Iron, TIBC and Saturation
Table 1: Reasons for iron deficiency
Table 2: Stages of iron deficiency
Table 3: Patterns in hypochromic/microcytic anaemia
Iron deficiency occurs in several stages with anaemia as a late manifestation. Patients usually present with the insidious onset of anaemia, although the haemoglobin level correlates poorly with symptoms. If a patient has symptoms of easy fatigability or lethargy in the presence of a history suggestive of iron deficiency, it is reasonable to perform a ferritin estimation even if the FBC is normal. The blood film changes may be subtle and easily missed and even if the Hb level is within the normal range, it may be low for the particular patient.
Diagnosing Iron Deficiency(top)
Examination of the full blood count and blood film will usually suggest the diagnosis. The classical picture is that of a hypochromic/microcytic anaemia although in the early stages, careful examination of the blood film may show a small population of hypochromic/microcytic cells in a patient with normal red cell indices. It should be emphasised that not all hypochromic/microcytic anaemias are due to iron deficiency. The Red Cell Distribution Width (RDW) is a useful parameter in differentiating iron deficiency from thalassaemia minor by providing a measure of variation in red cell size. In thalassaemia minor, the RDW is usually normal as the population of cells are relatively uniform, whereas in iron deficiency, the value is usually >14.5%.
Serum Ferritin Measurement(top)
Serum ferritin is the most useful test in the diagnosis of iron deficiency. In healthy people, it accurately reflects iron stores; a level below normal is diagnostic of iron deficiency. In an anaemic patient a normal level is less useful as many diseases, such as malignancy, liver disease and inflammatory diseases, cause a rise in ferritin independent of iron stores. In such patients, a low level can be considered to be diagnostic of iron deficiency and the diagnosis is virtually excluded if the level is above normal. In patients with indeterminate ferritin levels and anaemia, the gold standard for the assessment of storage iron is marrow aspiration and Prussian blue staining. Alternatively, a therapeutic trial of oral iron will confirm the diagnosis if a reticulocytosis (at one week) and a rise in haemoglobin (usually in the order of 0.5 to 1.0 g/week) are found.
Serum Iron, Transferrin and Transferrin Saturation Measurement
Although measurement of serum iron, transferrin (a measure of serum total iron binding capacity) and transferrin saturation will show a characteristic pattern in iron deficiency, there is considerable overlap with values found in various disease states; therefore these measurements have only a supportive role in diagnosis. Although serum iron is often requested and is usually reduced in iron deficiency, it is raised by recent food intake (and, therefore, must he assessed on a fasting specimen) and is reduced in many common disorders which give rise to the anaemia of chronic disease. There is also a marked diurnal variation with lower levels occurring in the evening. Interpretation of a correctly collected specimen also requires a knowledge of the transferrin level. The typical patterns of iron and transferrin in different disease states are shown in the table.
Common Mistakes in the Diagnosis of Iron Deficiency(top)
Common mistakes are:
For further information please contact Dr Tony Dodds or Dr Joanne Joseph 8382-2378
|Last updated 13/03/2006|