Classification of anaemia

The various types of anaemia are classified in terms of the red cell size—the mean corpuscular volume (MCV).

Note: Upper limit of MCV varies from 95-100 depending on age and laboratory.

Table 19.2 outlines a classification of some of the more common causes of anaemia encountered in general practice. There can be an interchange of disorders between the above groups, e.g. the anaemia of chronic disorders (chronic infection, inflammation and malignancy) can occasionally be microcytic as well as normocytic; the anaemia of hypothyroidism can be macrocytic in addition to the more likely normocytic; the anaemia of bone marrow disorder or infiltration can also be occasionally macrocytic.

Table 19.2 Selected causes and investigations of anaemia

Causes/classification

Primary diagnostic feature

Secondary investigations

Microcytic (MCV < 80 fL)

Iron deficiency

Haemoglobinopathy e.g. thalassaemia

Sideroblastic anaemia (hereditary)

s.Fe I s.ferr I transferrin Therapeutic trial of iron; GIT T evaluation for blood loss s.Fe N; s.ferr N or Î s.Fe N; s.ferr N or Î

Haemoglobin investigation Bone marrow examination

Occasionally microcytic

Anaemia of chronic disease (sometimes microcytic)

Macrocytic (MCV > 98 fL)

Specific for underlying disorder

With megaloblastic changes Vitamin B12 deficiency

Folate deficiency Cytotoxic drugs

(b) Without megaloblastic changes

Liver disease/alcoholism

Myelodysplasie disorders (including sideroblastic anaemia)

Normocytic (MCV 80-98 fL)

Acute blood loss/occult Anaemia of chronic disease 1 Haemolysis

Chronic renal disease Endocrine disorders s.B12 I rc/Fol N or î

Appropriate setting; s. B12N; rc.Fol N

Appropriate setting; uniform macrocytosis; s. B12N; rc.Fol N

Specific peripheral blood findings; s.B12N; rc.Fol N

Isolated anaemia; Retic T Appropriate setting; Retic i

Specific red cell changes; Retic T

Isolated anaemia; Retic i Appropriate setting; isolated anaemia; Retic i

IF antibody assay; Schilling test

Usually none None

Liver function tests

Bone marrow examination

Dictated by clinical findings s.Fe I and s.ferr N or î s.Bil and s.LDH î s.hapt I specific tests for cause Renal function Specific endocrine investigation

Abbreviations: MCV = mean corpuscular volume; s.Fe = serum iron; s. ferr = serum ferritin; s.B12 = serum vitamin B12; rc.Fol = red cell folate; IF = intrinsic factor; Retic = reticulocyte count; s.Bil =

serum bilirubin; s.LDH = serum lactate dehydrogenase; s.hapt = serum haptoglobin; N = normal; i : reduced; T = elevated

Source: Adapted from Anaemia, MIMS Disease Index, 1 with permission of MIMS Australia, a division of MediMedia Australia Pty Limited

Microcytic anaemia — MCV < 80 fL

The main causes of microcytic anaemia are iron deficiency and haemoglobulinopathy, particularly thalassaemia. Consider lead poisoning.

Iron-deficiency anaemia

Iron deficiency is the most common cause of anaemia worldwide. It is the big cause of microcytic anaemia with the main differential diagnosis of microcytic anaemia being a haemoglobinopathy such as thalassaemia.

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