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Related Books Free with a 30 day trial from Scribd. Related Audiobooks Free with a 30 day trial from Scribd. Gertrude Adu. When a cell passes through this narrow aperture across which a current is flowing, change in electrical resistance i. A small pulse is generated due to a temporary increase in impedance.
This pulse is amplified, measured, and counted. The height of the pulse is proportional to cell volume. The width of the pulse corresponds with the time required for the cell to traverse the aperture.
Cells that do not pass through the center of the aperture generate a distorted pulse that is not representative of the cell volume. Some analyzers use hydrodynamic focusing to force the cells through the central path so that all cells take the same path for volume measurement. An anticoagulated whole blood sample is aspirated into the system, divided into two portions, and mixed with a diluent.
One dilution is passed to the red cell aperture bath for red cell and platelet counting , and the other is delivered to the WBC aperture bath where a reagent is added for lysis of red cells and release hemoglobin; this portion is used for leukocyte counting followed by estimation of hemoglobin. As the stream of hydrodynamically focused cells passes through a beam of light in the sensing zone, the individual blood cells in the stream break the light beam.
Although the sensing zone of the modern light-scatter hematology analyzer employs more than a simple single beam of light, the principle is the same.
Instead of measuring the number of times the light beam is broken by the individual cells in the stream, blood cell counters depend on the amount of light scattered by the passing cells and measure it ahead of the stream.
Scattered light, rather than direct light, provides a better measure of cells because cells of different volume scatter light in proportion to their size. Since each type of cell has a different size and volume, different cells cause light to be scattered at different angles. By measuring the scattered light at different angles, different cells can be counted.
Both are focused on the cell stream in the counting chamber. Optical sensors pick up the scattered light impulses at each angle and count and report the number of each cell type counted. Like other automated hematology analyzers, they also calculate other blood cell parameters based on the cell counts. Some hematology analyzers employ both automated methods in their design in separate analytical channels, with each contributing results to the overall output.
Of the four discreet methods of counting blood cells, automated hematology analyzers utilizing the volumetric impedance principle are the most common, followed by the light-scatter-method. The manual count is the least utilized, but it is useful for counting special cells, and blood smears should still be microscopically examined for parasitic infections and inclusion bodies. However, in some developing nations, manual counts may still be the norm.
For Joint Commission accreditation and College of American Pathologists CAP laboratory certifications, automated hematology analyzers must be included in a hospital's maintenance database. If the maintenance is contracted out, the accreditation authorities still hold the facility accountable for instrument maintenance. If the in-house biomed manager is responsible for all medical device maintenance management, he or she must also maintain the hematology analyzer maintenance records for the two-year retention period dictated by CAP.
If the laboratory is not included in the in-house program, or it maintains separate maintenance records which is often the case , some accommodation must be made locally. If the instrument is maintained in-house, the minimum requirement to provide thorough maintenance services is comprehensive service literature delineating the complete preventive maintenance procedure; both plumbing and circuit descriptions are mandatory.
Under the Clinical Laboratory Improvement Amendments CLIA , most hematology analyzers described in this article fall under the moderately complex regulatory category. Users of equipment in this category are required to have minimal scientific and technical knowledge and training to perform their duties accurately. The test steps are either automatically executed which is the case with most analyzers or easily controlled, and minimal interpretation and technician assessment is required.
These requirements and constraints pertain to operation of the laboratory, testing facilities, and personnel performing the tests. Food and Drug Administration FDA attempt to regulate or establish credentials for individuals maintaining these analyzers. While CAP has maintenance criteria that must be followed to attain certification, neither they nor FDA specifies who will maintain laboratory equipment. Only the Joint Commission, which is not a regulatory agency, addresses maintainer qualifications and credentials.
The risk management issues with hematology analyzers are no greater than with other clinical laboratory equipment. The main risks include inaccurate results, which could result in delay of treatment or inappropriate treatment. The equipment manager should always err on the side of caution when assessing risk.
No electromechanical device operates correctly all of the time. Each design has its advantages and problems. Analyzers based upon or employing volumetric impedance occasionally experience aperture clogging as well as counting errors when the specimen is cloudy. Some samples from patients with uremia, leukemia, and those who are immunosupressed can result in false low WBC counts caused by cell damage occurring in the aperture.
Most sample feed problems can be traced to minute vacuum leaks in the maze of plastic tubing, so it behooves the laboratory technician or biomed to replace tubing at specified intervals as part of scheduled maintenance, regardless of the condition of the tubing.
Light-scattering designs can suffer from misalignment of the laser or light beam, debris in the sample stream, and electronic noise. Furthermore, they tend to record very high cell counts inaccurately. Lastly, using the wrong or expired diluent, flush, etc.
Fortunately, most of these problems are within the purview of the laboratory technician to prevent or correct. The biomed will rarely encounter these problems, but must be aware of them when dealing with inexperienced technicians. Outside of the aforementioned problems, the electronics used in modern hematology analyzers are remarkably stable; trouble-free; and are closely monitored, both operationally and for quality control purposes, by computer software that continually evaluates instrument performance.
Although the lab technician receives extensive training in performing operator maintenance, biomeds may occasionally be required to service hematology analyzers. The failures usually seen by in-house maintainers are hard failures; that is, the permanent failure of a substantial part of the instrument. In these instances, device-specific training is strongly recommended.
Lacking this, knowledge of the test methodology and lab equipment experience coupled with good service literature is the next recommendation; technical phone support from the manufacturer can also be helpful. Even with model-specific training, good service literature is helpful.
Lacking both, the in-house biomed can diagnose and repair most obvious problems like unserviceable power supplies, open and shorted power transistors, burnt out motors, etc. To protect personnel from both HIV and hepatitis, instrument designs are automating the transfer of the blood sample from the collection tube to the instrument.
Modern and future designs automate this process to reduce or eliminate aerosols that may occur when removing the cap of the collection tube. Traditionally, the lab technician removed the cap of the collection tube and either withdrew an aliquot of the sample and injected it into the analyzer or raised the open collection tube up to a sampling tube.
Once inside, the instrument automatically pierces the cap, withdraws the required sample size, and begins the processing.
The Merck Manual of Medical Information: www. Public Law — www. Food and Drug Administration: www. Incremental improvements in both the analysis and control software are regularly fielded by the manufacturer. As more instruments become software controlled, better integration between the various counting methods and systems results in improved histogram and cytogram displays, improved differentiation of WBCs, and higher throughput. Instrument manufacturers are continually working to improve their linearity and expand the reportable ranges.
The next big step is likely to be in the analyzer's ability to perform extended differential counts—the ability to not only identify but to count blast cells, immature granulocytes, and atypical lymphocytes, since those counts must still be performed manually.
An internationally certified biomedical electronics technician, he entered the U. Army in and retired from active duty in Recipient s will receive an email with a link to 'Hematology Analyzers' and will not need an account to access the content. Sign In or Create an Account.
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