CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
physiological functions of cells, tissues, organs, and entire organisms such as the
human body.
Many aspects of early testing procedures to measure constituents of the
blood are still utilized in the modern clinical chemistry laboratory. The original
end-point reaction (also called colorimetric determination), where a reaction
develops to the greatest extent possible, then ceases, is a methodology fashioned
more than a century ago. It is still used but is now performed more effectively
and in a shorter time frame. A second method now determines many enzymes
and even some nonenzymatic analytes (constituents being tested for) by kinetic
reaction, which measures the amount and speed of change occurring in the
reagent and sample mixture over a specific period of time. The end-point reaction
that required perhaps 30 minutes to reach completion can now be determined
by kinetic reaction in only a few seconds. Calculations from basic physics
and chemistry principles are also used to provide test results from processes such
as spectrophotometry (where a reaction is read by the amount of light transmitted
or absorbed in a test reagent) and electrochemistry (chemical reactions that
involve an electron transfer).
In fully automated systems, all the functions and steps are computer driven.
The technician or technologist often has little to do except troubleshoot the functions
of the instrument after all the preliminary information has been entered
and the instrument has been set up to perform a work list of procedures. An
automated system is able to move the provided samples about the instrument
before, during, and after the procedures are completed.
To provide results from a given sample in an automated system, the sample
must first be identified. Following identification, usually from a bar code
affixed at the time the sample is collected, the specimen volume is measured to
ensure a sufficient sample is available for the number of procedures requested.
After making sure there is a sample in the proper position, the system will
begin the actual procedures. Samples sometimes require pretreatment for certain
procedures (this is fully explained in courses dedicated to clinical chemistry).
Reagents and samples will be mixed in the proper proportions and then
subjected to certain conditions that may be necessary for the chemical reaction
to take place. Some of these conditions include acidity, alkalinity, temperature,
and reaction times. The reaction that occurs, for the most part in an instrument
called a spectrophotometer, will then be analyzed, results will be calculated,
and a valid report will be shown on a visible screen. A printed report can be
provided if required. The Laboratory Information System (LIS) is often interfaced
with the chemistry analyzers and results are then automatically transmitted
to the physician’s office or to the area of the hospital where the patient is
hospitalized.
Methods of Analysis
Most larger chemistry laboratories have a number of instruments that are used
for certain groups of tests. When batches of tests are performed only periodically,
there may be an instrument dedicated to only that particular set of tests.
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