BACKGROUND: Previous experimental studies have suggested that the triggering receptor expressed on myeloid cells-1 (TREM-1) is specifically upregulated in the presence of microbial products. OBJECTIVE: To evaluate the diagnostic value of plasma levels of the soluble form of TREM-1 in patients admitted with clinical suspicion of infection. DESIGN: Prospective, noninterventional study conducted between July and September 2003. SETTING: Medical adult intensive care unit at a university hospital in France. PARTICIPANTS: 76 consecutive newly admitted patients who presented with clinically suspected infection and fulfilled at least 2 criteria of the systemic inflammatory response syndrome. MEASUREMENTS: Sensitivity and specificity of plasma soluble TREM-1 levels at admission for the diagnosis of infection. Two independent intensivists blinded to the results of soluble TREM-1 assays retrospectively classified patients as having the systemic inflammatory response syndrome, sepsis, severe sepsis, or septic shock. RESULTS: The systemic inflammatory response syndrome was diagnosed in 29 patients (38%), and sepsis, severe sepsis, or septic shock was diagnosed in the remaining 47 (62%). A plasma soluble TREM-1 level higher than 60 ng/mL was more accurate than any other clinical or laboratory finding for indicating infection (sensitivity, 96% [95% CI, 92% to 100%]; specificity, 89% [CI, 82% to 95%]; positive likelihood ratio, 8.6 [CI, 3.8 to 21.5]; negative likelihood ratio, 0.04 [CI, 0.01 to 0.2]). LIMITATIONS: The study did not enroll patients with mild infections not requiring intensive care unit hospitalization, patients older than 80 years of age, or patients who were immunocompromised. CONCLUSION: In newly admitted critically ill patients, measurement of plasma levels of soluble TREM-1 could help to rapidly identify those with infection.