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Automated
Analyser
An automated analyser is a
laboratory machine designed to process a
number of samples quickly, with minimal human assistance.
Different methods of putting samples through
have been invented, but usually involve placing
test tubes of sample into racks, which can
be moved along a track, or circular carousels that rotate to make the sample
available. To protect the health and saftey of laboratory staff many
analysers feature closed tube sampling to prevent workers from direct
exposure to samples.
Samples can be processed in batches, or
continuously.
Routine Biochemistry
Analysers
These are machines that process the bulk of
the samples going into a
hospital or private
medical laboratory. And the results should
be out as quickly as possible. There will often be a method that can get
urgent specimens moved more quickly through.
The types of tests required are often
enzyme levels (such as many of the
liver function tests), ion levels (e.g.
sodium and
potassium), and other tell-tale chemicals
(such as
albumin or
creatinine).
Simple ions are done with
ion selective electrodes, that let one type
of ion through, and measure
voltage differences. Enzymes are measured
by the rate they change one coloured substance to another; the results for
enzymes are given as an activity, not a concentration of enzyme. Other tests
use colorimetric changes to determine the concentration.
Turbidity (as created when an
antibody reacts with a test compound) can
also be measured with these machines.
Examples of these types of machines are:
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Hitachi 917
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Hitachi 912
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Abbott Aeroset
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Dade Dimension
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Beckman-Coulter LX
Immuno-based Analysers
Because many substances (such as
hormones or
drugs) have no colour, and cannot cause
another substance to change colour, antibodies must be used to detect them.
The concentration of these compounds is often
too low to cause a measurable increase in
turbidity when bound to antibody, so other,
more specialised, methods must be used.
Examples of these analysers include:
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Abbott Axsym
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Elecsys
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ACS-180
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Abbott TDx
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Abbott Architect
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Beckman-Coulter Access
Haematology Analysers
These are used to perform
full blood counts,
erythrocyte sedimentation rates (ESRs) or
coagulation tests.
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Cell Counters
Cell counting machines sample the
blood, and analyse its cell populations using both electrical and
optical techniques. Electrical analysis involves passing a dilute
solution of the blood through an aperture across which an electrical
current is flowing. The passage of cells through the current changes
the
impedance between the terminals
(the Coulter principle}. A lytic
reagent is added to the blood solution to selectively burst the red
cells, leaving only white cells and platelets intact, then the
solution is passed through a second detector. This allows the a
differential count of RBCs against WBCs and platelets to be
obtained. The Platelet count is easily separated from the WBC count
by the smaller impedance spikes they produce in the detector due to
their small volume.
Optical detection is utilised to gain
a differential count of the populations of white cell types. A
dilute suspension of cells is passed through a flow cell, which
passes cells one at a time through a capillary tube past a
LASER beam. The reflectance,
transmission and scattering of light from each cell is analysed by
sophisticated software giving a numerical representation of the
likely overall destibution of cell populations.
Reticulocyte
counts can be performed by many analysers, but are just as often
carried out manually by staining blood in a Merrett tube and
performing a cell count under the microscope. Some analysers have a
modular slide maker which is able to both produce a blood film of
consistent quality and stain the film.
Examples of full blood count machines
are:
Coagulometers
Automated coagulation machines or
Coagulometers measure the ability of blood to clot by performing
several types of tests including clotting
screens,
INRs, lupus anticoagulant screens
and factor assays.
Coagulometers require blood camples
that have been taken in tubes containing trisodium citrate as an
anticoagulant. These are used rather than
EDTA anticoagulated tubes as the
mechanism behind the anticoagulant effect is reversible by the
addition of calcium ions to the solution. Depending on the test
different substances can be added to the blood plasma to trigger a
clotting reaction. The progress of clotting is measured optically by
measuring the absorbance of a particular wavelength of light by the
sample and how it changes over time.
Coagulation machines include:
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Sysmex CA-1500
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Biomerieux MDA
Other Haematology Apparatus
Automatic ESR readers, while not
strictly analysers, hold a rack of samples for an hour, then after
an hour determine how far the
red cells have fallen, by detecting
levels with light beams.
As ESR tests become less popular they
are being replaced by Plasma Viscosity
tests. The advantage of this test over ESR is that less variables
can affect the result so it can give a more direct impression of the
plasma protein content of a sample. The analysers commonly work by
drawing a small sample of plasma through a narrow capillary using a
constant pressure and measuring the time taken for the sample to
move a known distance.
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