Lay Summary: Home Prothrombin testing is becoming standard in many countries, but it is only now appearing in the USA. The literature shows that it is a reliable way of monitoring Coumadin therpay.
Near-patient testing (NPT) 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 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; for example the Roche Coagucheck® S, or the more recently (2005) introduced HemoSense INRatio®. A drop of capillary blood is obtained with an automated finger-#####, 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. Similar testing methods are used by diabetics on insulin, and are easily taught and practiced.
Local policy determines whether the patient or a coagulation specialist (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.
The advantages of the NPT approach are obvious: 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-######## 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.
Patients on Warfarin usually require monitoring at least once a week.INR is measured daily or every second day during the first week of treatment, with the dose of warfarin (taken in the evening) titrated against the morning’s INR. It is then measured at increasing intervals depending on response. Many patients, once the dose is stable, can be well controlled with 4-6-weekly testing and dose adjustment, but others need more frequent assessment. The guideline with Ansell as first author says: “The most frequent testing frequency is weekly but lower frequency of testing can be justified based on institutional or patient conditions.”
There is some evidence to suggest that NPT may be less accurate for certain patients, for example those who have the lupus anticoagulant.
In addition, in a recent study, the researchers compared weekly patient self-testing (PST), using an interactive voice-response reporting system and Web-based local monitoring, and currently recommended practice: high-quality anticoagulation management (HQACM), with testing carried out monthly at a clinic. The primary end point was an aggregate of stroke, major bleeds, and death. Over an average of 54 months and 8370 patient-years of follow-up, there were 544 primary end-point events—237 deaths, 263 major bleeds, and 44 strokes—but there was no statistical difference in the number of events between the intervention groups. When they looked at total events, not just first events, between the two groups, there was a consistent trend toward benefit for PST on all three components of the primary end point, but none of the trends reached statistical significance. These results of The Home INR Study (THINRS) were presented at the American Heart Association 2008 Scientific Sessions.
Gardiner C, Williams K, Mackie IJ, et al. Patient self-testing is a reliable and acceptable alternative to laboratory INR monitoring. Br J Haematol. 2005;128(2):242-247.
Ansell J, Jacobson A, Levy J, Völler H, Hasenkam JM (March 2005). “Guidelines for implementation of patient self-testing and patient self-management of oral anticoagulation. International consensus guidelines prepared by International Self-Monitoring Association for Oral Anticoagulation”. Int. J. Cardiol. 99 (1): 37–45
- Fitzmaurice DA. Oral anticoagulation control: The European perspective. J Thromb Thrombolysis. 2006;21(1):95-100.
- Brown A, Wells P, Jaffey J, et al. Point-of-care monitoring devices for long-term oral anticoagulation therapy: Clinical and cost effectiveness. Technology Report No. 72. Ottawa, ON: Canadian Agency for Drugs and Technologies in Health (CADTH); February 2007. Available at: http://www.cadth.ca/index.php/en/hta/reports-publications/search/publication/679