Key Point:

• Determination of sTREM-1 levels shows promise as a rapid way to detect pneumonia in ICU patients. However, it does not determine the causative organism, only the presence of infection.

NANCY, FRANCE—In critically ill patients, problems often arise when microbiologic testing is used to confirm a presumptive diagnosis of pneumonia. The results may not be available for 24 to 48 hours, and in the interim, patients are often treated with unnecessary antibiotics. However, a faster way to detect pneumonia may have been found.

The triggering receptor expressed on myeloid cells (TREM-1) is specifically up-regulated in the presence of microbial products and amplifies the acute inflammatory response to an infection. Researchers in France posited that levels of TREM-1 could be used to identify mechanically ventilated patients with pneumonia. They found that measuring TREM-1 in bronchoalveolar lavage fluid was a highly sensitive, rapid way to diagnose bacterial pneumonia.[1]

One hundred forty-eight ICU patients were enrolled in the study. All were receiving mechanical ventilation and had clinical signs of infectious pneumonia (new pulmonary infiltrates and accompanying symptoms). Mini-bronchoalveolar lavage (BAL) was performed in all patients, and the recovered fluid was divided into two samples. One sample was used for standard microbiologic culture, and the other was tested for soluble TREM-1 (sTREM-1), tumor necrosis factor, and interleukin-1.

According to a post-hoc analysis, 38 patients had community-acquired pneumonia, 46 had ventilator-associated pneumonia, and 64 did not have pneumonia. The patients with pneumonia all had bacterial or fungal infections.

sTERM-1 HAS HIGH SENSITIVITY

According to the researchers, levels of sTREM-1 were higher in the patients with community-acquired or ventilator-associated pneumonia than in the patients without pneumonia, but they did not differ significantly between the two pneumonia groups. An sTREM-1 level of 5 pg/mL or higher was found in 36 of the 38 patients with community-acquired pneumonia and in all of the 46 patients with ventilator-associated pneumonia. In contrast, an sTREM-1 level of 5 pg/mL was found in only six of the 64 patients without pneumonia.

The authors also determined the value of three other variables—a tumor necrosis factor concentration above 150 pg/mL, an interleukin-1 level above 75 pg/mL, and a clinical pulmonary infection score above 6—in predicting the presence of pneumonia. Although all three of these cutoffs helped differentiate patients with pneumonia from those without, none of them were anywhere near as good as an sTREM-1 level above 5 pg/mL. Multiple logistic regression analysis showed that the presence of sTREM-1 in BAL fluid was the strongest independent predictor of pneumonia, yielding an odds ratio of 41.5 (95% confidence interval, 20.9 to 77.6).

TEST FEASIBILITY, APPLICATIONS, ACCURACY

“Determination of sTREM-1 levels is relatively easy,” said Sébastien Gibot, MD, an intensivist at the Hôpital Central in Nancy, France, and lead author of the study. “It takes three to four hours, does not require any specific equipment, and is low in cost.” Dr. Gibot and his colleagues are working on developing a commercial kit that can measure sTREM-1 levels in biological samples at the bedside.

Because none of the study patients had viral pneumonia, the accuracy of sTREM-1 in ruling out a viral infection was not determined, Dr. Gibot admitted. However, he continued, “In vitro experiments seem to support the fact that sTREM-1 is not up-regulated by viruses.”

Dr. Gibot said that he and his colleagues have recently completed a study of critically ill patients with a clinical suspicion of infection. In this study, he explained, “Plasma level of sTREM-1 was shown to accurately predict infection. Moreover, among septic shock patients, there was a correlation between sTREM-1 levels and outcome (ie, the higher the sTREM-1 level, the more favorable the outcome).”

According to the authors, this method for diagnosing pneumonia should be particularly helpful in patients for whom a straightforward diagnosis is not possible. They added that the use of sTREM-1 can be tailored to small groups or even individuals and used to guide treatment decisions for those receiving mechanical ventilation. However, it does not determine the causative organism.

—Gale Jurasek

Reference
1. Gibot S, Cravoisy A, Levy B, et al. Soluble triggering receptor expressed on myeloid cells and the diagnosis of pneumonia. N Engl J Med. 2004;350:451-458.

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