Anaemia Overview
Last updated 5th March 2018 - Tom Heaton
Anaemia is a common medical condition.
It has several implications for both general health and perioperative practice.
Anaemia is defined as a haemoglobin (Hb) value below the normal range.
The range of normal will vary slightly depending on the patient circumstances:
In neonates, the normal Hb is higher (15-20 g/dl) due to placental transfusion.
In pregnancy, there is a recognised dilution such that from the second trimester a lower threshold of 11g/dl is used.
Of note, there is ongoing reassessment of whether different values for men and women is actually a true representation of an appropriate baseline in health. As such, consideration of a normal lower value of 13g/dl in both sexes seems optimal.
This is a very basic explanation of anaemia from KhanAcademy (for people very new to the topic):
https://www.youtube.com/watch?v=Ty6TfxCYPQI
This is a slightly more detailed video from KhanAcademy on the pathophysiology of anaemia:
https://www.youtube.com/watch?v=LtlodYLm8fc
An overview of the pathways for haematopoiesis, including haemoglobin production, is very useful for understanding the pathology and is discussed elsewhere.
It has several implications for both general health and perioperative practice.
Anaemia is defined as a haemoglobin (Hb) value below the normal range.
The range of normal will vary slightly depending on the patient circumstances:
- Female - 12-15 g/dl
- Male - 13-16 g/d
In neonates, the normal Hb is higher (15-20 g/dl) due to placental transfusion.
In pregnancy, there is a recognised dilution such that from the second trimester a lower threshold of 11g/dl is used.
Of note, there is ongoing reassessment of whether different values for men and women is actually a true representation of an appropriate baseline in health. As such, consideration of a normal lower value of 13g/dl in both sexes seems optimal.
This is a very basic explanation of anaemia from KhanAcademy (for people very new to the topic):
https://www.youtube.com/watch?v=Ty6TfxCYPQI
This is a slightly more detailed video from KhanAcademy on the pathophysiology of anaemia:
https://www.youtube.com/watch?v=LtlodYLm8fc
An overview of the pathways for haematopoiesis, including haemoglobin production, is very useful for understanding the pathology and is discussed elsewhere.
Aetiology
There are a wide range of causes of anaemia.
This video from KhanAcademy provides a useful introduction to how we could think about the aetiology:
https://www.youtube.com/watch?v=3AMENlm4pOw&t=7s
A common method of classification is based on the RBC size.
Macrocytic
Another way of classification, and perhaps more useful for understanding the pathophysiology is based on the cause of the anaemia:
1. Reduced Production:
2. Increased destruction (haemolysis):
3. Dilution of Hb
4. Acute blood loss
The reticulocyte count can be useful to help differentiate between destruction and production causes.
A high reticulocyte count (e.g. >3%) suggests an increased production of RBC to try and respond to increased destruction.
A low reticulocyte count suggests that the haematopoietic system isn’t responding appropriately to the anaemia, and therefore the problem may lie in the production process.
This video from KhanAcademy provides a useful introduction to how we could think about the aetiology:
https://www.youtube.com/watch?v=3AMENlm4pOw&t=7s
A common method of classification is based on the RBC size.
