Differential
Diagnosis Of Hypochromic
 |
| Table 3.7 Laboratory diagnosis of a hypochromic anaemia. |
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.
