link to article – subscription may be required.)
  9. a b c Guide to the Preparation, Use and Quality Assurance of Blood Components, 13th ed, Strasbourg: Council of Europe Publishing: March 2007, AABB standards used in North America are different (Standards for Blood Banks and Transfusion Services, 23rd edn Bethesda, Maryland: AABB 2004)
  10. Stroncek DF, Rebulla P. Platelet transfusions. Lancet. 2007 Aug 4; 370(9585):427-38.(Link to article – subscription may be required.)