Medical Laboratory Instrumentation Chapter 8 Blood cell counters

Blood cell counter The blood cell counter count the number of RBC or WBC per unit of volume of blood using either of two method: Electrical method called aperture impedance change Optical method called flow cytometry

Blood cell counter Is the determination and the number of the quantity of each type of blood cell : red blood cells, white blood cells, and platelets in a sample of blood in a given sample of blood, often including the amount of hemoglobin, and the proportions of various white cells. . Also called a complete blood counter (CBC).

to identify persons who may have an infection . to diagnose anemia . Purpose The CBC provides valuable information about the blood and to some extent the bone marrow, which is the blood-forming tissue. The CBC is used for the following purposes: to identify persons who may have an infection . to diagnose anemia . to identify acute and chronic illness, bleeding tendencies, and white blood cell disorders such as leukemia . to monitor treatment for anemia and other blood diseases .

Red Blood Cell Count The red cells, the most numerous of the cellular elements, carry oxygen from the lungs to the body's tissues. The red blood cell (RBC) count determines the total number of red cells (erythrocytes) in a sample of blood. Most anemias are associated with a low RBC count, hemoglobin, and White Blood Cell Count The majority of CBCs include both a WBC count and an automated differential. A differential determines the percentage of each of the five types of mature white blood cells. An elevated WBC count occurs in infection, allergy, systemic illness, inflammation, tissue injury, and leukemia. A low WBC count may occur in some viral infections, immunodeficiency states, and bone marrow failure. The WBC count provides clues about certain illnesses, and helps physicians monitor a patient's recovery from others. The differential will reveal which WBC types are affected most. Platelet Count Platelets are disk-shaped structures formed by the detachment of cytoplasm from megakaryocytes. They aid in the coagulation process by attaching or adhering to the walls of injured blood vessels, where they stick together to form the initial platelet plug. A low platelet count may occur in patients with AIDS.

Normal Results CBC values vary by age and sex. Normal values are ultimately determined by the laboratory performing the test. As a guide, the normal values for men and nonpregnant women are as follows: WBCs: 4,500–11,000 per microliter for women and men, with neutrophils representing 50–70%, lymphocytes 25–35%, monocytes 4–6%, eosinophils 1–3%, basophils 0.4–1%, and bands 0–5%. RBCs: 4.2–5.0 million per microliter for women; 4.5–6.2 million per microliter for men. Hemoglobin: 12–15 g/dL for women; 13.6–17.2 g/dL for men. Hematocrit: 35–47% for women; 42–52% for men. Platelets: 150,000 and 350,000 per microliter.

Aperture impedance change When blood is diluted in the proper type of solution, the electrical resistivity of blood cells (ρc) is higher then the resistivity of the surrounding fluid (ρf) By contriving a situation in which these resistivities can be differentiated from each other, we can count cells

Aperture impedance change Blood cell sensing The sensor consist of a two-chamber vessel in which the dilute incoming blood is on one side of barrier, and the waste blood to be discarded is on the other A hole with a small diameter (50μm) is placed in the partition between the tow halves of the cell Ohmmeter measure the change on the resistance when the blood cell pass the aperture

Blood cell sensing

Coulter Counter Constant current source (CCS) and voltage amplifier replace the ohmmeter RA is the resistance of the aperture and will be either high or low, depending on whether or not the blood cell is inside the aperture. Amplifier convert the current pulse to voltage pulse

Schematic

Flow cytometry cell counters optical flow cytometry sensing The optical cytometry sensor consists of a quartz sensing sheath designed with a hydrodynamic focusing region cell path region that passes only a single cell at time. Focusing is done by decreasing the diameter of the aperture. Light source is (He-Ne) Laser

Flow cytometry cell counters optical flow cytometry sensing Two Photodetectors (photosensors) Photodetector A detects forward scatted light Photodetector B detects orthogonal scatted light blood sample enters the analyzer Optical counter → WBC count Colorimeter → hemoglobin Optical flow sensor → RBC count

Schematic