2.7. Performance Characteristics
To minimise imprecision the viscometer is calibrated and
quality control checked with standards that are fully traceable
to the British National Physical Laboratory (BNPL),
Teddington, England. The BNPL uncertainty data is available
on request.
Instrument uncertainty is a measurement of its accuracy.
When a patient sample is presented at the test point, the
barcode of the sample will be read by the barcode reader
and the sample will then progress to be tested. If the result of
this sample is outside the preconfigured limits (default 1.4-
2.0 mPa.s) the sample will automatically be retested. If the
result of the second test is within ± 5% of the first test carried
out on the sample, the initial result will be accepted by the
viscometer and is then transmitted (pending approval if set
up for manual sign off). This also ensures viscometer result
repeatability The second result is stored in the viscometer
but marked as void for LIMs and it is not transmitted.
The 1.6mPa.s check control (is measured every ten patient
samples), the control 2.5, control 4.0 and the high and low
calibrator reagents have their plasma viscosity (PV) value
encoded within the barcode on their tubes.
When these reagents are presented to the analyser, their
barcode is read and the reagent is tested. In the case of the
high and low calibrator reagents, this is an optional
functionality and requires configuration.
The result of the reagent test is compared to the value
encoded for that reagent and if it is within ± 5% of that value,
the analysis is accepted.
An uncertainty report for the check and the control 2.5 is
available within the results menu.
In the UK, The National External Quality Assessment Service
(NEQAS) confirms result reproducibility by a monthly
analytical monitoring service producing an independent audit
for all participating laboratories.
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