Prothrombin Time - Near-patient Testing

Near-patient Testing

In addition to the laboratory method outlined above, near-patient testing (NPT) or home INR monitoring is becoming increasingly common in some countries. In the United Kingdom, for example, near-patient testing is used both by patients at home, and by some anticoagulation clinics (often hospital-based) as a fast and convenient alternative to the lab method. After a period of doubt about the accuracy of NPT results, a new generation of machines and reagents seems to be gaining acceptance for its ability to deliver results close in accuracy to those of the lab.

In a typical NPT setup a small table-top device is used. A drop of capillary blood is obtained with an automated finger-prick, which is almost painless. This drop is placed on a disposable test strip with which the machine has been prepared. The resulting INR comes up on the display a few seconds later. A similar form of testing is used by people with diabetes for monitoring blood sugar levels, which is easily taught and routinely practiced.

Local policy determines whether the patient or a coagulation specialist (pharmacist, nurse, general practitioner or hospital doctor) interprets the result and determines the dose of medication. In Germany, patients may adjust the medication dose themselves, while in the UK and the USA this remains in the hands of a health care professional.

A significant advantage of home testing is the evidence that patient self-testing with medical support and patient self-management (where patients adjust their own anticoagulant dose) improves anticoagulant control. A meta analysis which reviewed 14 trials showed that home testing led to a reduced incidence of complications (bleeding and thrombosis) and improved the time in the therapeutic range, which is an indirect measure of anticoagulant control.

Other advantages of the NPT approach are that it is fast and convenient, usually less painful, and offers, in home use, the ability for patients to measure their own INRs when required. Among its problems are that quite a steady hand is needed to deliver the blood to the exact spot, that some patients find the finger-pricking difficult, and that the cost of the test strips must also be taken into account. In the UK these are available on prescription so that elderly and unwaged people will not pay for them and others will pay only a standard prescription charge, which at the moment represents only about 20% of the retail price of the strips. In the USA, NPT in the home is currently reimbursed by Medicare for patients with mechanical heart valves, while private insurers may cover for other indications.Medicare is now covering home testing for patients with chronic atrial fibrillation. Home testing requires a doctor's prescription.

There is some evidence to suggest that NPT may be less accurate for certain patients, for example those who have the lupus anticoagulant.