ANAEMIA
Definition
Anaemia is characterised by a reduction in either the hematocrit (red blood cell [RBC] volume <42% in men and <36% in women) or the concentration of haemoglobin (<130 g/L in men and <115 g/L in women). The prevalence of anaemia is highest among menstruating women (5.8%), infants (5.7%), and the elderly (12%). Anaemias can be distinguished morphologically based on the size of the RBCs or the mean corpuscular volume.
Microcytic anaemias are characterised by small RBCs (mean corpuscular volume <80 fL) and include iron-deficiency anaemia, anaemia of chronic disease, thalassaemias, and sideroblastic anaemias.
Macrocytic anaemias are characterised by large RBCs (mean corpuscular volume >98 fL) and include megaloblastic anaemias (e.g., due to vitamin B12 [pernicious anaemia] and folic acid deficiencies), myelodysplastic anaemias (e.g., from cancer chemotherapy), and liver disease (e.g., alcoholism).
Normocytic anaemias are characterised by RBCs within the normal size range (mean corpuscular volume, 80 to 98 fL) and include anaemias of acute blood loss, acquired and inherited haemolytic anaemias (e.g., sickle-cell anaemia), mixed micro-macrocytic anaemias, and anaemias related to renal failure and bone marrow disease.
Aetiology / Risk Factors
Anaemia is caused by decreased production of RBCs resulting from deficiencies in the elemental ingredients necessary for RBC production; increased destruction of RBCs (haemolysis) due to defects in the RBC or environmental stressors; and from excessive bleeding.
Decreased production of RBC is caused by the following:
-
Menstruation (monthly iron losses, 20 to 30 mg/month)
-
Pregnancy (iron losses from increased needs and losses at the time of delivery) and lactation
-
Iron, folic acid, vitamin B12
-
Erythropoietin deficiencies (e.g., due to kidney disease or drugs)
-
Chronic disease states (e.g., rheumatoid arthritis, inflammatory bowel disease, renal failure)
-
Inherited anomalies (e.g., thalassaemias)
-
Gastrointestinal blood loss (e.g., ulcers, cancer, parasites)
-
Genitourinary blood loss (e.g., pregnancy, uterine bleeding, menstruation)
-
Overt blood loss (e.g., after surgery, or regular blood donations)
-
Malabsorption syndromes (e.g., coeliac disease)
-
Neoplasia
-
Excess alcohol ingestion
Increased destruction of RBC is caused by the following:
-
Inherited anomalies (e.g., membrane, enzyme, or haemoglobin anomalies)
-
Environmental stresses (e.g., antibody deposition, parasitic infection)
-
Oxidant drugs (e.g., antibiotics, antimalarials, analgesics)—specific to patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency
Symptoms and Signs
There is tremendous variability between individuals in the clinical manifestations of anaemia, which depend on the cause, severity, onset, and any underlying disease process. Generally symptoms occur when there is an acute drop in haemoglobin to 70 to 80 g/L. However, if anaemia develops slowly, patients may be able to tolerate haemoglobin levels as low as 60 to 70 g/L before becoming symptomatic.
-
Fatigue, headache, dyspnoea (shortness of breath), light-headedness
-
Pain in the abdomen and back, palpitations and angina
-
Episodic jaundice and dark urine (i.e., hemoglobinuria)—specific to sideroblastic anaemia
-
Pica (cravings for strange foods) and koilonychia (thin, concave nails)—specific to iron-deficiency anaemia
-
Glossitis, jaundice, loss of vibratory and position sense, and neurologic symptoms, which may be permanent—specific to pernicious anaemia (i.e., vitamin B12 deficiency)