The simplest counters determine the count of the blood cells (erythrocytes, leukocytes, thrombocytes), hematocrit, and the concentration of hemoglobin.
More advanced electronic counters can, in addition to the cell count, hematocrit and hemoglobin, calculate erythrocyte indices, graphically present the curves of the cells distribution by volume, and determine the type of leukocytes, etc. Some electronic counters can provide up to 28 various parameters.
The principle of their work is the same in the simplest and most complicated counters. They work on the principle of impedance (e.g., Coulter, Celloscope), or optical methods (e.g., Technicon, Sysmex).
Nowadays, individual leukocyte populations can also be differentiated on such counters (measurement of peroxidase activity, repeated measurement by a direct current, measurement of impedance by using alternating current, laser light scatter method, specific chemical lysis of subclassifying leukocytes, and laser light depolarization on eosinophil granules).
All counters give good results if the blood picture is normal; if the blood picture is pathological, there are specific limitations when thrombocytes are low or very high (> 1 million/µl), when leukocytes are high (>100000/µl), and in case of immature cells. In these cases it is necessary to check the result under the microscope.
Although some clinically important blood properties can be measured by chemical or physical means, hematologic evaluation almost always requires enumeration of the blood elements and determination of the morphology of each type. These examinations can be done by manual methods, but this approach is time-consuming, tedious, and inaccurate. Electronic methods have been developed in order to provide analysis of blood with, in most instances, significantly less error. |
