Use of Near Patient/Point of Care INR Testing. The provider should use Near Patient testing methods as appropriate to deliver the service. The results should be available to patients in the majority of cases within the same appointment, for example unless further advice is required from the lead clinician to determine the most appropriate course of treatment. A protocol for the use of near patient testing should be used by staff delivering the service. All members of staff involved in using near patient testing methods should be trained in the use of the equipment and a training log kept. Providers must follow the equipment manufacturers quality control procedures. Limitations of point of care testing (2) Providers must ensure they check the test strip inserts for any updated guidance on testing. The provider should be aware that some INR monitors may be sensitive to the presence of low molecular and unfractionated heparin. The manufacturer’s instructions for use will state whether the test strips/cuvettes contain a heparin inhibitor and the maximum allowable concentration of heparin with which the monitor may safely be used. Caution should be used when point of care test monitors are used to test INR in patients receiving heparin therapy or who may have contamination from indwelling lines. Like all clotting tests, INR tests may suffer from interference by ‘lupus anticoagulants’ (LA). These are the antibodies found in the plasma of patients with antiphospholipid syndrome, which prolong in vitro clotting tests. The effect of LA is variable and unpredictable. Consequently, it is necessary to check for LA interference in patients with known antiphospholipid syndrome and some of the patients may not be suitable for point of care INR testing. Patients may have unknown clotting defects, which may affect the point of care INR result. If a patient gives repeated erratic results, it may be necessary to send samples for laboratory analysis. As the amount of plasma in whole blood varies with the haematocrit (packed cell volume), anaemia and polycythaemia may cause erroneous INR results. The instructions for use state the range of haematocrit values which the point of care device may safely be used. Point of care monitors which use optical clot detection methods may be affected by high levels of bilirubin (jaundice) or triglycerides. The instructions for use will state if these substances interfere with testing and will give maximum safe levels.
