October 30, 2010

PLAB Question 22

Consider these values - MCV: Decreased; Serum ferritin: Decreased; Total iron binding capacity: Increased; Serum iron: Decreased; Marrow iron: Absent

a) Thalassaemia trait
b) Hypoparathyroidism
c) Hereditary sideroblastic anaemia
d) Protein energy malnutrition
e) Chronic renal failure
f) Anaemia of chronic disease
g) Acute blood loss
h) Iron deficiency anaemia
i) Oral contraceptives
j) Megaloblastic anaemia

The correct answer is H

Iron deficiency anaemia or IDA is recognized from the combination of abnormal iron-supply studies and microcytic, hypochromic red blood cell morphology. The [serum iron] SI falls to very low levels [<4 mol/L (<30 g/dL)], while the total iron binding capacity [TIBC] increases. The ferritin level is always less than 15 g/L.

Once the patient's hemoglobin level falls below 100 to 110 g/L (10 to 11 g/dL), poorly hemoglobinized cells begin to enter the circulation.

When the anaemia is only of moderate severity, the cells tend to be microcytic but not hypochromic. At lower hemoglobin levels, both microcytosis and hypochromia become more pronounced.

Furthermore, red blood cell production becomes increasingly ineffective, resulting in greater degrees of aniso- and poikilocytosis. With very severe iron-deficiency anaemia , cigar- or pencil-shaped red blood cells may be observed.

As a rule, target cells are not seen with iron deficiency. When present, they suggest a globin chain production defect, i.e. one of the thalassemias. They may also be seen in the presence of liver disease.

The more common diagnostic problem is the potential confusion between iron deficiency and an inflammatory block in iron delivery from the reticuloendothelial system to the erythroid progenitors [the anaemia of chronic disease or AoCD]. However, while both the SI and TIBC decline in patients with AoCD, the TIBC is increased in iron deficiency anaemia while the SI is decreased. However, serum ferritin is increased in AoCD where it is decreased in iron deficiency anaemia and if a marrow aspiration is performed, AoCD will show normal to increased iron stores together with a hypoproliferative marrow morphology. Moreover, in anaemia of chronic disease [AoCD] patients typically show a low SI, low TIBC, a normal to high serum ferritin level.

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