Hypochromic Microcytic Anaemia
Shown above is an image of hypochromic microcytic anaemia. This patient had iron deficiency anaemia. Microcytosis is presence of small erythrocytes and hypochromia presence of erythrocytes that are poorly haemoglobinized. The nucleus of a small lymphocyte, the cell in the centre of the image, is a good guide to the size of erythrocytes on a peripheral smear. The nucleus has a diameter of 8.5 µm and a normal erythrocyte a diameter of 7.5 µm. The erythrocytes in in the image are substantially smaller than the lymphocyte nucleus. Erythrocytes have a central pale staining area which occupies about one third of erythrocyte diameter. As the cells get less haemoglobinized the central pale staining area increases. Many of the erythrocytes in the image above have a pale staining area occupies all but a thin rim at the periphery. In others, the pale staining area is increased. The erythrocyte sizes vary. Anisocytosis, increased variation in erythrocyte size, a feature of iron deficiency anemia, is evident in the image.
The investigation to diagnose iron deficiency include:
- Haemoglobin and red cell parameters
- Bone marrow iron staining
- Serum Iron, total iron binding capacity and transferrin saturation
- Serum ferritin
- Zinc Protoporphyrin
- Soluble transferrin receptor
Haemoglobin and Red cell Parameters
Patients undergo evaluation for iron deficiency because they are anaemic. Latent iron deficiency is characterized by a progressive decrease in bone marrow iron stores in patients who have yet not developed symptoms. These patients are asymptomatic and latent iron deficiency is not a clinical problem. Iron deficiency causes microcytic hypochromic anaemia. There are no reliable test to differentiate iron deficiency from other causes of microcytic hypochromic anaermia. The red cell indices that have been proposed to be useful include
- Red cell distribution width (RDW): RDW is a measure of anisocytosis. Iron deficiency anaemia shows more anisocytosis than β-thalassaemia and is associated with a higher RDW. The promise held out by RDW to differentiate iron deficiency and thalassaemia has not fulfilled.
- Reticulocyte haemoglobn content: Changes in erythropoiesis are reflected earliest in the reticulocyte. Reticulocytes form a small fraction of erythrocytes. Change in reticulocyte indices do not change erythrocyte indices. Some automated counters are able to measure reticulocyte indices. Reticulocyte haemoglobin content falls with iron deficiency anaemia but the finding is not specific. It has been found to asses iron deficiency in patient of chronic renal failure being treated with erythropoietin accurately. It has not been found to be useful in diagnosing iron deficiency in patients with thalassaemia.
Bone Marrow Iron Staining
Bone marrow is stained for iron content by the Prussian blue reaction and graded in a semiquantative method. Bone marrow iron is the gold standard for diagnosis of iron deficiency. The test is invasive and suffers from an inter-observer variation. Bone marrow iron staining is resorted to only when diagnosis can not be reached by other methods.
Serum iron, total iron binding capacity and transferrin saturation
Iron deficiency is diagnosed by a transferrin saturation of less than 16%. The serum iron is low and the total iron binding capacity is usually increased. Patients with low total iron binding capacity have anaemia of chronic disease if the transferrin saturation is ≥16% or iron deficiency along with anaemia of chronic disease if the transferrin saturation is <16%.
Ferritin is one of the iron storage proteins. Serum ferritin levels co-relates with body iron content. A ferritin level less than 12ng/mL is diagnostic of iron deficiency. Inflammation increases ferritin. Chronic inflammatory diseases like rheumatoid arthritis and ulcerative colitis have anaemia of chronic disease and may also have iron deficiency. A patient with iron deficiency in the setting of an inflammatory disease may not have a low ferritin. There is no consensus for diagnosing iron deficiency in patients with anaemia of chronic disease. Inflammation rarely increases the serum ferritin values more than 60-100ng/mL. Iron deficiency can be excluded in patients with ferritin above this cutoff.
Iron is added to propoporphyrin in the final step of heme synthesis. Zinc takes the place of iron in patients with iron deficiency. A rise in the concentration of zinc protoporphyrin is the earliest manifestations of iron deficiency. Zinc protoporphyrin levels rise in about 2 weeks from the onset of iron deficiency and need more than a month to normalize after restoration of normal iron levels.
Soluble transferrin Receptor
Iron deficiency results in an increase in soluble transferrin receptor (sTfR). Inflammation impacts serum ferritin but not sTfR making it a potentially useful investigation for differentiating anaemia of chronic disease and iron deficiency. The assay has been difficult to standardize. A ratio of sTfR/log ferritin is more useful.
The sTfR levels reflect the density of transferrin receptors cells and number of cells. sTfR increases when there is erythroid hyperplasia due to any cause like haemolytic anaemia and may not reflect iron deficiency in these disorders.
In 1912 Plummer described dysphagia and spasm of the upper oesophagus without anatomical stenosis in patients with longstanding iron deficiency. In 1919, Vinson, Paterson and Kelly independently described patients with similar findings. The triad of iron deficiency anaemia, dysphagia and oesophageal webs has been called Plummer-Vinson syndrome or Paterson-Kelly syndrome (depending in the side of Atlantic you reside) after these physicians. It is a rare disease possibly related to iron deficiency and is also known as sideropenic dysphagia.
Etiology and Pathogenesis
Etiology of Plummer –Vinson syndrome is not known, iron deficiency is the most likely cause but malnutrition and genetic predisposition may contribute. Plummer-Vinson syndrome has been associated with coeliac disease, thyroiditis and rheumatoid arthritis raising the possibility of autoimmunity playing a role in Plummer-Vinson syndrome.
The oesophagus of patients with Plummer –Vinson syndrome shows webs at the junction of the hypopharynx and oesophagus, usually extends backwards from the anterior wall. The webs may take a cuff shape and the opening may be reduced to a pinhole. Oesophageal stricture may be seen. Histologically the webs are made of normal oesophageal epithelium, sometimes with chronic inflammation.
Plummer –Vinson syndrome is a mainly affects women in the fourth to the seventh decade of life but has been described in other age groups. The patients present with gradual onset of dysphagia, initially for solids. Examination reveals evidence of iron deficiency including pallor, koilonachia, glossitis and cheilosis. Splenomegaly and thyroid enlargement may occur.
The webs are best demonstrated videofluoroscopically by a barum swallow. Endoscopically they appear as 2-3mm smooth grey thin extension of normal mucosa usually with an eccentric lumen. Endoscopy can rupture the webs and the scope should be introduced under direct vision. Laboratory investigations show hypochromic microcytic anaemia, low transferrin saturation and low serum ferritin characteristic of iron deficiency.
The iron deficiency should be treated. Dysphagia may be treated by dilatation or endoscopic disruption using a biopsy forceps. The prognosis is good. Patinets with Plummer –Vinson syndrome are predisposed to carcinoma of pharynx and oesophagus and a close follow up of patients is needed.