Abbott i-STAT 1, System Manual

Page: 317 / 658

Art: 714382-00D Rev. Date: 02/20/06
20-7
DETERMINATION OF COAGULATION ENDPOINTS
ACT and PT/INR In coagulation tests, the result that is reported is the time required for the
process of coagulation to occur. To determine this time, there must be a
detectable change in a sample parameter correlated to progression of the
process. In traditional coagulation tests, endpoint detection typically relies
on monitoring increases in either blood viscosity or plasma turbidity that
occurs as thrombin converts fibrinogen to clotable fibrin. In an electrogenic
test an electroactive marker that can be detected at either an amperometric or
potentiometric sensor is used to indicate the endpoint. The marker is generated
when a substrate that has been added to the test sample is acted upon by
thrombin. As the coagulation reaction proceeds, the marker concentration
increases, increasing the signal at the sensing electrode. The time required
for generation of the marker correlates to the time required for conversion
of fibrinogen. The coagulation endpoint can, therefore, be determined by
monitoring the marker concentration. Unlike traditional coagulation tests,
electrogenic tests will not be prolonged in samples with abnormally low (less
than 100 mg/dL) fibrinogen levels.
QUALITY CONTROL AND THE I-STAT SYSTEM
Overview Quality control, as a component of an overall quality assurance program,
consists of tests and procedures for monitoring and evaluating the analytical
performance of a measurement system to assure the reliability of patient test
results.
As new technologies evolve, quality control regimens must match the
requirements of the particular analytical system. i-STAT Corporation
recognizes the importance of effective quality control for its analytical
medical devices, and has developed a program that is tailored to the unique
characteristics of the i-STAT System.
The i-STAT System performs blood analysis when a unit-use cartridge filled
with a patient’s sample is inserted into a handheld analyzer or Blood Analysis
Module (as part of the Agilent Viridia Patient Monitoring System).
The measurement methodologies are electrochemical, using microfabricated
sensors housed in each cartridge to measure analyte concentrations directly in
a single whole blood sample (i.e., neither dilution nor reagent mixing steps are
required).
Two characteristics of the i-STAT System, which distinguish it from traditional
laboratory equipment, have significant impact upon the design of the quality
control regimen: its intended user and the unit-use cartridge technology.
As the system is intended to be used by individuals not trained in laboratory
science, the onus is upon the system’s design to ensure that the quality of
results is not dependent upon either user technique, skilled maintenance and
calibration procedures, or the accompanying quality control regimens which
ensure these procedures have been properly performed.
The use of unit-use cartridges frees the i-STAT System from these skilled
maintenance and calibration procedures. It also allows for the design of a
quality control system which automatically monitors those aspects of the