| Determining prothombin levels is necessary to plan or evaluate anticoagulant therapy, to diagnose various inherited conditions, such as hyperhomocystinemia, elevated factor VIII levels, dysfibrinogenemia, factor XII deficiency and disorders of plasmin generation, and to assess acquired conditions, such as pregnancy, postoperative state, antiphospholipid syndrome, hyperhomocystinemia, among others. Prothrombin levels are also monitored along with other tests (such as aspirate aminotransferase and alanine aminotransferase) to help evaluate liver function. Given the broad applicability of this test, it is helpful to many clinicians that several point-of-care products are now available for the prompt, accurate determination of prothombin levels.
Prothrombin time (PT) is the sole test used to measure the effectiveness of coumarin-type anticoagulant drugs, such as warfarin sodium (Coumadin). The most common methods to report the PT are the clotting interval (in seconds) and the International Normalized Ratio (INR). Targets for the INR vary, depending on the reason for anticoagulation. For example, a patient having hip surgery, who is being anticoagulated to prevent deep vein thrombosis, may have a target INR of between two and three. To prevent arterial thrombosis in a patient with an artificial heart valve, the INR therapeutic goal may be in the 2.5- to 3.5-range.
Several medical manufacturers have gained CLIA-waived status for their PT test devices, allowing rapid assessment in the point of care setting, and, in the cases of several waived-devices, in the patient’s home as well.
Roche Diagnostics Corporation, Indianapolis, Ind., a division of Swiss F. Hoffmann-La Roche Ltd, produces the CoaguChek® S System, designed for health care professionals to enable on-the-spot analysis of coagulation levels during mobile emergency treatment, in hospital and in general practice. The device employs electromagnetic field kinetics to determine PT. A single drop (10 µl) of capillary or venous whole blood is applied to a test strip containing thromboplastin, initiating the coagulation cascade. Alternating magnetic fields in the cocktail cause pre-incorporated iron particles in the strip’s reaction chamber to move. An endpoint is reached when the formation of a clot causes immobilization of these particles.
The company says that the system includes one of the fastest coagulation meters available, with results available within one minute. The hand-held meter is icon-based, with a large, easily read display. The open sample-application area and flashing light make sample targeting easy. The meter recognizes errors and controls are identified automatically. Automatic internal controls monitor the meter and test strip for accurate function.
International Technidyne Corp., Edison, N.J., manufactures the ProTime® Microcoagulation System, which uses fingerstick whole blood samples and displays test results as INR and PT interval in four to five minutes. It consists of a ProTime instrument, a reagent cuvette and the Tenderlett® Plus incision device. It has also been approved for patient self-testing, and is available by prescription. According to the company, only ProTime runs two levels of quality control with each patient's sample and is the only PT analyzer that automatically runs quality control with every test.
HemoSense, Inc., San Jose, Calif., manufactures the HemoSense INRatio™ meter, which also provides results in PT and INR within two minutes, using fresh capillary whole blood.
The device features automatic self-testing and includes a quality control system. The company reports that the INRatio meter has an easy to use interface to change the time, date and other features, a large screen, storage for up to 60 tests and a built-in communication port.
The three firms reviewed here represent all of the CLIA-waived devices currently in production. The medical device field changes rapidly and previously available products sometimes vanish from the market. This has recently happened with two additional CLIA-waived PT monitors, the Harmony™ INR Monitoring System produced by LifeScan, Inc., and the AvoSure system from Avocet Medical, Inc. (Beckman Coulter, Inc. has acquired the rights to the AvoSure technology).
Despite sudden shifts in some products, the availability and increasing sophistication of point of care diagnostic devices is clearly a permanent and positive development. Use of these products saves time and expense, promotes effective continuity of care and enhances convenience for patients and caregivers alike.
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