Lab 05 PCV and blood cell indices PDF

Practical Animal Physiology................................................................................................. Lab. 5 Blood Physiology: Packed Cell Volume (PCV) and Red Blood Cell Indices Purpose Packed cell volume (hematocrit) and red blood cell (RBC) indices are part of t...

Practical Animal Physiology................................................................................................. Lab. 5 Blood Physiology: Packed Cell Volume (PCV) and Red Blood Cell Indices Purpose Packed cell volume (hematocrit) and red blood cell (RBC) indices are part of the complete blood count test. They are used to help diagnose of anemia or polycythemia. Background The whole blood is comprised of erythrocytes, platelets, and leukocytes. The cells are suspended in the plasma. In blood from healthy individuals, erythrocytes constitute the vast majority of cells. Plasma mainly consists of water (approximately 93%) but also of salts, various proteins, and lipids as well as other constituents such as, glucose. Hematocrit literally means 'blood separation'. It measures the percentage(%) of volume of packed RBCs. Therefore, hematocrit is also known as packed cell volume (PCV). When heparinized whole blood is centrifuged in a glass tube, the heavier elements of the blood, such as the red blood cells, settle to the bottom of the tube, and the lighter elements contained in the plasma remain near the top. The percentage of the total blood volume in the tube occupied by the packed red blood cells is known as the hematocrit, in between plasma and RBCs there is a layer called buffy coat which contains (WBC and platelets). The manually estimated PCV is more reliable than the manually performed red cell count, because much less error is associated with determination of hematocrit. Normal hematocrit values: Age Hematocrit % At birth (newborn) 53-65% 6-12 months 33-40% Adult males 42-52% Adult females 35-47% Increased PCV is seen in::  All cases of polycythemia (newborns, high altitude), hypoxia due to lung and heart diseases.  Congestive heart failure, burns (loss of plasma), dehydration, after severe exercise, and emotional stress. In all these cases, there is a change in the plasma volume, or redistribution of red cells. 1 Practical Animal Physiology................................................................................................. Lab. 5 Decreased PCV is seen in  All types of anemia.  Pregnancy (due to hemodilution), and ingestion of large amounts of water.  The hematocrit is used in the detection and classification of various types of anemias along with other parameters (hemoglobin and red cell count) of red cell indices. Red cell indices are used to detect abnormalities in erythrocyte size, shape, and color. Three commonly used indices are the mean corpuscular volume (MCV), the mean corpuscular hemoglobin (MCH), and the mean corpuscular hemoglobin concentration (MCHC) Morphology of RBCs A normocytic erythrocyte is normal in size and shape; a normochromic erythrocyte is normal in color (and thus in hemoglobin content). A microcytic erythrocyte is smaller than normal; a macrocytic erythrocyte is larger than normal. A hypochromic erythrocyte is paler than normal (indicating insufficient hemoglobin); a hyperchromic erythrocyte is deeper in color than normal. Anisocytosis is a variation in size, poikilocytosis is a variation in shape. The optimum situation is for erythrocytes to be normocytic and normochromic. Methods of determination Red cell indices are determined by two methods: 1) indirectly by calculating the indices from PCV, hemoglobin, and red cell count. 2) directly by automated counting. Calculation of red cell indices 1. Mean corpuscular volume (MCV): MCV is the average volume of a red cell expressed in femtoliters (1 fl = 10-15 L). Where factor 10 is introduced to convert the hematocrit reading (in percent) from the volume of packed cells per 100ml to volume per liter. Normal value: The MCV in normal adults is 78-96fl. The MCV indicates whether the RBCs are microcytic, normocytic, or macrocytic. 2  Practical Animal Physiology................................................................................................. Lab. 5 2. Mean corpuscular hemoglobin (MCH): The MCH is the average weight of hemoglobin content in a red cell expressed in picograms (1 pg = 10-12 g). Normal value: The normal range for MCH is 27-33pg. A low MCH indicates microcytosis, hypochromia, or both. A high MCH suggests hyperchromia. It may be as low as 20pg or less in the hypochromic microcytic anemia. This is seen in iron deficiency and thalassemia minor or as high as 50pg in macrocytic anemia 3. Mean corpuscular hemoglobin concentration (MCHC): The MCHC is an expression of the average hemoglobin concentration per unit volume of packed red cells. It is expressed as a percent. Normal value: The normal range for MCHC is 30-37%. Procedure- Hematocrit (Microhematocrit Method) 1. Lance your fingertip to obtain a drop of blood. Wipe away the first drop of blood because it dilutes the sample with tissue fluid. 2. Fill the capillary tube (heparinized) two-thirds to three-quarters full with fingertip blood. 3. Seal one end of the tube with clay. 4. Place the filled tube in the micro-hematocrit centrifuge with the plug end to the outside. 5. Centrifuge at high speed (10000 rpm) for 5 minutes. 6. Read the hematocrit by placing the tube in the micro-hematocrit reader. Figure 1hematocrit reader 3