Of all the available pathology tests that can be undertaken at the point of care, nothing has quite caught on like INR testing. A boon to modern medical care, on-the-spot testing for INR allows immediate clinical decisions to be made about a critical result which directly leads to clinical transparency and improved patient care.
INR testing breakthroughs
In recent years, there have been more breakthroughs in the area of INR testing machines and point-of-care devices. These have enabled clinicians and practitioners to conduct tests on-site, and for people who benefit from regular testing, to conduct self-tests at home. These tests have eliminated the need to wait for lab results.
The microINR analyser provides precise and accurate results that are significantly comparable with a laboratory test using plasma samples.1
Normal PT INR Range
For a person who is not taking anticoagulation medication a normal INR reading would be 1. The higher the INR value, the longer it takes for the blood to clot. Likewise, the lower the reading, the higher the risk of bruising and dangerous bleeding.
The targeted range for a person taking an anticoagulant medication varies. There is no set ideal. The range is determined by the clinician on a patient-to-patient basis. For warfarin, the targeted range is commonly set between 2 and 4.
Frequent tests of prothrombin time (INR) are required when a person begins, finishes, or changes medication and periodic ongoing testing is a typical requirement for those on warfarin. The test is essential because an INR that is too low can cause fatal blood clots and too high a value could lead to internal bleeding. Thus, by monitoring a patients INR doctor’s are able to make appropriate adjustments to the dosage of blood thinning medications.
About INR Testing
PT refers to Prothrombin Time and is a measure of how quickly blood clots. INR stands for International Normalised Ratio, which is the standard unit used to report the PT result.
Blood’s ability to clot is an essential biological process that is needed, for example, for wound healing. However, in some cases, there is a danger that a person could suffer from life-threatening blood clots. Anticoagulant medication is available to these people. PT INR testing is performed to ensure that the PT is within a targeted range set by the clinician.
How to test INR
Traditionally, INR tests have been performed by taking a blood sample and sending it to a lab for analysis. Results would be sent back to the general practitioner, usually within one week.
In recent years, however, there have been significant breakthroughs in the area of INR testing machines and point-of-care devices. These have enabled clinicians and practitioners to conduct tests on-site, or for people who work in conjunction with their GPs, to conduct self-tests at home and enjoy the benefit of regular testing.
Conditions which may require regular PT INR testing
INR tests are important for people using oral anticoagulation therapy, such as warfarin, heparin, coumadin, as well as many other brand names. Warfarin is a life-saving drug, however, it has a narrow therapeutic range and requires regular testing to ensure efficacy.
Medicare for PoC INR tests
While there have been calls from GPs to the House of Representatives Standing Committee to fund point-of-care INR tests, no government rebate has been allocated. However, the purchase of a point-of-care device, such as the microINR does not involve a significant capital outlay when considering the benefits that immediate results deliver.
The relatively inexpensive price of the unit, and the disposable chips, makes it a worthwhile investment for any practice managing patients on Oral Anticoagulant Therapy (OAT) in terms of better patient care, as well as practice efficiency.
Similarly, for patients who travel, are remotely located or wish to work in conjunction with their GP to monitor their INR levels a point of care testing device can be priceless. Some medical insurance companies have been known to provide a rebate to policy holders against the purchase cost of a device, due the the inherit safety benefits of ownership.
The microINR system, which is the latest generation technology, offers free trials to clinicians and trade-ins on older devices, reducing the barrier to adoption.
Benefits of point-of-care INR machines
Research has confirmed that those who require INR testing weekly are 50% more likely to keep within their target range than those who have the INR tested once a month.2,3
This is a significant health benefit for those at an increased risk of developing life-threatening blood clots. It is evidence in itself for those who require regular testing to self-test at home or visit your medical practice for a real-time test.
In terms of ease of use and usefulness, the microINR is a standout diagnostic tool with so many benefits:
- Only a small fingerprick blood 3µL sample is required.
- There are no calibration requirements.
- Devices can store up to 199 results. A built-in USB port enables these results to be transferred.
- Only a small area of bench space is required.
- Quality Control: There are 3 levels of built-in quality control mechanisms.
- Individually wrapped and disposable test chips to ensure minimal waste and contamination.
Everything you ever wanted to know about INR testing machines…
Modern INR analysers are portable and use a lithium battery that can be recharged through the mains, just like a smartphone. Older designs employ disposable AA or AAA batteries for power, generating a need to keep spares on hand or rotate using a charger.