Macrocytic
- Megaloblastic
- B12 deficiency
- Folate deficiency
- Alcoholism
- Iron deficiency anaemia
- Anaemia of chronic disease
- Reduced globin chain production
- Acute blood loss
- Haemolysis
- Anaemia of chronic disease
- Bone marrow failure
- Most non haematinic causes
Another way of classification, and perhaps more useful for understanding the pathophysiology is based on the cause of the anaemia:
1. Reduced Production:
- Substrate deficiency
- Iron
- Dietary deficiency
- Impaired utilisation
- B12
- Folate
- Copper
- Iron
- Aplastic anaemia
- Bone marrow infiltration
- Chronic kidney disease
- Endocrine failure e.g. thyroid
2. Increased destruction (haemolysis):
- Extrinsic Causes
- Excess reticuloendothelial activity
- Splenomegaly
- Immunological haemolysis
- Warm antibody haemolysis
- Cold antibody haemolysis
- Mechanical injury
- Excess reticuloendothelial activity
- Intrinsic RBC defects
- Membrane abnormalities
- Congenital erythropoietic porphyria
- Hereditary spherocytosis
- Metabolic abnormalities
- G6PD deficiency
- Haemoglobinopathies
- Sickle cell anaemia
- Thalassaemia
- Membrane abnormalities
3. Dilution of Hb
- Pregnancy
- IV fluid
4. Acute blood loss
- Trauma
- Sampling e.g. in critical care
The reticulocyte count can be useful to help differentiate between destruction and production causes.
A high reticulocyte count (e.g. >3%) suggests an increased production of RBC to try and respond to increased destruction.
A low reticulocyte count suggests that the haematopoietic system isn’t responding appropriately to the anaemia, and therefore the problem may lie in the production process.
Presentation
Anaemia can commonly be discovered incidentally on routine FBC.
When more severe, the condition can present due to a result of an imbalance between tissue oxygen demand and delivery.
Symptoms may include:
Young fit patients may just experience generalised symptoms of malaise.
Patients with additional comorbidities may have these exacerbated e.g. angina
When more severe, the condition can present due to a result of an imbalance between tissue oxygen demand and delivery.
Symptoms may include:
- Dizziness
- Shortness of breath
- Lethargy/fatigue
- Malaise
- Palpitations
- Angina
Young fit patients may just experience generalised symptoms of malaise.
Patients with additional comorbidities may have these exacerbated e.g. angina
Assessment
Anaemia is a manifestation of an underlying disease rather than a diagnosis in itself, so the assessment and investigative process should bear this in mind.
History
Risk factors for specific causes of anaemia should be sought:
Examination
In acute blood loss, this will be more an assessment of cardiovascular stability and assessment for source of bleeding.
Chronically is may provide information as to the aetiology of the anaemia:
History
Risk factors for specific causes of anaemia should be sought:
- Dietary disturbance - elective e.g. veganism, or pathological e.g. GI surgery
- Chronic inflammatory disease
- Cancer
- Alcohol misuse
- Chronic blood loss e.g. menorrhagia.
- Family history e.g. of Sickle cell
- Pregnancy
Examination
In acute blood loss, this will be more an assessment of cardiovascular stability and assessment for source of bleeding.
Chronically is may provide information as to the aetiology of the anaemia:
- Pallor - poor sensitivity unless severe anaemia
- Jaundice - from haemolysis
- Splenomegaly
- Bowel mass - abdominal or on DRE
- Petechiae - suggesting concomitant platelet abnormality
- Peripheral neuropathy - in B12 deficiency
- Heart murmur - in endocarditis
- Nail abnormalities - in substrate deficiency
Investigation
There are a number of other important parameters on a blood film that are relevant.
There are also a number of other visual finding on a blood film that provide information on the aetiology of any anaemia (though some relate to specific abnormalities of the above parameters)
Other values of a full blood count can be useful in guiding the diagnosis.
Abnormalities of platelets or white blood cells may be present.
Additional tests can provide further information on the cause of anaemia
Bone marrow biopsy may be required if the cause is felt to relate to failure of the bone marrow to produce new cells e.g. through infiltration.
