ABC of CBC - ABC of CBC Is it so simple? Dr. Sanwar Agrawal...

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Unformatted text preview: ABC of CBC Is it so simple? Dr. Sanwar Agrawal MD Ekta Institute of child health Raipur PUBLISHED BY Yes, it is! The complete blood count (CBC) is a deceptively simple test to order and interpret Provided, You concede that it is difficult to be Provided, simple. simple. The CBC is a bargain; its cost can be much less than modern imaging studies, but like the modern imaging studies, its value is lost without appropriate analysis. Because of explosion of new technology and information, understanding of and sophisticated use of the CBC will take on added importance. What is CBC? Measured parameters: Hemoglobin, MCV, and Hemoglobin, erythrocyte count erythrocyte Hemoglobin Hemoglobin concentration is measured by absorbance spectrophotometry and relies on complete lysis of erythrocytes. Platelets, WBC Derived parameters: Derived MCH, MCHC, and hematocrit hematocrit The hemoglobin, MCV and RBC count are the measured parameters The technique electric impedance electric Flow cytometry Impedance Erythrocyte counting and size Erythrocyte determination are accomplished by passage of cells through an electric field created by direct current As the cells pass singly through As the field, a small resistance is generated that is measured as a pulse height. From the pulse height, the size and number of erythrocytes are determined. These data are frequently plotted as a histogram in the typical modern Coulter-type electric impedance instrument Flow cytometry With the Advia, red cells With are sphered in a diluent and then passed through a laser. The cells scatter light (at different angles) which is detected by the instrument (see image to the right). The laser detects the number of cells, cell volume (using low angle scatter) and internal content, i.e. hemoglobin concentration (using high angle scatter) by light scatter. The rule of 3 the measured hemoglobin concentration is the approximately three times the RBC count, and the calculated hematocrit is three times the hemoglobin value. When significant deviation occurs from these approximate calculations, artifacts in the CBC should be suspected artifacts ARTIFACTS IN ELECTRONIC ARTIFACTS CELL COUNTING CELL Cause Hb Hct Cold agglutinins Cold RBC -- -- -- Hyperleukocytosis Hyperosmolar plasma- MCV MCH MCHC --- -- -- -- Spun V/S Automated Hct. Spun > Automated. Spherocytes, sickle erythrocytes, hypochromic cells, Spherocytes, and reticulocytes, trap more plasma. To permit close correlation between the manual and To automated hematocrits, a correction factor of approximately 3% is applied to the calculation of the hematocrit . hematocrit A case can be made to dispense with reporting a calculated hematocrit with the CBC because the hemoglobin value that is measured directly is more reliable MCV The mean cell volume The indicates the volume of the "average" red cell in a sample. It is expressed in -15 femtoliters (fl; 10 -15 liters). With impedance analyzers, the MCV is measured by averaging the amplitude of the pulses created as the cells pass the aperture of the counter. MCV The instrument using The scattered light also plots the cell volume and hemoglobin concentration together in a together volume/hemoglobin (V/HC) cytogram. Normal red blood cells with Normal normal volume (normocytic) and hemoglobin concentration (normochromic) are found in the middle box MCV Agglutinated cells (arrow) Agglutinated with IHA form a distinct cluster (macrocytic normocluster chromic) above the normal chromic) red cells (arrowhead) A. Normal RBC V/H A. cytogram B. Polychromasia: the polychromatophils form a discrete cluster (arrow) that extends off the normal red cell population (arrowhead) and is macrocytic and hypochromic. Micro and Macrocytes Neonate MCV > 100 fl. After 6 months age : 70+ age in years ( lower After limit of normal) limit 84+0.6 x ( age in years)= upper limit of 84+0.6 normal. normal. Corresponding adult values are 80 and 96 Corresponding respectively. respectively. Mean Cell Hemoglobin Mean This represents the absolute amount of hemoglobin in This the average red cell in a sample. The MCH is calculated from the [Hb] and the RBC The using the following equation: using MCH (pg) = (Hb x 10) ÷ RBC This value is generally not useful This A low MCH could be due to smaller than normal low cells with normal Hb concentration, or normal sized cells with lower than normal Hb concentration Mean Cell Hemoglobin Mean Concentration (MCHC) MCHC is the mean cell hemoglobin concentration, MCHC expressed in g/dL It can be calculated from the [Hb] and the PCV using It the formula: MCHC = (Hb ÷ PCV) x 100. the The normal value for MCHC is about 33%. The Values for MCHC significantly above the reference Values above range are not physiologically possible due to limitations on the solubility of Hb. For all practical purposes a MCHC > 35% and RDW >14 is Spherocytosis Red Cell Distribution Width (RDW) Red The RDW is an index of the The variation in cell volume within the red cell population. RDW = (Standard deviation RDW of red cell volume ÷ mean cell volume) x 100 Red cell populations with Red higher than normal RDW are termed heterogenous; heterogenous those with normal RDW are homogeneous. homogeneous It’s a measure of It’s anisocytosis anisocytosis RDW….. In some instances, the RDW is the first test In result to increase with changes in red cell population sizes. In early iron deficiency, there are only low In numbers of microcytic red blood cells. This will increase the standard deviation and the RDW, but the mean cell volume is unchanged because there are insufficient numbers of microcytic cells to change the mean volume mean MCV and RDW MCV low MCV normal MCV high RDW RDW normal normal Thalassemia Chronic Thalassemia Chronic trait disease trait disease Aplastic Aplastic anemia anemia RDW RDW high high Iron Iron deficiency deficiency Folate/B12 Folate/B12 def def IHA Early Early Iron/folate def Iron/folate Myelofibrosis Microcytosis and raised TRBC Only 3 conditions: B Thal Trait, Hypoxic Only erythrocytosis, Polycythemia vera. erythrocytosis, RDW is normal in first and increased in rest. For pediatric age group: Microcytosis, raised For TRBC and normal RDW is B Thal trait. TRBC Platelets A low counts should be low cross checked manually. cross Small RBCS (like in Small IDA) may be counted as platelets ( One explanation for increased Plt in IDA). increased Platelet clumps are Platelet responsible for low counts. counts. 1. Platelets 2. Large platelets 3. Red blood cells 4. RBC fragments 5. Debris 6. Ghosts MPV Large Platelets: Macrothrombocytes (MPV >10 fl) Idiopathic Thrombocytopenic Purpura Idiopathic Purpura Bernard-Soulier Disease Bernard-Soulier May-Hegglin Anomaly May-Hegglin Small Platelets: Microthrombocytes (MPV <6 fl) Aplastic Anemia Wiskott-Aldrich Syndrome Wiskott-Aldrich Thrombocytopenia-absent radii (TAR Syndrome) -absent Storage Pool Disease Storage WBC Nucleated red blood cells are counted by all Nucleated hematology analyzers (regardless of technique) as white blood cells. For this reason, the white blood cell count must be corrected for the number of nucleated red blood cells in the circulation. To correct a leukocyte count, the number of NRBCs per 100 leukocytes is recorded during the differential leukocyte count. Then a correction is made as follows: follows: Corrected WBC = nucleated cell count x (100 ÷ Corrected [nRBC + 100]) In this cytogram, the cells are displayed as a worm, with the mononuclear cells (lymphocytes and monocytes) in the head and the granulocytes (neutrophils) in the body of the worm. A. Neutrophils B. Monocytes C. Lymphocytes D. Eosinophils E. Large unstained cells F. Platelets/noise G. Debris/noise CBC IS A LAUGHING GAME THANKS! For more lectures visit ...
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