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Laboratory Examinations In Detecting Anemia And An Overview Of Macrocytic (Megalobastic) Anemia
A Medical Laboratory
Hemoglobinometry And Blood Counts
The following investigations are carried out to detect the severity and type of anemia.
Hemoglobinometry and blood counts:
The standard procedure is the cyanmethhemoglobin method using a reliable standard for comparison. When the hemoglobin level is below 12g/dl, full investigations should be undertaken. Absolute counts of erythrocytes, leucocytes and platelets and calculation of the erythrocyte indices should be done by automatic machines which are accurate. Results obtained by using manual methods are only approximate.
Packed cell volume (PCV-hematocrit) is a reliable parameter which should be done in all cases. The mean corpuscular hemoglobin concentration:
MCHC = [Hb in g/dl X 100]
Helps in determining the type of anemia in a borderline case and also in the follow up of the case. Values below 27g/dl suggest microcytic hypochromic types.
Laboratory Investigations Ongoing
Examination Of Blood Smear
This is the easiest and reliable method to determine the morphology of erythrocytes. Microcytic hypochromic erythrocytes are smaller than normal. (normal mean corpuscular diameter (MCD) is 7.5+0.3 uml) and the center is empty with only a ring of hemoglobin taking up the stain. Considerable anisocytosis and poikilocytosis are seen. Macrocytic erythrocytes are larger with the center also showing uniform staining. Normocytic normochromic erythrocytes are normal in size and staining. Reticulocytes appear as polychromatophilic macrocytes in Romanowski stained films, but when stained in the fresh state with brilliant cresyl blue, the cytoplasmic reticulum is visualized. Normal value for reticulocyte in Indian subkects is 0.5 to 2.5%. Anisocytosis, poikilocytosis, polychromasia and reticulocytosis indicate active regeneration of erythrocytes. When erythropoiesis is very much accelerated, normoblasts may appear in peripheral blood. In myelophthisic anemias normoblast may be released from the bone marrow even without active regeneration of erythrocytes.
In aplastic anemia, leukemia and megaloblastic anemia, the leucocytes also show morphological changes which are diagnostic. The changes in platelets may be helpful in diagnosis. In microcytic hypochromic anemia, presence of excess platelets generally suggests blood loss. Thrombocytopenia indicates the possibility of hypoplastic anemia. In the tropics, special attention should be given to detect malarial parasites in all cases.
Examination Of Bone Marrow
Examination of bone marrow are suspected In all cases of anemia where the cause is not obvious or where hemolysis, neoplasia or aplasia should be examined as a first line of investigation. This helps to confirm the morphological type as well as to detect the cause.
The defect of DNA synthesis is most pronounced in marrow cells, but it is also present in varying degrees in all rapidly proliferating cells. The nucleus of the megaloblast has a finer reticular pattern which distinguishes it from normoblast. Megaloblastic anaemia is common in nutritional deficiency of folate or vitamin B12 or when the metabolic pathways of these nutrients are blocked.
Nutritional Megaloblastic anaemia (NMA)
This is the most common form of megaloblastic anaemia and is caused by the deficiency of folic acid, vitamin B12 or both. Folate deficiency is more frequent than vitamin B12 deficiency in all parts of Africa and Asia. In many cases, there is also iron deficiency and so the blood picture is dimorphic.
Causes of megaloblastic anaemia
I. Those caused by inadequate supply of folic acid, vitamin B12 or both
a. Nutritional deficiency b. Increased demand such as pregnancy, infancy and infection c. Protein caloric malnutrition d. Malabsorption states e. Drugs with antifolate action eg, phenytoin, methotraxate f. Total gastrectomy or extensive lesions involving the stomach g. Infestation with the tape worm Diphyllobothrium latum
II. Acquired vitamin B12 malabsorption in Addisonian pernicious anemia which is due to deficiency of the gastric intrinsic factor
A Megaloblastic Anemic Patient
Diagnostic Algorithm For Macrocytic Anemia
Macrocytic Anemia In General
These constitute about 5% of nutritional anaemias seen in developing countries. In these, the red cells are larger in size. The mean corpuscular volume reaches above 110 fl or more. These cells are usually full hemoglobinised and MCHC is normal. Mean corpuscular hemoglobin is increased. In some cases, the macrocytes may also be hypochromic due to concomitant deficiency of Iron (dimorphic). Common cause of macrocytosis in developing countries is deficiency of folic acid and or vitamin B12. In the absence of these vitamins, DNA synthesis is abnormal. Megaloblastosis results when DNA synthesis is impaired in the presence of normal RNA and protein synthesis. Synthesis of protein, RNA and hemoglobin continues in the cytoplasm. When DNA synthesis is impaired, cell division is retarded but the cell grows more in between mitotic cycles and hence the megaloblasts are larger in size. As the deficiency becomes more pronounced, many early forms of erythroblasts are destroyed in the marrow and ultimately erythropoiesis becomes almost totally ineffective.
Macrocytic anaemias may be associated with megaloblastic erythropoiesis or normoblastic erythropoiesis. Macrocytic anaemia with normoblastic marrow is seen when there are numerous reticulocytes in peripheral blood. Other less common causes include hypothryroidism, liver disease, renal failure and chronic infections.
© 2014 Funom Theophilus Makama