Features of peripheral smear like erythrocyte size, haemoglobinization and variability in size have long been useful in evaluation of patients with anaemia. The definitions of these parameters before the advent of haematological counters were subjective. The haematological counters have allowed an accurate measurement of erythrocyte size and numbers allowing reliable determination of mean cell volume (MCV), mean cell haemoglobin (MCH) and mean cellular haemoglobin concentration (MCHC). Mean cellular volume is used to classify anaemias (see Evaluating Anaemias). MCV is of little value in differentiating two of the commonest causes of anemia, iron deficiency and β-thalassaemia trait as both are microcytic hypochromic.
Anisocytosis is and abnormal variation in erythrocyte size. It is a feature of nutritional deficiencies, myelofibrosis, bone marrow infiltrations, microangiopathic haemolytic anaemia and in the presence of erythrocyte aggregates. Thalassaemias do not show anisocytosis. The erythrocyte is a disc approximately the diameter of the nucleus of a small lymphocyte and the central one-third is pale. The assessment of anisocytosis is subjective. Red cell distribution width(RDW) is quantitation of aniscytosis.
Standard deviation of a parameter is a measure of its scatter from the mean. MCV is an average of erythrocyte volumes measured by the counter. RDW is the standard deviation of these observations. It is expressed as a percentage of MCV. The normal values are 11.5-14.5%. High RDW means more anisocytosis.
Despite the apparent promise RDW has a limited role in diagnosis. A normal RDW in a microcytic anaemia can suggest the presence of on thalssaemia but can not be relied on as a sole criteria for separating iron deficiency from thalassaemia. The presence of a high RDW should alert one to the presence of one of the causes of anaemia listed above but again RDW can not be relied on for making a final diagnosis of any of these conditions. Blood transfusion in an anaemic patient increases the RDW.
Development of erythrocytes involves coordinated changes in the nucleus and the cytoplasm of erythroid processors (see Morphology of Erythroid Precursors) . The proerythroblast is a large cell with a fine chromatin, the earliest forms not being different from other blasts. As the cell matures the chromatin becomes more clumped and the nucleus reduces in size and the cytoplasm becomes acidophilic. Finally a dark pyknotic nucleus is extruded from the orthchromatophilic normoblast to give a reticulocyte.
Figure 1. Basophilic Normoblast
A group of basophilic normoblast are shown above. The cytoplasm is basophilic and the chromatin more clumped than a proerythroblast. The two cells on the right are less mature than the two on the left.
Figure 2. A group of orthochromatophilic normoblasts
The figure above show a group of orthochromatophilic normoblasts. The cells of the left are more mature. The nucleus is reduced to a dense body in the more mature forms. The cytoplasm still has a blue tinge. which contrasts from the megaloblasts shown below.
Figure 3. Basophilic, polychromatophilic and orthochromatophilic normoblasts
The figure above shows three stages of erythroid maturation. The cell on the top right is a basophilic normoblast, bottom right is a orthochromatophilic normoblast and the bottom right is an orthochromatophlic normoblast. Note the evolution of nuclear and cytoplasmic changes.
Figure 4. Megaloblasts
The figure above shows a group of megaloblasts. Cells in the right lower corner have a cytoplasm which is fully haemoglobinized and resembles the mature erythrocyte. These cell still have a nucleus. The cell on the left upper corner has a cytoplasm resembling a orthochromatophilc normoblast (see figure 2 and 3) but nuclear features resembling a basophilic normoblast (figures 1 and 2). Megaloblastic anaemia results from conditions that hamper DNA synthesis (B12 deficiency, folate deficiency, Chemotherapy drugs). The nucleus of a megaloblast thus matures slower than the cytoplasm resulting in cells having a nuclear morphology resembling a previous stage. This, known as nucleo-cytoplasmic dissociation, is the characteristic feature of megaloblastic anaemia.
Haemolytic transfusion reactions: Haemolysis following red cell transfusion occur in two forms. Acute haemolysis occurs within 24 hours, is more serious and usually intravascular. Delayed haemolysis occurs after the first 24 hours is more common, less serous and usually intravascular.
