Point-of-care testing (POCT) is all the rage right now, and for good reason. These often portable, easy-to-operate devices and instruments return results quickly, enabling immediate treatment or intervention. POCT also short- circuits many steps involved in lab-based testing, obviating the need to collect a specimen, transport it to the lab, perform testing, and transmit the results back to the provider. This speed and efficiency often greatly improves both patient outcomes and patient satisfaction.
Despite its popularity, however, POCT has downsides, and may not always be the best option. As clinical laboratory professionals know, POCT methodologies often are not as precise and accurate as lab-based methods, and fall short of the sensitivity and specificity associated with laboratory analyzers.
Given these drawbacks, laboratorians and other medical professionals considering POCT need to balance POCT’s rapid turnaround and positive effect on patient care with the more robust results available through lab-based testing. Before taking the POCT plunge they also need to understand how results may differ between lab and POCT instruments.
INR: A Case Study
One example of how this tension plays out is in international normalized ratio (INR) testing. Patients on warfarin (Coumadin) therapy need their INR levels monitored frequently to ensure that their anticoagulant level is appropriate. Too high a level could mean bleeding, too low a level could lead to clotting.
For lab-based testing, an order must be obtained to draw blood, the patient must travel to the draw site, and have blood drawn. The specimen is then sent to the lab and analyzed, after which the result is communicated to the caregiver. In this scenario, despite the laboratory’s attempt to keep the turnaround time as short as possible, sometimes patients don’t find out until the next day that their warfarin dosage needs to be tweaked. The convenience of POCT in this case is clear: with INR test results on the spot when patients are in their doctor’s office, their medication dosage can be adjusted immediately.
While this speedy service is a plus, results from point-of-care (POC) INR analyzers may not track well with those from laboratory analyzers. The correlation may be fairly good at lower INR values, but as values rise, POC and lab analyzers may give different values. Since patients’ INR values should be in the range of 2.0–3.5 (depending on indication), this is problematic.
In our facility we’ve discovered a positive bias of approximately 1.2 between our POC and lab-based analyzers. In addition, for values >3.8 the correlation is more erratic. At one of our Coumadin clinics, an INR value of 3.8 triggers a specimen being sent for lab-based testing. At other Coumadin clinics, a pharmacy-developed algorithm requires confirmatory lab-based testing when POCT results are ≥4.0. Still another site uses 5.0 as the cutoff to perform a lab draw. All of these sites are aware of the poor correlation between POCT and lab values. Patient care issues have led them to establish an algorithm that allows them to accept the higher cutoffs.
Is tPA Appropriate?
We also have had to deal with POCT and lab-based INR variances when it comes to emergency department (ED) stroke protocols. Tissue plasminogen activator (tPA) is contraindicated when patients have warfarin in their systems, so ED staff need to determine quickly whether patients can safely receive tPA. However, not all POC analyzers have Food and Drug Administration (FDA) approval for this indication. For those that do, a value needs to be set that would indicate the patient has taken warfarin and therefore cannot be given tPA. Our facility chose a target value of 1.7 to screen out those patients who have taken Coumadin and cannot be treated safely with tPA.
Shortly after we instituted the protocol, the POC instrument we were using was taken off the market. We then had to choose between using another analyzer that was FDA-cleared to perform INR testing for all indications, or determining whether the lab could meet the ED’s required turnaround time. After a series of meetings, we decided the best option was to station some clinical laboratory assistants in the ED to ensure that stroke patients’ blood specimens were collected, transported to the lab, and processed immediately. This process proved to be successful and we now perform our stroke protocol INR testing in the central lab.
These two examples illustrate the balance that organizations need to strike between POCT and lab-based testing. When hospital departments or clinics request POCT, clinical laboratory professionals need to understand the problem our colleagues are trying to solve. If indeed POCT is the answer, then we have the expertise to decide the best instrument or kit to meet that need.
Collaborating upfront for a clear understanding of patient care issues and anticipated POCT and lab-based performance lessens the risk of disappointment and dissatisfaction when the latest trend turns out to be the wrong choice.
Kathleen David, MT(ASCP), is point-of-care testing manager at TriCore Reference Labs in Albuquerque, New Mexico. Email: [email protected]