CLINICAL LAB SCIENEC

CHAPTER 14: CLINICAL CHEMISTRY 365
Batteries (related groups of tests) may be performed on one type of instrument
and another type of panel or profile (other names for batches or batteries of
tests) on another. Certain tests may be more efficiently performed on one type
of instrument while general testing of broad groups may be more cost effective,
accurate, or give a shorter turnaround time on another type of machine. A great
deal of thought and organization must go into providing the proper instrument
for certain tests, as no one instrument will be the best for all single procedures as
well as for a grouping of procedures related to a given disease state.
There are several terms by which the various automated chemistry instruments
are known. Some instruments are known as single channel and others as
multichannel. The difference between the two lies in the ability of the multichannel
instrument to perform a number of calculations simultaneously. This does
not always mean that one is faster than another in its analysis of samples. Other
types of analytical processes are common. In discrete analysis, each test reaction
takes place in a separate compartment that requires either cleaning or disposal
of an element used in the reaction, before the next procedure begins. Random
access instruments are able to be programmed to accept samples out of order,
even when a large number of tests are already in progress. This is important if
a large batch of routine tests is being performed and a “stat” (immediate need)
request is made by the physician. Sequential analysis means that all tests are
performed in the order they were entered into the analyzer, and batteries of tests
are performed in a certain order.
History of Analyzer Development
The original multiple analyzers developed in the 1950s and 1960s were either
continuous-flow analyzers or used centrifugal analysis to mix the samples and
reagents. The first sequential multiple analyzer instruments were developed by
Technicon. Over a period of a few years, these instruments were improved until
they could perform a larger number of tests in a shorter time. Subsequent chemistry
analyzers employed a range of testing methodologies, using built-in computers
to handle large volumes of data and store patient results and quality
control results.
Micropipettes are also now available to measure very small volumes of
patient samples and dispense them into cuvettes (reaction chambers) through
which spectrophotometers read the reactions. This also nearly eliminates the
problem of carryover (new samples being affected by the remnants of previous
samples and reagents).
Centrifugal analysis used a wheel-shaped device with two ports—one
where the sample, or unknown, was introduced by pipette into a well and
another larger port or well where the reagent was placed. When the “wheel”
was completed with samples and reagent, the instrument spun the samples and
the reagent parcels into the end of the wheel, which was of high-grade, clear
plastic. The reading device or spectrophotometer was able to read the reaction
in the plastic cuvette for each section of the wheel. This system is rarely used
today.
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