The role of procalcitonin as a guide for the diagnosis, prognosis, and decision of antibiotic therapy for lower respiratory tract infections.

Objectives: To assess the value of PCT as a rapid and sensitive marker for diagnosis, prognosis, and therapy of lower respiratory tract bacterial infections necessitating antimicrobial treatment and comparing this marker with other markers of infections including C-reactive protein (CRP) and total white-blood cell counts (WBCs).

Patients And Methods: Sixty Patients were enrolled in the study, they were subjected to complete history taking, physical examination, laboratory investigations including complete blood count, blood gases, blood chemistry, bacteriological culture for sputum and blood, serology for atypicals, and PCR for respiratory viruses, serum C-reactive protein (CRP) and PCT levels were measured. The patients were divided into two groups, group 1 included 26 patients who were culture negative for bacterial infection and group 2 included 34 patients who were culture positive. Group 2 patients were given antibiotic therapy according to the culture sensitivity.

Result: The results revealed that, there was no significant difference between group 1 and group 2 patients as regards age, sex, clinical manifestations, final diagnosis, white blood cell counts, blood gases, number of admitted patients, intensive care unit admission and length of hospital stay. A significant increase of PCT and CRP levels was detected in group 2 compared to group 1 at initial diagnosis. At cutoff value >0.5 ng/ml, PCT gave a sensitivity of 94.1%, specificity of 88.4%, positive predictive value (PPV) of 91.4%, negative predictive value (NPV) of 92% and diagnostic efficiency of 91.6% for diagnosis of respiratory tract bacterial infections. However, at a cutoff value >8 mg/L, CRP gave a sensitivity of 85.2%, specificity of 76.9%, PPV of 82.8%, NPV of 80% and diagnostic efficiency of 81.7%. After antibiotic therapy PCT and CRP levels dropped in group 2 patients as compared to their pre-treatment levels.

Conclusion: Serum PCT level could be used as a novel marker of lower respiratory tract bacterial infections for diagnosis, prognosis and follow up of therapy. This reduces side-effects of an unnecessary antibiotic use, lowers costs, and in the long-term, leads to diminishing drug resistance.