Point-of-care ACT values not interchangeable between devices
MedWire News: Activated clotting time (ACT) values are not interchangeable across two generations of a point-of-care testing device, US researchers report.
Neeraj Jolly (University of Chicago, Illinois) and colleagues explain that the Hemochron point-of-care system offers two different systems for assessing ACT: the Hemochron Response and the Hemochron Signature Elite. The newer Hemochron Signature Elite system measures ACT based on electronic optical detection of clot formation whereas the Hemochron Response system uses mechanical detection of clot formation.
The researchers performed a prospective observational study to compare ACT values measured simultaneously using the Hemochron Response and Hemochron Signature Elite systems in 126 paired, whole-blood samples obtained from 77 patients undergoing percutaneous coronary intervention (PCI).
The patients had a mean age of 67 years, 49% were women, and 65% of ACT measurements were made after systemic anticoagulation.
As reported in the American Journal of Cardiology the mean Hemochron Signature Elite ACT was significantly higher than the mean Hemochron Response ACT (278 vs 262 seconds) in the therapeutic range of ACT (>200 seconds based on Hemochron Response data).
By contrast, there was no difference in mean ACT between the two systems (157 vs 163 seconds for Hemochron Signature Elite vs Hemochron Response) in the subtherapeutic range of ACT (<200 seconds).
Overall correlation between the two systems was good (r=0.84) but Bland-Altman plots showed that they were nonequivalent. Indeed, the Hemochron Signature Elite ACT values were lower than Hemochron Response values in the lower therapeutic range of ACT (200-250 seconds), whereas in the higher therapeutic range of ACT (>250 seconds) the reverse was true.
The researchers also note that 33% of total samples had more than 10% disagreement between the systems and 8% of samples had more than 20% disagreement.
They suggest that the disagreement between the two systems may be due to the difference in the technique and the underlying method used. "Unlike the Hemochron Response ACT system, which uses 2 ml of a whole-blood sample in a Celite-containing glass tube, the Hemochron Signature Elite system uses only 0.015 ml in a test cartridge."
Jolly and team add that their findings "have important clinical implications" because maintaining adequate anticoagulation during PCI is important to prevent clot formation on intracoronary guidewires and catheters.
They therefore discourage the use of the same therapeutic ACT range for both Hemochron systems as it could result in underdosing of unfractionated heparin, especially in the higher therapeutic ACT range.
"Institutions using these two devices should be cognizant of this difference for ensuring patient safety," Jolly and co-authors conclude.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012
By Laura Cowen