Human Neutrophil Lipocalin as an Aid in the Diagnosis of Bacterial Infection in the Emergency Department

This observational study evaluates the diagnostic and prognostic value of Human Neutrophil Lipocalin (HNL) in patients presenting to the Emergency Department (ED) with suspected infection.

Early identification of bacterial infection and sepsis remains a major challenge in emergency care due to the heterogeneity of clinical presentations and the lack of highly accurate diagnostic tools. In particular, distinguishing patients at low risk from those at risk of clinical deterioration is crucial for appropriate treatment decisions, triage, and disposition planning. Delayed recognition of bacterial infection and sepsis is associated with adverse outcomes, especially in patients with atypical presentations.

HNL has emerged as a promising biomarker for differentiating bacterial from viral infections. Previous studies have demonstrated a high diagnostic accuracy of HNL, with reported sensitivity and specificity exceeding 90%, potentially outperforming routinely used biomarkers such as white blood cell count (WBC) and C-reactive protein (CRP). A rapid and reliable biomarker for identifying bacterial infection could support earlier diagnosis, optimize patient management, reduce progression to sepsis, and contribute to more appropriate antibiotic use.

The primary objective of this study is to assess the diagnostic performance of HNL for the detection of bacterial infection in ED patients and to compare its accuracy with routinely used biomarkers, including WBC, CRP, and procalcitonin (PCT).

Secondary objectives include: Comparing the diagnostic performance of HNL measured in serum versus activated Li-heparin whole blood. Evaluating factors that may influence the predictive value of HNL, including age, sex, comorbidities, immunosuppression, and antibiotic treatment. Assessing the prognostic value of HNL for 30-day mortality and comparing its performance with serum lactate, an established predictor of adverse outcomes.

The results of this study may contribute to improved risk stratification and clinical decision-making in patients presenting to the ED with suspected infection.

Inclusion criteria

• Adults presenting to the Emergency Department with suspected infection
• Written informed consent provided prior to enrolment
• Evidence of significant physiological disturbance, defined by abnormal vital signs requiring further medical assessment
• Symptoms suggestive of a respiratory tract infection (e.g. cough with sputum, worsening cough, or breathing difficulties)
• Symptoms suggestive of a urinary tract infection (e.g. pain during urination, frequent urination, or urgency)
• Pain, redness, warmth, or discharge at the site of a vascular catheter or intravenous line
• Signs of a skin or soft tissue infection, including pain, tenderness, swelling, redness, warmth, or pus formation
• Nausea, vomiting, abdominal pain, or jaundice suggestive of a possible abdominal infection
• Headache, neck stiffness, or other symptoms suggestive of a central nervous system infection
• Abnormal vital signs corresponding to a National Early Warning Score (NEWS) of ≥3 points

Exclusion criteria

• Known pregnancy at the time of study enrolment
• Antibiotic treatment that started more than 24 hours before presentation to the Emergency Department
• Inability or unwillingness to provide written informed consent for study participation