Roche CoaguChek XS System User Manual download pdf (Page 24)

Report 06024: CoaguChek XS system

Technical assessment

Instrument reliability

No mechanical failures were encountered during the evaluation. Only two error

messages from 167 tests occurred post-testing i.e. after the code numbers on

the instrument and test-strips were confirmed as matching: one error pertained

to blood application (Error 5) and the other was a measurement error (Error 6).

No quality control errors occurred..

User assessment

As with most point-of-care monitors, the CoaguChek XS only displays the INR

results to one place of decimals, whereas typical laboratory generated INR

values are recorded to two decimal places.

At present, there is no quantitative quality control material available for the

CoaguChek XS. Furthermore, as only fresh whole blood can be used, it is not

possible to test external quality assurance materials. It is recommended that

some form of external quality control as well as external quality assurance are

regularly performed on all point-of-care coagulation monitors (England et al,

1995; Fitzmaurice et al 2005). Consequently, independent quality assurance of

the CoaguChek XS would need to be performed by periodically testing a paired

capillary blood sample on a separate CoaguChek XS (or other point-of-care

monitor) maintained by the practitioner managing the oral anticoagulant care, or

using a paired venous sample tested by a laboratory based coagulometer.

Each code chip provides the instrument with lot specific calibration data and

expiry date. It was observed that a mismatch between the test strip code and

the chip code was possible. If the user places a test strip from a different lot on

the monitor, but then presses the memory button rather than replacing with

tests strips matching that of the current chip an incorrect INR value may result.

The manufacturer’s manual does emphasise the importance of matching test

strips to the current code chips but we feel that this should be further highlighted

in any protocol devised for self-testing with this instrument. Obviously a ‘fail-

safe’ electronic check would be preferable.

Each time the monitor is switched on a full display check appears showing all

symbols that may be displayed. There is a facility to call up the display after

start-up to allow checking against figures in the user manual. The manufacturer

suggests that this should be checked frequently to ensure that reading errors do

not occur.

We felt that the light weight compact size of the instrument were advantageous

when testing on patients: easily portable to where the patient was being finger-

pricked and thus testing could readily be performed in a timely manner with

minimal likelihood of blood spillages.

We also noted the low rate of test-strip failure, minimising the cost of repeat

testing.

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Roche CoaguChek XS System User Manual Page 24