Internal normalised ratio (INR) corrects for the variability in prothrombin time (PT) results caused by differing sensitivities of the thromboplastin reagents used during testing
Staff at Kettering General NHS Trust have been evaluating the Hemosense InRatio portable INR analyser, which is exclusively available in the UK and Ireland from Sysmex UK.
For patients on oral anticoagulation therapy such as warfarin, prothrombin time (PT) is the traditional method of determining how well the treatment is working, and regular monitoring is important as part of cardiac risk assessment.
The internal normalised ratio (INR) corrects for the variability in PT results caused by differing sensitivities of the thromboplastin reagents used during testing.
The InRatio PT monitoring system is an in vitro diagnostic system that brings quantitative laboratory-quality results to the point of care environment, and has been in use for the best part of a year by phlebotomists at the Trust's supervised home-testing outreach clinics.
Lightweight and portable, the InRatio has an easy to read screen and reagent strips with internal controls, which means the results cannot be issued unless the controls are within the pre-determined target range, says Sysmex UK.
Each strip has a clearly identifiable batch number and expiry date, which are important for quality control and ensure that any strips with incorrect batch numbers are automatically rejected.
There is no risk of compromising the integrity of other strips when a strip pack is opened as they are supplied individually in sealed pouches, says the company.
It is simple to train staff to operate the InRatio, and it can be used for testing patients who are inappropriate for intravenous sampling, such as IV drug users and patients on haemodialysis.
Consultant haematologist Helen Kelsey commented: "It is extremely reliable for capillary testing at home.
"We have done venous checks and run controls in parallel and are happy that we can trust the InRatio alone".
"I am confident that the reader can measure accurately down to 0.7 (and up to 7.5).
"As a matter of course, if the reading is above 5 or below 1.5, a venous sample is sent for analysis on the laboratory system", said haematology laboratory manager Mike Silverstone.
Care must be taken when planning home testing, as INR testing is complex and there are a number of factors that influence the result.
"Patient self-testing is OK in principle as long as it is used in a controlled manner with the appropriate level of quality control, patients are properly trained and there is regular contact with the clinician" explained Kelsey.
The InRatio is not designed for high throughput testing of patients, but it is said to be ideal for use for outreach testing and controlled patient self-monitoring.
It is important that these methods of testing are linked in to a well-co-ordinated and centralised service framework, as at Kettering NHS Trust where it is working well.
As Silverstone says: "It must be a partnership between the patient, laboratory, and the clinical service".
