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PT/INR on an i-STAT

From Pearl Gabrielle:

Hi, Our ED  wants to add PT/INR to their i-STAT. I am not a fan of coagulation point of care (POC) testing and am looking for information or studies done comparing the i-STAT to coagulation analyzers, specifically Stago analyzers.

Hello, Ms. Gabrielle, and thank you for your question. There is a large volume of literature that correlates POC instruments to central laboratory plasma-based PT/INR testing. I’ll start with Abbott’s own package insert for their Prothrombin Time PC/INR cartridge. Their data are encouraging, with CVs of less than 5%. They performed correlations with an STA Compact®, but using Dade Innovin® reagent, the r value was 0.943,  acceptable.

Most literature compares plasma-based coagulation to whole blood PT/INR results from the Roche Coag-U-Chek®, which probably occupies a larger market share than the i-Stat. One example is Toulon P, Ozier Y, Ankri A, et al. Point-of-care versus central laboratory coagulation testing during haemorrhagic surgery. A multicenter study. Thromb Haemost 2009;101:394-401. These studies reflect CVs and correlations equivalent to the data published in the package insert.

Anticoagulation clinics prefer POC testing because the patient need not wait the usual 45 minutes for a conventional specimen to be delivered to the lab, centrifuged, analyzed, and reported. EDs may be less inclined to use POC for this purpose, as they may not require a rapid turn-around time. Many EDs, however, already have i-Stats for other purposes such as electrolytes, glucose, or cardiac markers. The down side of POC testing is that the CVs are usually a little larger than plasma-based PT/INR, and there is an automatic multiplier factor added in POC circuitry that converts a whole blood PT to an equivalent plasma PT. However, studies that compare the percentage of time the patient spends within the INR therapeutic range consistently show more desirable data when using self-administered PT testing with a portable POC device compared to using a central laboratory.

Finally, you may wish to obtain a copy of Van Cott EM. Point-of-care testing in coagulation. Clin Lab Med 2009 ;29:543-53. This article appears in an entire issue devoted to point-of-care testing and could give you the answers you are looking for.

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