Ventilator-associated pneumonia (VAP) is a common and serious infection among mechanically ventilated ICU patients. Early diagnosis remains challenging because clinical and radiological findings may lack specificity. Procalcitonin (PCT) is a well-established biomarker of bacterial infection, while serum zinc has recently emerged as a potential marker of immune dysfunction and infection severity. This prospective observational cohort study will compare the diagnostic accuracy of serum procalcitonin and serum zinc for the diagnosis of ventilator-associated pneumonia in 84 adult ICU patients. Diagnostic performance will be assessed using ROC curve analysis, sensitivity, specificity, positive predictive value, and negative predictive value. Associations between biomarker levels, inflammatory markers, disease severity scores, and clinical outcomes will also be evaluated.

Ventilator-associated pneumonia (VAP) is a major healthcare-associated infection that develops in patients receiving invasive mechanical ventilation for at least 48 hours. It is associated with prolonged intensive care unit (ICU) stay, increased healthcare costs, greater need for organ support, and increased mortality. Despite advances in critical care, accurate and timely diagnosis of VAP remains challenging because clinical and radiological criteria alone may lack sufficient specificity.

Procalcitonin (PCT) is a well-established biomarker that rises in response to bacterial infections and has been used to support diagnosis, assess disease severity, and guide antibiotic therapy. Zinc is an essential trace element involved in immune regulation, inflammatory response, antioxidant defense, and maintenance of epithelial barrier integrity. Zinc deficiency is common among critically ill patients and has been associated with increased susceptibility to infection and poorer clinical outcomes.

This prospective observational cohort study will be conducted in the Intensive Care Unit of Sohag University Hospital. Eighty-four adult mechanically ventilated ICU patients with suspected ventilator-associated pneumonia will be enrolled. Clinical assessment, laboratory investigations, microbiological cultures, chest imaging, and severity scoring systems including SOFA and CURB-65 will be performed according to the study protocol.

Serum procalcitonin and serum zinc levels will be measured at the time of VAP suspicion and repeated after 72 hours. Blood cultures and respiratory samples will be obtained whenever possible before initiation of antibiotic therapy. Patients will be followed throughout their ICU stay to evaluate disease progression and clinical outcomes.

The primary objective of the study is to compare the diagnostic accuracy of serum procalcitonin and serum zinc for confirmed ventilator-associated pneumonia using receiver operating characteristic (ROC) curve analysis and area under the curve (AUC) measurements.

Secondary objectives include comparison of sensitivity, specificity, positive predictive value, and negative predictive value of both biomarkers at predefined cutoff values; evaluation of the diagnostic performance of a combined biomarker model; assessment of correlations between biomarker levels and inflammatory markers such as C-reactive protein and white blood cell count; and evaluation of associations between biomarker levels, disease severity scores, duration of mechanical ventilation, length of ICU stay, and 28-day mortality.

Inclusion Criteria:

• - Age 18 to 70 years.
• Adult patients admitted to the Intensive Care Unit.
• Receiving invasive mechanical ventilation for at least 48 hours.
• Clinical suspicion of ventilator-associated pneumonia (VAP).
• New or progressive pulmonary infiltrate on chest imaging.
• At least two of the following:
• Fever >38°C or hypothermia <36°C.
• Leukocytosis (>12,000/mm³) or leukopenia (<4,000/mm³).
• Purulent tracheal secretions.
• Worsening oxygenation or increased ventilatory requirements.
• Written informed consent obtained from the patient or legally authorized representative.

Exclusion Criteria:

• - Age less than 18 years or greater than 70 years.
• Known chronic liver disease.
• End-stage renal disease requiring dialysis.
• Immunocompromised patients (including HIV infection, chemotherapy, organ transplantation, or long-term immunosuppressive therapy).
• Current zinc supplementation or known disorders of zinc metabolism.
• Hematologic malignancies.
• Autoimmune diseases requiring immunosuppressive treatment.
• Active non-pulmonary bacterial infection requiring systemic antibiotic therapy.
• Chronic inflammatory diseases that may affect serum zinc levels.
• Pregnancy.
• Refusal or inability to provide informed consent.

The study population will consist of adult patients aged 18 to 70 years admitted to the Intensive Care Unit of Sohag University Hospital who are receiving invasive mechanical ventilation for at least 48 hours and develop clinical suspicion of ventilator-associated pneumonia (VAP). Eligible participants will be enrolled consecutively and evaluated using clinical, radiological, microbiological, and laboratory criteria, including serum procalcitonin and serum zinc measurements.

Individual participant data collected during this study will not be made publicly available. Data will be used solely for the purposes of this research project and related scientific publications. Participant confidentiality and privacy will be protected in accordance with institutional ethical guidelines and applicable regulations.