Innovative labs provide more than just the usual

Susceptibility testing gets a makeover

Mycobacteriology laboratories should do more than just avoid the twin evils of processing errors and slow turnaround times. They should actively work to improve communication between themselves and the public health administrators and clinicians they serve.

That idea emerged as the principal theme of a gathering of TB controllers, clinicians, and laboratorians last month, when the American Thoracic Society (ATS) convened a working group on susceptibility reporting. The two-day session at the Centers for Disease Control and Prevention in Atlanta is expected to result in the eventual production of some new recommendations for mycobacteriology labs.

The suggestions aired at the session included ways labs can help corral all the data they produce, how they can more clearly present the data, and useful additions they can include on the lab report.

For example, state public health labs could save clinicians a pile of aggravation by serving as a repository for all the lab reports generated in a particular state. "This would be a huge assistance to physicians," says Charles Peloquin, PharmD, director of the Pharmacokinetics Laboratory at National Jewish Hospital in Denver and one of those in attendance at the ATS sessions. "You can easily lose a couple of hours calling labs, trying to find out what’s going on with a particular patient."

Privacy is protected

In New York State, where such a practice is already under way, confidentiality isn’t a problem; clinicians simply enter an identification umber for entry into the data base, notes Max Salfinger, MD, director of the Clinical Mycobacteriology Laboratory for the New York State Health Department and also one of the participants at the ATS session.

Another idea that proved popular was having state labs keep isolates for six to 12 months. That way, they would be available for epidemiologists for molecular studies or for clinicians whose patients were still undergoing treatment.

Public health labs also could perform the function of confirming all first-time positive tests, Salfinger says. "We do it for HIV positive patients; why not for TB patients, too?" he argues. "The impact of a positive on the patient is so dramatic, one should not rely on the first result." He expedites the procedure by putting all such requests onto a fast-track schedule, he adds.

Some of the suggestions the working group put forth looked at what additional information labs could include, such as information about treatment protocols or the names and telephone numbers of expert consultants. Salfinger’s lab throws in these and other extras as well. All positive test results get a sort of care package consisting of the complete CDC recommendations for TB treatment. Salfinger has reasoned that "you never know — the clinician may be an intern or a resident, and perhaps they’ve never treated a case of TB before." He also encloses guidelines from New York City and the CDC on how to manage a TB patient who’s already taking protease inhibitors — just in case. Also listed are the names and phone numbers of all three TB model centers. What keeps him from supplying names and phone numbers of so-called expert consultants, he says, is the suspicion that "here in New York, so many people would be asking, ‘Why am I not listed? I am an expert, too.’"

Ditch the drug or raise the dose?

One point the ATS group hashed over was what exactly goes into a susceptibility test — and how much credence clinicians can accord to the results. Clinicians should bear in mind the distinction between a critical concentration and a minimal inhibitory concentration (MIC). The first, a single drug concentration used to see whether a given isolate is susceptible to a drug, is a quickie version of the second, which consists of a graduated series of drug concentrations to determine the precise strength of an agent needed to stop a bug.

"Critical concentrations came on board in the ‘60s, with the shift from sanatoria research laboratories to the mainstream labs," says Salfinger. Conventional labs "no longer had the resources or knowledge to do expensive or extensive testing" involved in the use of MICs, and they adopted the abbreviated procedure instead.

Can clinicians trust the results? The answer is "yes," says Peloquin, but a much more emphatic "yes" when the critical concentrations possess clinical correlations that have been validated by lengthier time and experience. "The best data we have come from the ‘40s and ‘50s," Peloquin says. "Then people were treated with a single antibiotic. If it said ‘resistant,’ then it was resistant." That isn’t quite the case for some of the newer agents, he says, where the setting of critical thresholds contain an element of faith as well as experience. "For the other drugs, we have a sort of spectrum of confidence," he adds.

Salfinger sees matters a bit differently, particularly when it comes to a lab report that cites INH resistance. "Some of the old data demonstrate that if you have resistance to the low concentration and susceptibility to the high one, one should not abandon this drug," he says. "One should rather increase the dose."

Even if the isolate manages to grow through the higher concentration, some experts argue for hanging onto INH, Salfinger argues. "INH has at least three modes of action," he says. "And with pulmonary TB, there are different populations of organisms. The antimicrobial agent could be acting on one of those subpopulations."

So strong are his convictions on this point that Salfinger said that a physician contemplating abandoning any first-line drug for any reason would do well to consult an expert first. "What the physician assumes is an adverse reaction may not be because of the drug," he says. "Too many physicians give up too easily on powerful antimycobacterial drugs and switch to more toxic second-line drugs." First-line drugs are simply too good to lose, and their second-line cousins are too toxic to take up lightly, he says.