Klinisk Biokemi i Norden Nr 2, vol. 18, 2006 - page 30-31

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Klinisk Biokemi i Norden 31
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Klinisk Biokemi i Norden
(Fortsætter side 32)
In 2005 the Danish manufacturer and supplier
Chempaq AS ordered a SKUP evaluation of the
Chempaq XBC (eXpress Blood Counter) device.
Chempaq XBC is intended for measurement of
Haemoglobin concentration, Leukocyte counts and
three part differential (Lymphocytes, Monocytes and
Granulocytes, concentrations and %) in the primary
health care. Each sample is analysed in a disposable
cassette. Leukocytes, Lymphocytes, Monocytes and
Granulocytes are counted and their sizes are deter-
mined in an impedance cell. Haemoglobin is measu-
red photometrically at two wavelengths. The mea-
suring interval for Leukocytes is 0 – 100 x 109 /L and
for Hgb. 0 – 13 mmol/L (1 mmol/L ~ 1,62 g/dL). The
same type of cassette can be used for both capillary
and venous blood samples.
The Chempaq instrument
The test system comprises of two parts: a small
disposable cassette, the PAQ (Particle Analyzer and
Quantifier), and a Reader. The capillary blood sam-
ple (approx. 20 µL), obtained using a finger stick, is
collected directly in the PAQ, which is then placed
in the Reader. After three minutes, the result of the
test analysis is displayed on the Reader. If the prin-
ter is connected a printout is automatically made.
The Reader includes a docking station (cradle) for
receiving the disposable PAQ.
All blood and reagents are confined within the
PAQ, whereas the necessary electrical and fluid
operations are controlled by the Reader through
connectors in the cradle when the PAQ is inserted.
The fluids in the PAQ are controlled by air pressure
generated in the Reader. The fluid position is moni-
tored by the Reader through optical detectors.
The Reader includes means for collecting the
signals from the PAQ-cell counting sensor and an
optical measurement system for determination of
the haemoglobin content.
All reagents are contained in the PAQ which
means no external handling and storage of reagent
bottles.
Technology
For Leukocytes the measurement principle is the
Coulter principle or impedance cell counting and
sizing. The principle is based on the change in
impedance as cells suspended in a conductive
liquid are aspirated through an aperture, formed in
an electrically isolated membrane. A cell passing
through the aperture will change the impedance and
cause an electric pulse with amplitude proportional
to the cell volume. The size of the change is depen-
dent on cell volume; consequently the cells can be
sub-grouped after size. The Chempaq XBC uses a
cassette in which an aperture is placed. The aper-
ture is produced in a polymer foil by micro laser
technology. Chempaq XBC is designed for analysing
fresh capillary blood direct from skin perforation or
EDTA blood.
The measurement requires 20 µl of blood in
order to fill the capillary tube in the PAQ, of which
volume 3 µl is automatically introduced in the
‘mixing’ chamber by turning a valve when the PAQ
is placed in the instrument. The 3 µl of blood is
mixed with a reagent. The function of the reagent is
1) to hemolyse the erythrocytes, 2) change the oxy-
haemoglobin to a complex of met-haemoglobin
and 3) transform the leukocytes, so the monocytes,
lymphocytes and granulocytes become different in
size. After mixing, the diluted test material passes
the aperture where the cells are counted and classi-
fied after volume. Finally the haemoglobin content
is determined spectrophotometrically in a special
measuring cell. The end point of the reaction is
measured bichromatically at the wavelengths 545
and 880 nm. The second wavelength is used to
compensate for interference that might be caused
by blood components like chylomicrons or leuko-
cytes, or scratches on the surface of the cuvette.
The haemoglobin concentration is calculated auto-
matically and the result is shown on a liquid crystal
display with the other parameters when the PAQ is
removed from the reader. The measuring range is 0
– 13,0 mmol/L (0 – 20,9 g/dL).
The movement of the fluid is controlled by chan-
ging the pressure in the canals and chambers of
the PAQ, while a pair of liquid detectors monitors
the position of the liquid during the procedure. The
results of measurements are shown on the display
of the Reader after 3 minutes and can be printed by
a special printer connected to the instrument.
Blood Cell Counting in the PAQ
The PAQ is the disposable cassette, used for the
blood sample. The same type of cassette is used for
capillary or venous blood samples.
1. The capillary blood sample is collected directly
in the blood inlet placed in the right side of the
PAQ. For a venous sample the blood is simply
transferred to the inlet tray of the PAQ by means
of a disposable pipette.
2. When the PAQ is placed in the Reader the valve is
automatically turned to a vertical position.
3. The reagent from chamber 1 will pass through the
tube into chamber 2 together with the blood sam-
ple (3 µL are used) where it is mixed by stirring.
4. The diluted blood sample is directed through the
aperture and cell counting is started.
5. During filling of chamber 3 the PAQ is calibrated
to perfect the counting.
6. When the liquid reaches the first level sensor (LS
1) the blood cell counting is started.
7. Cell count continues as Haemoglobin chamber
is filled.
8. When the second level sensor (LS 2) is reached
the blood cell counting is completed.
9. Measurement of Haemoglobin is carried out at
two wavelengths (545 and 880 nm) through the
Haemoglobin chamber.
The evaluation was done with capillary and venous
samples from 40 random outpatients, venous sam-
ples from 59 selected outpatients and 43 selected
patients in hospital under standardised conditions
in the hospital laboratory. In addition Chempaq
XBC was evaluated in two primary care centres in
Denmark. Each of them included 40 individuals (40
capillary and 40 venous samples in duplicate).
In a first evaluation in primary care the cassette
lots used were found to produce biased results due
to a technical error that was eliminated in a second
evaluation. The measurement results of the second
SKUP evaluation of the Chempaq XBC
– a new principle for Point Of Care Testing
Esther Jensen, Gunnar Nordin, SKUP
Esther.Jensen@ouh.fyns-amt.dk
Summary of an evaluation organised by SKUP
Report SKUP/2006/47
Chempaq XBC Capillary samples
Venous samples The reader and the PAQ
( Particle Analyzer and Quantifier)
Chamber for
excess sample
Hb chamber
LS 2
LS 1
Chamber 3
Chamber 1
Valve
Blood inlet
Chamber 2
Aperture