Laboratories are under a lot of pressure these days, as they are asked to do more work with fewer resources. The problem is further compounded as experienced laboratorians are retiring, taking with them years of valuable experience running and interpreting traditional microbiological techniques. These trends, along with remaining lab professionals being stretched by continual cost-cutting measures, make the laboratory environment increasingly stressful and have helped fuel the demand for better diagnostics to help uncover the etiological agents behind patient illnesses.
When making the decision to bring on a new test, a laboratory director has many choices. Two key criteria are performance and price. The primary imperative for a lab is accurate reporting for doctors. Therefore, sensitivity, specificity, and predictive value assay numbers are critical factors in the decision-making. The lab doesn’t often get accolades for being right, but it certainly hears about it when it is wrong. The problem is that performance and price don’t always correlate with the timing necessary to impact patient treatment decisions.
Despite all the inspections and paperwork required by laboratories, performance is limited by the condition of the clinical samples received. In the case of influenza, we know that the viral titers are highest in the earliest phase of disease. When a patient comes to a hospital cannot be controlled, but if arrival is five days or more after symptoms and the lab has a validated rapid assay as its front-line defense, the sensitivity will be so poor that a test is hardly worth performing. If sample collection is poor, the performance of any influenza test, even by the best of laboratories, will suffer.
These issues have led many hospitals to disregard rapid influenza tests in favor of molecular options. The literature on these assays has been uniformly positive on a performance level, most often surpassing the gold standard of viral culture. The problem has not been the numbers reported from the laboratory, but rather the time it takes to get results.
Influenza is highly contagious, so the last thing a hospital wants is for infectious people to linger in waiting rooms, risking further infection of other patients and medical staff. Patient satisfaction is closely tied to wait times in the emergency department. Patients want to be in the emergency department for as little time as possible and leave with a prescription. If laboratories have the best performing tests available but don’t meet the timeline necessary to impact patient care, testing might not be worthwhile.
Meanwhile, rapid influenza tests satisfy the desire for fast turnaround time and most have good specificity, so positive results don’t have to be backed up. However, the sensitivity is lacking and can drop significantly if tests are not evaluated on the right patient population with a proper sample.
New molecular technologies are starting to bridge the gap between accuracy and speed. One reason that molecular methods have historically taken so long is that the clinical sample has to be elevated to a high temperature to denature the DNA, then reduced to a lower temperature to anneal primers, and then finally raised to a mid-temperature to elongate the strands. Each change in temperature and cycle takes additional time. Meanwhile, organisms in nature do not need to change in temperature to make new DNA. There are some bacteria that can complete an entire genome and divide in the space of 20 minutes. Even human cells replicate DNA at the single temperature of 98.6°F.
Isothermal molecular tests are able to reduce the time of traditional PCR assays by eliminating heating and cooling. With nicking enzyme amplification reaction (NEAR) technology, the influenza virus, for example, is lysed, exposing the viral RNA. Reverse transcriptase converts the RNA into DNA. A nicking enzyme subsequently binds to target sequences and cleaves a single strand of the duplex. DNA polymerase is able to initiate the extension. The nicking enzyme can then nick at the two sites in the amplification duplex, continually creating new strands. Detection is by a fluorescently-labeled molecular beacon. Fluorescence is released as the fluorophore and quencher are separated when the beacon stem is opened. A small instrument can capture this fluorescence.
With these new technologies, we are seeing the ability to deliver results in the same time as traditional lateral flow rapid assays and with increased performance. One other benefit is that these reactions are contained, reducing concerns over amplicon contamination. Ease of use is also important. Manufacturers are striving to have the newer technologies CLIA-waived, which will free up experienced laboratorians to work on more complex assays.
A negative to these assays is additional cost per test. Laboratory directors are forced to review their budgets for cost savings. During the height of the novel H1N1 pandemic, many laboratories stopped influenza testing, as rapid tests could not achieve desired performance levels and molecular assays added financial burden without increasing the efficacy of patient outcomes. As these new assays become available, laboratories need to consider the overall savings per influenza event. One study showed that a positive influenza test was able to lead to cost savings by reducing the number of chest x-rays and antibiotic prescriptions. A reduction in antibiotics helps lessen the overall global health threat of antibiotic resistance and helps patients with potential complications such as acquired C. difficile.
Healthcare is in a state of flux, and no one knows exactly what its systems will look like in the future. There is greater focus on driving better patient outcomes with, unfortunately, fewer financial resources. Newer tests can help fill this gap. However, a strong caution must be given that newer technologies are only a part of the solution. There still needs to be strong focus on training medical staff and laboratory professionals to take the right samples from the right populations. Molecular tests may be able to overcome poor sample collection better than a rapid test, but they cannot completely resolve the problem. In the case of influenza, doctors must understand that ordering influenza in the summer when there is no circulating flu is a waste of money, and, even with the best test, will not have a good positive predictive value. Finally, actionable test results need to be recognized so therapy can be optimized for better clinical outcomes and cost-effectiveness.
Norman Moore, PhD, serves as Director of Scientific Affairs, Infectious Diseases, for Alere, Inc. K.C. McGrath serves as Respiratory Product Manager for Alere, Inc.
