To assess the discriminative properties of pleural fluid (PF) N-terminal-proB-type-natriuretic-peptide (NTproBNP) levels in identifying heart failure (HF)-associated pleural effusions (PE).

Objective: To assess the discriminative properties of pleural fluid (PF) N-terminal-proB-type-natriuretic-peptide (NTproBNP) levels in identifying heart failure (HF)-associated pleural effusions (PE).

Hypothesis to be tested: The PF NTproBNP levels are superior to existing methods including Light's criteria, serum/pleural fluid (S/PF) protein gradient, and albumin gradient, in identifying transudates and distinguishing between HF- and non-HF-associated PE.

Design and subjects: A prospective case-control study involving patients with PE requiring thoracentesis, caused by hypervolaemia due to HF, diseases other than HF, and patients with pleural effusion without hypervolaemia. Patient characteristics, PF results and effusion aetiology will be analysed. Patient outcomes will be followed up to 3 months to confirm the aetiology of PE. Clinical management of patients will not be affected.

Study instruments: PF of recruited patients will be analysed for albumin, protein, lactate dehydrogenase (LDH) levels and NTproBNP. The diagnosis of HF will be based on clinical features, serum NTproBNP and echocardiogram.

Main outcome measures: The performance of PF NTproBNP level in identifying HF-associated PE.

Data analysis: The PF NTproBNP level will be compared between effusions of different aetiologies. The optimal pleural fluid NTproBNP level with largest area under the receiver operating characteristic curve in identifying HF-associated PE will be determined. Performance of PF NTproBNP level in identifying HF-associated PE, and other biochemical criteria in identifying transudates will be compared. Echocardiographic findings will be correlated with the PF NTproBNP levels.

Expected results: The diagnostic performance of PF NTproBNP will be significantly better in identifying HF-associated effusion than other biochemical criteria.

Inclusion Criteria:

• Patients hospitalized for heart failure and pleural effusion
• Pleural tapping indicated for pleural fluid analysis.
• Aged 18 years old or above

Exclusion Criteria:

• History of intrapleural therapy (including talc and fibrinolytic) in the ipsilateral pleural space.
• History of surgical decortication or pleurodesis in the ipsilateral pleural space.
• Ipsilateral thoracic or cardiac surgery in the past 3 months.
• Failure to obtain informed consent due to the patient's refusal or cognitive impairment.

Patients who are admitted to the Department of Medicine & Therapeutics, Prince of Wales Hospital (PWH) who fulfil the inclusion and exclusion criteria

Given patient data and privacy concerns, clinical data involving individual patients will not be shared. Data summary tables may later be published along with the research manuscript, and may be shared upon receipt of a reasonable request.