Not long ago, “Contagion” acquainted the movie-going public with a fictional pandemic that federal health authorities deemed entirely plausible. Missing from the action, however, was a tool being refined to solve such microbial mysteries: point-of-care testing.
Much of the movie's plot unwinds in the wintry Midwest, where the medical team seems to have no way of culling folk with seasonal flu from the growing throng of those suffering the new pathogen, which started out in Asia in a pork dish before literally going viral, thanks in large part to being dined on by a visiting American. Perhaps it is not all that surprising, though, that none of the doctors whipped out a pocket-sized test device. Rapid tests detect influenza, but they would threaten to slow down life-saving efforts. After all, they reportedly have less-than-optimal sensitivity, yielding results that may require more follow-up testing.
That view is actually changing, right along with the widening applicability of these technologies. To find out if an emergency department can essentially go lab-less for some patients with point-of-care technology, Danish scientists conducted a randomized trial to see if there was a time differential — a significant one — when point-of-care is compared with standard laboratory service. In the Denmark ED, point-of-care devices are used routinely to measure blood gases, glucose, electrolytes, and hemostasis, but the researchers wanted to know if newer technology and targeted use could cut time to action. It turns out that the difference by point-of-care testing was negligible for cases of suspected deep venous thrombosis, acute coronary syndromes, and appendicitis. But use of point-of-care testing to detect bacterial infections was a different story. Time to clinical decision-making was reduced significantly, from about seven and a half hours to four and a half hours. (Scand J Trauma Resusc EmergMed 2011;19:40.)
The U.S. Department of Health and Human Services now regards future use of rapid diagnostics a much-needed countermeasure for potential flu pandemics, and the Centers for Disease Control and Prevention has issued guidelines for their use. (See FastLinks.)
Already, these advances are finding a medical home. At the Medical College of Wisconsin, common flu viruses are being differentiated by use of nano-particle probes on respiratory specimens. (J Clin Microbiol 2010;48:3997.) “We are using this real-time approach, and have been for some time. It is part of our protocol,” said Nathan Ledeboer, PhD, an assistant professor of pathology at the college and an author of the study.
But Carl Schultz, MD, the director of research at the Center for Disaster Medical Sciences at the University of California, Irvine, said another question should be asked: Even if the testing is quick and reliable, does it change outcome? In fact, he makes the same point as many of his colleagues did in a recent survey. Emergency personnel indicate these tests should be accurate, highly portable, easy to handle, and if utilized in epidemics, capable of detecting multiple pathogens in a single test. (Point Care 2010;9:65.) In sum, patient care should benefit, Dr. Schultz said.
“I do think it'll be five to 10 years before point-of-care molecular tests become widely available,” said Sheldon Campbell, MD, PhD, an associate professor of laboratory medicine at Yale University School of Medicine in West Haven, CT. “We need at least a generation of simplification and automation before the current molecular tests will really be suitable for point-of-care use.”
Distinguishing between a potentially emerging infection — such as the infective agent possibly involved in a pandemic — and a less life-threatening one, such as seasonal flu, “would be helpful because then one could rapidly triage patients to separate the less serious from the infected and facilitate appropriate allocation of limited medical resources to the critically ill,” observed Nam Tran, PhD, an associate-director of the Point-of-Care Technologies Center at the University of California, Davis.
Now some studies are showing that these rapid imaging tests can be done on patient groups once excluded. (See sidebar.) Nowhere has this been more evident than with portable ultrasound. In one recent case report, a cervical ectopic pregnancy was diagnosed in the ED at North Shore University Hospital in Manhasset, NY. (J Emerg Med 2011 Aug 3. [Epub ahead of print].) In another, a cornual ectopic pregnancy was detected in the ED of Massachusetts General Hospital in Boston. (J Emerg Med 2011;40:e81.) And, when point-of-care ultrasound was used for pre-intubation scans prior to laryngoscopy at the University of Arizona Health Sciences Center in Tucson, difficult cases were determined by visualizing the soft tissue thickness around airways. (Acad Emerg Med 2011;18:754.) Further investigations by the same team will aim to establish if this seems to reduce morbidity — and time.
The point-of-care single-panel cardiology screen is being put to the test, too. At the University of Sheffield's School of Health and Related Research, investigators evaluated the clinical efficacy and cost-effectiveness of just such a panel for chest pain patients suspected of myocardial infarction. Compared with control groups, the proportion of patients discharged home from the ED increased substantially after these quick results, even though the cost of the patient visits wasn't reduced overall. (Health-Technol Assess 2011;15:1.) Is this savings in time seen as cost-effective? Not by the researchers in Great Britain, because the testing actually led to more ED-related expense.
That doesn't surprise Charles Pattavina, MD, the chief of emergency medicine at St. Joseph Hospital in Bangor, ME. “You need to be able to take a step back, and look at the big picture sometimes,” he said.
Seeking more precise information “can lead to what I call going down ‘the testing road,’” he said. D-dimer testing, for example, can help screen for pulmonary embolism, which can be missed due to subtle, nonspecific clinical signs. The test unquestionably allows for better decision-making in choosing candidates for CT angiogram.
The same D-dimer test that allows better patient selection for more procedures also frequently gives a false-positive result, said Dr. Pattavina, who also is a former member of board of directors of the American College of Emergency Physicians. He cited the example of a patient with a suspected blood clot in the leg whose D-dimer test was positive, but the scan on one leg—the limb reportedly in pain—proved negative. The physical exam that leads to such scans is legendary in its unreliability, he pointed out.