INR analysers measure the time it takes a blood sample to clot (the prothrombin time) by mixing with a thromboplastin reagent, stimulating the clot formation. Whilst the test is conducted in a similar way, the method of detecting the clot varies between devices.
Some detect the end point of the test using electrical conductivity, correlating an increase in resistance with the formation of a clot. Others, such as the microINR, use more novel methods of detection, allowing blood to flow through a serpentine channel and detecting the halt in progress when a clot form using optical detection.
Typically point of care tests for INR are performed using capillary blood obtained by performing a finger prick with a lancing device. The volume of sample required to perform an INR test is usually small ranging from 3 µL – 5 µL and equating to a drop of blood.
For people undergoing regular INR testing this is a clear benefit as the procedure is less invasive and painful when compared to the collection of a whole blood venous sample.
Quailty Control (QC)
If you are unfamiliar with point of care and laboratory testing, in general, the talk of Quality Control can be confusing at first. People often ask us “why do we perform a quality control test”?
Quality control testing is a way of assessing the performance of an instrument and checking that it is operating within expectations. Put another way, regular quality control testing provides a degree of confidence that a result from a device is accurate and can be relied upon clinically.
Quality control testing with PoC INR analysers can be conducted using built-in on-board methods, which are automatic, or external (liquid) material. In both cases, the prothrombin time measured using the QC sample is compared with the known value supplied by the manufacturer to see if they are a good match. Values that differ too greatly indicate a potential systematic issue that should be investigated before further patient testing is conducted.
INR Test Machine Maintenance
The increased availability of INR analysers has been driven by widespread adoption and as a result, devices are now designed to be extremely easy to use and maintain.
Most INR analysers do not contain moving parts so can be expected to have a long operational life with the minimum of ongoing preventative maintenance. The usual requirement is simply to ensure that the device is kept in a clean manner, both to prevent cross-contamination and ensure the longevity.
When Things Go Wrong: Information & Error Codes
Whilst modern point of care INR analysers are designed to be extremely easy to use, sometimes things don’t work out. When such systems identify an issue they will let the user know by displaying a code or message, rather than reporting an erroneous result.
The reason for the problem can be operator error or an issue with the test or device. Usually, the answer lies in the information code. Checking in the back of the operator’s manual usually reveals a table of codes, the related issue and suggested remedial actions.
If you need assistance for your specific device, you should call the manufacturer or supplier and speak with a technical representative who should be an expert in the equipment and be able to assist over the phone.
Factors affecting an INR test result
The result of a PT INR test can be affected by a number of subjective factors. Inconsistencies in diet and lifestyle can impact the result, including drinking in excess of two alcoholic beverages per day.
Thyroid and liver conditions, the use of other drugs, levels of exercise, and herbal remedies, nutritional supplements, and changes in diet can affect the therapeutic activity of oral anticoagulants and INR results.
Diet and vitamin K effects on INR
Vitamin K naturally aids the blood to clot and thereby prevents excessive bleeding. Vitamin K is found in green leafy vegetables such as spinach, broccoli, kale, swiss chard, mustard greens, parsley, and others. Certainly these foods should be eaten and enjoyed, however, it is useful to know that an inconsistently high intake of vitamin K may produce an inconsistent INR test result.
Does red wine affect INR reading?
While taking warfarin or other anticoagulants, it is recommended to limit the amount of alcohol consumed to 1 or 2 drinks per day. Excessive alcohol may slow the effect of warfarin, leading to a build-up of the drug in the body.
- Paniccia R, Priora R, Marcucci R, Mannini L, Poli D, Tafuro EL, Attinasi F, Gori L, Liotta AA and Abbate “Reliability of a new point-of-care portable coagulometer for PTINR test performed in the hospital anticoagulation clinic”, Experimental and Clinical Medicine, University of Florence; Careggi Hospital; University of Florence, Florence, Italy.
- Liska G, Hogan-Schlientz J, Sallee R. Does patient self-test frequency affect oral anticoagulation therapy time in therapeutic range? Presented at the 11th national conference on anticoagulant therapy, 2013.
- Hylek, E. An Analysis of the lowest effective intensity of prophylactic anticoagulation for patients with non-rheumatic atrial fibrillation. N Engl J Med 1996; 335:540-546.