Differential Diagnosis Of Hypochromic
Table 3.7 lists the laboratory investigations that may be neces sary. The clinical history is particularly important as the source of the haemorrhage leading to iron deficiency or the presence of a chronic disease may be revealed. The country of origin and the family history may suggest a possible diagnosis of thalassaemia or other genetic defect of haemoglobin. Physical examination may also be helpful in determining a site of haemorrhage, features of a chronic inflammatory or malignant disease, koilonychia or, in some haemoglobinopathies, an enlarged spleen or bony deformities.
In thalassaemia trait the red cells tend to be small, often with an MCV of 70 fL or less, even when anaemia is mild or absent; the red cell count is usually over 5.5 × 1012/L. Conversely, in iron deficiency anaemia the indices fall progressively with the degree of anaemia and when anaemia is mild the indices are normal or only just reduced below normal (e.g. MCV 75–80 fL). In the anaemia of chronic disorders the indices are also not markedly low, an MCV in the range 75–82 fL being usual.
It is usual to perform a serum iron and TIBC measurement, or alternatively serum ferritin estimation, to confirm a diagnosis of iron deficiency. Haemoglobin high‐performance liquid chromatography (HPLC) or electrophoresis with an estimation of Hb A2 and Hb F is carried out in all patients suspected of thalassaemia or other genetic defect of haemoglobin, because of the family history, country of origin, red cell indices and blood film. Iron deficiency or the anaemia of chronic disorders may also occur in these subjects. β‐Thalassaemia trait is characterized by a raised Hb A2 above 3.5%, but in α‐thalassaemia trait there is no abnormality on simple haemoglobin studies so the diagnosis is usually made by exclusion of all other causes of hypochromic red cells and by the presence of a red cell count >5.5 × 1012/L. DNA studies can be used to confirm the diagnosis.
Bone marrow examination is essential if a diagnosis of sideroblastic anaemia is suspected but is not usually needed in diagnosis of the other hypochromic anaemias.