Kate Johnson

September 06, 2014

WASHINGTON — The use of a procalcitonin (PCT) test to guide antibiotic therapy in patients with lower respiratory tract infections and sepsis is of no value without education on how to interpret the results, a new study suggests.

"Providers were ordering the PCT test, but did not know how to interpret the test result," said lead investigator Meenakshi Ramanathan, PharmD, from the Veterans Affairs North Texas Health Care System in Dallas, Texas.

According to Dr. Ramanathan, the study, presented here at the 54th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), is the first to evaluate PCT's performance in a real-world setting without formal provider education.

"We were not able to see much of a difference in antibiotic de-escalation or discontinuation after a negative test result," she said. "That's where the importance of provider education and algorithm development for established indications comes in."

PCT, an endocrine hormone, rises in response to bacterial but not viral infection, providing potential guidance to clinicians on how to treat infections, Dr. Ramanathan told Medscape Medical News.

"If you're looking at a bacterial vs viral infection, where PCT testing has proven most useful is for lower respiratory infections," she said. "Also, we'll often find a patient with systemic inflammatory response syndrome, but we're not really sure if there's an infectious element, and an elevated PCT test can indicate that maybe they do also have sepsis."

The study retrospectively analyzed 171 consecutive patients who underwent a total of 402 PCT tests. The majority of tests (69.9%) were ordered in the intensive care unit (ICU); 24.4% were ordered on medical or surgical floors.

Most tests (87.51%) were ordered for established indications, such as lower respiratory tract infection (60.35%), sepsis (15.9%), exacerbation of chronic obstructive pulmonary disease (10.6%), or bronchitis (2.1%).

Negative results (PCT < 0.25 µg/L) were seen in 131 patients (32.6%), which would discourage antibiotic use in these patients according to current PCT guidelines, explained Dr. Ramanathan.

Inappropriate Antibiotic Use

Antibiotics were discontinued for 46.8% of patients, whereas for about one quarter of patients, antibiotics were discontinued (16.9%) or de-escalated (6.5%) within 48 hours. The remaining 29.9% had not been prescribed antibiotics in the first place.

A wrinkle in the findings was that among the negative PCT group, 50.6% actually had a documented infection in their chart, suggesting a 49.4% negative predictive value of the PCT test, "which is very low," said Dr. Ramanathan. However, the positive predictive value of the test was 88.3%.

"The way I interpret this is that a negative test result is not reliable. If clinicians felt there was an infection despite the negative PCT test, they would take the test result with a grain of salt, use their clinical judgment, and still treat," she explained.

"But I believe a positive test is useful for indicating the need for antibiotic treatment, especially for established indications like sepsis or lower respiratory tract infection," she added.

 
Elevation of PCT has high correlation for the presence of sepsis due to bacterial infection. Dr. Thomas File
 

The study found no difference in outcomes of mortality, readmission, or length of hospital or intensive care stays between patients with negative PCT tests who had their antibiotics continued vs those whose antibiotics were de-escalated or discontinued.

"This study shows that without the proper guidance, you are not going to get good results with PCT testing," Dr. Ramanathan concluded, adding that at her institution, the test simply increased costs by about $45 per test.

"We're hoping that with the results of this study, we will be able to sit down with our critical care physicians and infectious diseases physicians to come up with an algorithm and accompanying education to allow for appropriate utilization of the test," she said.

The study's finding that PCT testing did not influence treatment decisions is "not surprising, since there was no systematic education provided to practitioners before implementation of the test," commented Thomas File, MD, from the Summa Health System, Akron, Ohio, who was not involved in the research.

Dr. File and his colleagues recently published an observational study ( Ann Pharmacother. 2014 May;48:577-83) in which use of the PCT test, after practitioners were educated in how to interpret it, showed a significant decrease in antibiotic use, length of hospital stay, and 30-day readmission rates.

"Elevation of PCT has high correlation for the presence of sepsis due to bacterial infection. It has a high degree of discrimination between viral and bacterial infection and has been shown to be very useful in the decision to use antimicrobials in community respiratory infections," he told Medscape Medical News.

"Since our study, we have found this test to be very useful in reducing duration of antibiotics," he added.

"In current practice, we recommend PCT determination at onset of sepsis manifestations, and 24 to 48 hours later, since there is often a rapid change based on the bacterial response to therapy. Also, in comparison to the study by Ramanathan et al, we prefer to use the lower level of <0.1 for indication of unlikelihood of bacterial infection," Dr. File explained.

Although PCT testing is used extensively in Europe to guide decisions about treatment with and duration of antimicrobials, there has been less experience in the United States. "There is increased interest, and there are studies ongoing," noted Dr. File.

Dr. Ramanathan and Dr. File have disclosed no relevant financial relationships.

54th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC): Abstract D-179. Presented September 6, 2014.

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