An evaluation of a whole blood prothrombin analyzer designed for use by individuals without formal laboratory training.

Background: The prothrombin time (PT) test, which is the most common coagulation test used in the outpatient setting, has not been recommended for office laboratory use because it has been technically difficult to perform. Consequently, serious errors in patient care could occur because of an erroneous result. The Coumatrak (E.I. Du Pont, Wilmington, Del) now allows nontechnically trained office staff to perform PT tests using a fresh capillary whole blood sample, individually packaged reagent cartridges, and a portable battery-operated instrument.

Methods: Coumatrak PT testing was compared with standard methods for both precision and accuracy, using protocols developed by the National Committee for Clinical Laboratory Standards (NCCLS). Reagent stability and operator variability were also studied.

Results: The results produced by a trained technologist and nontechnically trained staff were comparable. Test results obtained with the Coumatrak were approximately 10% higher than results obtained using standard laboratory equipment and methods using comparable blood samples from the same patients. It was found that the capillary blood specimen had to be rapidly transferred to the reagent cartridge in order to avoid factitiously low results.

Conclusions: The Coumatrak can rapidly provide PT test results that are clinically useful for the office management of patients being treated with a warfarin anticoagulant and for the diagnosis of selected disorders. The system was found to be easy to operate, appropriate for use by individuals with little laboratory experience, and was subject to few operational problems during this study.