Febrile reaction: A rise of temperature usually with chills by more the 1°C after blood transfusion. Headache nausea and vomiting may be seen in serve reaction. Fever lasting more the 18 hours after transfusion are not likely to be febrile reactions. They are almost always seen with cellular components being most common with platelet transfusion.
Urticarial Reactions complicate about 1% of blood trasnfusions
Anaphylactic reactions occur in about 1:150,000 patinets. They are seen in patients with IgA deficiency. These patients have anti IgA antibodies that react to IgA in the transfused plasma. These patients must be transfused thoroughly washed RBCs.
Transfusion Induced Acute Lung Injury manifests as sudden deterioration of lung function shortly (2-6 hours) after a blood transfusion. It is treated by respiratory support with oxygenation and positive pressure ventillation.
Graft vs. Host disease is a rare but almost uniformly fatal complication of blood transfusion, usually from a close relative, that manifests as post transfusion fever, skin, liver, and gastrointestinal manifestations and pancytopenia.
Immune suppression caused by blood transfusion has been used in the past for decrease renal graft rejection. Today clinical relevance this effect is not clear.
Hepatitis (B and C): The incidence of transfusion induced hepatitis has called because of testing of blood and blood products.
HIV: HIV posed a major risk before testing became mandatory. Testing has substantially reduced but not eliminated the risk of HIV transmission.
Other Viruses: Cytomegalovirus, Epstein-Barre virus, parvovirus b19, HTLV I, HTLV II can be transmitted by blood transfusion. Though some countries mandate testing for some of these viruses the practice, unlike that for HBV, HCV and HIV is not universal.
Malaria and other parasitic diseases: Out of the parasitic diseases that can be transmitted by blood transfusion (malaria, filariasis, bebesiosis, toxiplasmosis, toxoplasmosis and trypanosomiasis (South American, African). Malaria because of it’s widespread distribution is the greatest concern. because of it’s wide spread distribution.
Transfusion induced sepsis: Transfusion induced sepsis occurs as a result on bacterial growth during storage. It is most common with platelet transfusion as platelets are the only component stored at room temperature.
Coagulopathy: Dilutional coagulopathy due to degradation of labile coagulation factors like V and VIII on storage causes coagulopathy.
Citrate toxicity: Citrate used as an anticoagulant binds calcium and causes hypocalcaemia. Clinically significant hypocalcaemia is seen only with very rapid transfusion raters (more than one unit over less than 5 mins) and in patients with liver disease (because of impaired citrate metabolism). Treated with intravenous calcium.
Hypothermia: Blood is refrigerated for storage. In massive transfusion the urgency and the rapid rate of infusion may result in hypothermia that can be prevented by the use of blood warmers.
Acid-base imbalance: Patients needing massive transfusion are likely to be acidotic due to lactic acidosis. Citrate present in the transfused blood may aggregate acidosis. On recovery citrate and lactate are converted to bicarbonate resulting in metabolic alkalosis the commonest
Hyperkalaemia: Stored blood may have unto 80mEq/L of potassium which on transfusion cause lifethreatening hyperkalaemia
Vein to Vein: An online publication of the Canadian Blood Services
Normal erythrocytes are round disks about 7.5μm in diameter.The central one third is paler than the periphery because of the discoid shape of the erythrocyte. The picture above is a 40X image that shows the uniformity of size and staining of normal erythrocytes. Can one say that the
se cells are 7.5μm in diameter? They could all be 10μm or be 6μm. Is it possible to known about the size of erythrocytes using an unsophisticated laboratory microscope?
The small lymphocyte comes to the rescue! The size of the small lymphocyte nucleus is approximately 8.5μm and it does not vary significantly with disease. The picture above is a 100X image comparing the normal erythrocyte with a small lymphocyte. The cells are slightly smaller than a small lymphocyte. The uniformity of size and that of the pale staining area is evident. Microcytes are smaller erythrocytes and macrocytes larger erythrocytes. Hypochromia is increase in the pale staining area and indicates decreased content haemoglobin. Anisocytosis is increased variability in erythrocyte shape.