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Abbott's iStat Comes Out on Top in Study Comparing Blood Clot Monitoring Tests

NEW YORK (360Dx) – Clinicians at Medical College of Georgia in Augusta have conducted a head-to-head comparison of instruments and tests used to monitor blood clotting during medical and surgical procedures, concluding that the Abbott iStat point-of-care analyzer performed the best.

The investigators published the results of their study recently in the journal Lab Medicine.

"This was a comparison of the different instruments available, and we're indicating that one instrument is better than the others without having a vested interest in any of them," Gurmukh Singh, chief of clinical pathology at the Medical College of Georgia and the study's senior author, said in an interview.

Overall, the assessment was part of a quality management program in which the investigators evaluate analyzers on an ongoing basis to ascertain whether they meet patients’ needs, he said.

During procedures such as open-heart surgery, cardiothoracic surgery, or inserting stents to improve blood flow in the heart, patients are given anticoagulants to prevent blood clots from forming, and the patients require bedside monitoring to make sure the drugs aren't causing problems such as excessive bleeding.

Fast-acting heparin is frequently administered as an anticoagulant, and clinicians usually use a measurement of activated clotting time to monitor the effectiveness of their treatments.

In parallel testing of instruments at Medical College of Georgia, the investigators compared the iStat with other instruments, including the Accriva Hemochron Signature Elite ACT+ and Hemochron Response analyzer produced by Instrumentation Laboratory, a Werfen company, and the Medtronic Hepcon Hemostasis Management System. None of the instrument manufacturers responded to requests for comment on the study results.

"A number of instruments are available that you can use at the patient's bedside to monitor heparin treatment," Singh said. "Our investigation was triggered by external proficiency testing done by the College of American Pathologists, which revealed that results from the Hemochron instrument could be unreliable."

In all, the investigators analyzed the performance and cost of five tests available for the monitoring of heparin-induced anticoagulation. Among them, the three most commonly used are assays for activated partial thomboplastin (aPTT) time, anti-Xa, and activated clotting time (ACT).

An aPTT assay monitors clot formation by measuring the absorbance of light passed through a specimen. As fibrin strands form, the absorbance increases, and less light is perceived by the detector. An anti-Xa assay directly measures heparin level by detecting a color change using a chromogenic substrate that binds to free heparin.

Activated clotting time, which can be measured by a variety of point-of-care platforms, has an advantage over the other two methods in that it enables use of whole blood without requiring that citrated plasma be drawn off after centrifugation, the investigators said.

Point-of-care activated clotting time measurements also provide advantages over laboratory-based tests for these applications, Singh said. Benefits include shorter time between gathering specimens and receiving results, use of specimens with less volume, and a reduction in mishandling and mislabeling of specimens.

The researchers noted that the Accriva Hemochron Signature Elite ACT+ and Hemochron Response are widely available ACT monitoring systems.

The Signature Elite ACT+ platform measures clot formation by detecting the impedance of flow between two optical sensors. The Hemochron Response platform detects clot formation by the disruption of a magnet at the base of the test tube when a clot is formed.

Medtronic's Hepcon Hemostasis Management System (HMS) Plus uses a microprocessor-based multichannel cartridge to quantitatively determine the heparin concentration of whole blood via the principle of heparin/protamine titration. It provides an ACT measurement by an indirect, mechanical measurement of photooptic impedance of a plunger, which slows during clot formation.

By providing POC heparin concentration and ACT values, the Hepcon platform may represent an overall index of anticoagulation, but it requires an accurate estimation of blood volume, the researchers said. They also noted that the Hepcon platform requires a large specimen volume per test, has the largest upfront cost investment per instrument, and occupies the largest amount of space among the POC platforms.

The Abbott iStat platform uses fresh blood mixed with diatomaceous earth, a particulate clotting activator, and a thrombin substrate. The platform measures the electroactive interaction of diatomaceous earth with thrombin, which is representative of the thrombin-cleaved amide linkage observed with fibrinogen, and this interaction can be measured amperometrically.

The researchers noted that the iStat instruments are less affected by temperature, dilution, fibrinogen levels, and user technique, and require lower quantities of liquid for quality control.

Singh said that during testing, the correlation coefficient — a calculation of the similarity of results between two matching analyzers from the same company measuring the same sample — was less than .70 for the Hemochron analyzer while the investigators were looking for a correlation value greater than .85.

In their investigation of the iStat platform, the investigators found that two iStat analyzers had a correlation coefficient of .97, well above the required threshold, Singh said.

The hospital had already been using the iStat to conduct testing at patients' bedsides, doing clinical chemistry testing for parameters such as sodium, potassium, lactate, and others. In general, clinicians in the medical college use the platform to diagnose and monitor critically ill patients, most frequently in emergency and operating rooms so that people can get a quick turnaround on their test results, Singh said.

In operation, the handheld iStat instrument provides results in minutes that can be seen at the bedside and by a medical director through a wireless link, he added.

The implementation of the iStat for the monitoring of blood clotting was previously reported by clinicians at the Thomas Jefferson University Hospitals in Philadelphia, Pennsylvania. As a result of a comparison between the iStat and the Hemochron Signature Elite, the clinicians there also opted to use the Abbott instrument instead of the Hemochron system in the operating room.

However, the monitoring of blood clotting and other applications using the iStat are among a few exceptions where it makes sense to opt for point-of-care testing over laboratory testing, Singh noted, adding that the Medical College hospital performs 2.5 million tests each year in its main laboratory.