Imaging may form a core part of investigation:
- Red cell count
- Male - 4.4-5.8 x 10^12/l
- Female - 4.0-5.2 x 10^12/l
- Male - 4.4-5.8 x 10^12/l
- Haematocrit
- Male - 40-51%
- Female - 38-48%
- Male - 40-51%
- Mean cell volume - 76-96 fl
- Mean cell haemoglobin - 27-32 pg
- Mean cell haemoglobin concentration - 32-36 g/dl
- Reticulocyte count - 1-2%
There are also a number of other visual finding on a blood film that provide information on the aetiology of any anaemia (though some relate to specific abnormalities of the above parameters)
- Hypochromia - pale RBCs due to low Hb concentrations
- Anisocytosis - the size of the RBCs is variable
- Poikilocytosis - the shape of the RBCs is irregular and variable
- Macrocytic - RBCs are generally larger in size
- Microcytic - RBCs are generally smaller in size
- Reticulocytosis - an increase in immature RBCs, seen in acute blood loss.
Other values of a full blood count can be useful in guiding the diagnosis.
Abnormalities of platelets or white blood cells may be present.
Additional tests can provide further information on the cause of anaemia
- Haematinics
- B12
- Folate
- Serum iron
- Ferritin
- Total iron binding capacity
- B12
- Coombs test - identifies antibodies
- Haptoglobin
- Electrophoresis
Bone marrow biopsy may be required if the cause is felt to relate to failure of the bone marrow to produce new cells e.g. through infiltration.
Imaging may form a core part of investigation:
- Endoscopy - to look for malignancy of the GI tract
- Radiology - to look for malignancy. To assess for splenomegaly.
Perioperative Management
Perioperative anaemia is a common disturbance and can be associated with a notable increase in the risk of morbidity and mortality.
As such, there has been a strong focus to minimise the impact of anaemia on the patient, particularly relating to minimising the need for blood transfusion.
The Patient Blood Management (PBM) approach is a good example of this. This focuses on the 3 pillars of:
Detection and management needs to be built into pre-op pathways, with a major focus on identifying reversible causes of anaemia, especially iron deficiency.
This is explored in more detail in the section on iron deficiency anaemia.
Early detection is probably the key to enabling appropriate next steps to be taken, as there is often a range of options available to improve the anaemia.
Intraoperative care has a particular focus on minimising blood loss and optimising the physiology of the patient, especially coagulation. This includes:
This links into a focus on minimising the need for blood transfusion.
A restrictive transfusion threshold (70g/L) is now well recognised as being appropriate in the vast majority of patients.
A higher threshold of 80g/L is appropriate in those with acute coronary syndrome.
Transfusion should be done on a single unit basis with rechecking, unless there is active bleeding.
As such, there has been a strong focus to minimise the impact of anaemia on the patient, particularly relating to minimising the need for blood transfusion.
The Patient Blood Management (PBM) approach is a good example of this. This focuses on the 3 pillars of:
- Detection and management of anaemia
- Minimisation of blood loss and optimisation of coagulation
- Optimising patient physiological tolerance of anaemia.
Detection and management needs to be built into pre-op pathways, with a major focus on identifying reversible causes of anaemia, especially iron deficiency.
This is explored in more detail in the section on iron deficiency anaemia.
Early detection is probably the key to enabling appropriate next steps to be taken, as there is often a range of options available to improve the anaemia.
Intraoperative care has a particular focus on minimising blood loss and optimising the physiology of the patient, especially coagulation. This includes:
- Use of tranexamic acid
- Minimising haemodilution from excess IV fluid
- Surgical techniques to minimise blood loss e.g. tourniquets, minimally invasive surgery
- Optimising physiology for haemostasis
This links into a focus on minimising the need for blood transfusion.
A restrictive transfusion threshold (70g/L) is now well recognised as being appropriate in the vast majority of patients.
A higher threshold of 80g/L is appropriate in those with acute coronary syndrome.
Transfusion should be done on a single unit basis with rechecking, unless there is active bleeding.
Links & References
- Dimech, J. Anaemia. e-LFH. 2012
- Tidy, C. Peripheral blood films. Patient.info. 2016. https://patient.info/doctor/peripheral-blood-film
- KhanAcademy. www.khanacademy.org
- Beers, M et al (eds). The Merck Manual (18th ed). 2006. Merck Research Laboratories.