So what should have prevented the patient from being referred for chest imaging? Patient history and clinician know-how. In this patient, there was no reason to suspect pulmonary embolism in the first place: no family history of clotting disorder, no recent lengthy airplane ride, and no use of birth control pills. “In my opinion, that [first scan] should be the end of the workup unless a scan is going to be done on the other leg,” Dr. Pattavina said.
The risk is that doctors can rely too heavily on testing, giving in to the feeling that “one has to pursue every positive test,” he said. Such technology is no substitute for clinical knowledge and experience, he stressed.
Point-of-care testing is best used to increase clinical knowledge and to quickly complement it, according to reviews of the technology. (New Engl J Med 2011;364:749; Trends Analyt Chem 2011;30:887.) Point-of-care testing can be applied to help tease out which patients need more intensive management when symptoms overlap. One physical complaint in particular crops up in the medical literature as being particularly problematic: vertigo. It can mean anything from an ear infection to a cerebrovascular event.
At the annual meeting of the American Neurological Association in September, results from an analysis of data on dizzy patients who visited U.S. EDs, based on the National Hospital Ambulatory Medical Care Survey, showed what can happen when clinical signs are used to assess dizziness: A diagnosis of stroke may result.
“While this reflects an appropriate assessment of disease probability, it could increase the risk of stroke misdiagnosis in isolated dizziness or dizziness with medical symptoms,” the investigators concluded. Just a few months before, a group in Connecticut suspected the same thing. At Hartford Hospital, they wanted to find if precious brain-preserving minutes could be shaved by using point-of-care testing so they put it to the test for coagulation studies by comparing the international normalized ratio (INR) from samples collected by point-of-care testing and those by standard lab techniques. There was good correlation, and point-of-care testing dramatically slashed time to thrombolytic therapy, they found. (Am J Emerg Med 2011;29:82.) A few years earlier, a French study on the treatment of patients with suspected acute coronary syndromes had a similar time-conserving outcome — point-of-care testing for troponin sharply reduced the period to anti-ischemic treatment. (Acad Emerg Med 2008;15:216.)
Not surprisingly, other investigations have taken up the same challenge in a flurry of studies aimed at determining whether point-of-care testing is a time-saving step equal in precision to the results from the central lab, as well as to other point-of-care technology, and to establish whether tests for the same markers can be used interchangeably. (Crit Care 2011;15:132.) Or as Dr. Campbell at Yale succinctly noted: “Lab testing is best done by lab people unless it's become very simple, on the order of bedside glucose.”
The advances have made readings for cardiac markers and HIV almost immediate, offering up the scenario of home-based testing. (Ann Emerg Med 2011;58[1 Suppl 1]:S74.) But the rapidity of development has not been matched in the realm of infectious disease. Currently, there are nationally designated point-of-care testing centers at work on this problem. At UC Davis, the Point-of-Care Technologies Center is working with Lawrence Livermore National Laboratory in Livermore, CA, to improve point-of-care devices for emergency departments and disaster response sites. How quickly will the diagnosis and treatment of life-threatening bloodstream infections be available?
Methods that use a technique called loop-mediated isothermal amplification, better known as LAMP, offer a way to speed up identification of bacteria and viruses, and other DNA-based methods may lead to faster point-of-care testing for infectious agents as well. But with a truly emergent pathogen, “it would take some time to develop, validate, manufacture, and distribute a test,” said Dr. Campbell, pointing out that the CDC had primers for the 2009 pandemic flu within a couple of weeks though not in quantity. “And for a truly novel pathogen, it would take longer,” he added.
In “Contagion,” the virus that fells people transcontinentally turns out to be the product of fruit that was nibbled by a bat and then ingested by a pig, a bad biologic coincidence. Kristi Koenig, MD, the director of public health preparedness at UC-Irvine, observed that the human decimation didn't come from a weapon armed with infection. Instead, “it was nature.”
• Read the CDC's “Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests; 2010-2011 Influenza Season” at www.cdc.gov/flu/professionals.
• Find out more about the Lawrence Livermore National Laboratory at https://www.llnl.gov.
• Learn about the Center for Disaster Medical Sciences at the University of California, Irvine at http://www.cdms.uci.edu.
• Visit http://www.ucdmc.ucdavis.edu/pathology/poctcenter for more information about the Point-of-Care Technologies Center at the University of California, Davis.
• See what experts at UC-Irvine's Center for Disaster Medical Sciences had to say about the movie “Contagion” at http://bit.ly/UCImovie.
• Comments about his article? Write to EMN at email@example.com.
MRI Now Possible for Patients with Pacemakers or Defibrillators
In the years to come, it may be possible to use magnetic resonance imaging for urgent indications such as stroke or cord compression in patients with pacemakers or defibrillators, a cohort for which there has been general reluctance to perform such studies, the perceived risk being a heating or device malfunction. Experience with this approach at Johns Hopkins seems to show, however, that this is an infrequent occurrence in the right hands. And sometimes the diagnostic imaging simply is a “clinical necessity,” added Saman Nazarian, MD, the director of the ventricular arrhythmia ablation service at Johns Hopkins Hospital in Baltimore.
“We have done urgent MRIs on patients when resources are available,” with only three incidents of interference with the devices, none of which was life-threatening, he noted. Several other centers are adopting the protocol.
Routine ED use, however, would require the availability of clinical resources and possibly further technological advancements to make this more feasible, he pointed out. After 500 such scans demonstrated mostly negligible risk and considerable benefit, it has become an established protocol at the medical center. “It does take careful monitoring,” cautioned Dr. Nazarian, an author of the study. (Ann Intern Med 2011;155:415.) — Anne Scheck