PTINR Monitoring

What is Anticoagulation?
Anticoagulation is the name given to therapy designed to stop people developing potentially fatal blood clots. Today, it is usually carried out in one of two ways: Firstly in hospital, where the chosen form of heparin is administered either intravenously or by subcutaneous injection. Secondly, in an outpatient setting, where oral anticoagulants (also known as “blood thinners”) are used for long-term clot prevention; with the length of time people requiring therapy, ranging from as little as 3 months through to a lifelong requirement.

Anticoagulation therapy using Coumarol-based vitamin K antagonists has existed since the early 1950s. Warfarin /Coumadin® are oral anticoagulants that stop the production of Vitamin K in the liver, which in turn, reduces the production of key clotting factors in the blood. To ensure people using these medications stay within the desired therapeutic range, the Prothrombin Time (PT) test was developed. This was further improved in the early 1980s and standardised to the PT/ INR (International Normalised Ratio), which is the test that is carried out on the Smart Strip. Essentially your INR result indicates how much slower your blood is clotting than normal. For an example, an INR result of 2, means your blood is taking twice as long to clot as it usually would if you weren’t taking oral anticoagulation therapy (OAT).

People requiring long-term oral anticoagulation therapy (OAT) tend to fall into three disease broad categories: those with diagnosed atrial fibrillation, those with artificial heart valves and those with a recurrent risk of thrombosis. All groups are required to take blood ‘thinners’ to ensure they minimise the risk of developing potentially life-threatening blood clots. Whilst taking anticoagulant medication is essential, there is a risk that if you take too much of this medication, there is an increased chance of developing equally dangerous life-threatening bleeds. To ensure this doesn’t happen you will be given a target INR value by your doctor/nurse, which is individual to you and dependent on the reason you have been prescribed anticoagulant therapy. As it is difficult to hit an exact target value, you will be given a range which it is best for you to stay within. For example, with a target INR of 2.5 your INR range will be 2.0 – 3.0.

For additional information on how your lifestyle decisions and diet can affect your anticoagulation medication go to the factors affecting INR results support page.

Today PT/ INR testing is usually performed in either a hospital-based clinic or in the GP surgery (Physician’s office), and generally requires a 24-hour wait for your result and any dosage changes. To avoid potentially serious complications such as bleeding or strokes, testing must be performed regularly so dosage adjustments can be made by taking into consideration dietary changes or as a result of other physiological effects.

If you are within your therapeutic range, your dose will not be altered. If the INR value is below your range, the warfarin dose is increased; if the value above your range the dose is decreased. The downsides for you with the common current practice is that, there are often long clinic waiting times, a difficulty in finding parking spaces and long waits for a doctor to look at your results before any dosing changes are advised.

Studies have shown that the more regularly you test your INR, the more time you will spend in the ‘safe’ therapeutic range. Clearly with the existing practice, it is not feasible for more frequent INR testing to be performed for either the patient or the physician.
Below are a graph and table showing the improvement in the time in therapeutic range (TTR) related to testing frequency.

Time in therapeutic

The combination of above data and knowledge that the half-life of Coumadins/ Warfarin are in the region of 1.5 days, indicates that patients INR testing approximately once a week, would spend 85-90% of their time in therapeutic range.

Smart Strip INR Information
  • ‘Chip on a strip’ – each Smart Strip has an embedded memory microchip which allows it to store calibration data, expiry date and lot number.
  • On board QC – each strip has two qualitative controls to monitor the humidity and temperature the strip has been subjected to prior to use. If the strip is compromised it will berejected by the CoagMax®.
  • Low blood volume – the SmartStrip INR uses only 5ul of blood, less than any other coagulation system on the market. This feature allows for the use of significantly less painfullancets than any other point-of-care device.
  • Individually wrapped – each strip is individually wrapped with a smart humidity wafer to keep each strip in perfect condition prior to use.
  • Notch design – the test strip has an alignment notch to ensure efficient use and only a small blood sample requirement.