To assess whether pleural fluid and urine amino terminal proB-type natriuretic peptide (NT-proBNP) can distinguish cardiac from non-cardiac causes of pleural effusion.


Blood, urine and pleural fluid were prospectively collected from cats presenting with pleural effusion categorised as cardiac or non-cardiac in origin. NT-ProBNP concentrations were measured using a feline-specific enzyme-linked immunosorbent assay. Groups were statistically compared and receiver operating characteristic curves constructed to determine cut-offs to distinguish cardiac from non-cardiac pleural effusion in plasma, pleural fluid and urine.


Forty cats with pleural effusion (22 cardiac and 18 non-cardiac) were studied. NT-proBNP concentrations in plasma and pleural fluid were strongly correlated. Plasma (P<0·001) and pleural fluid (P<0·001) NT-proBNP concentrations and urinary NT-proBNT/creatinine ratios (P=0·035) were significantly higher in the cardiac group. After receiver operating characteristic curve analysis a plasma NT-proBNP cut-off of 214·3 pmol/mL was suggested [sensitivity=86·4% (95% CI: 66·7 to 95·3%), specificity=88·9% (95% CI: 67·2 to 96·9%)] and a pleural fluid NT-proBNP cut-off of 322·3 pmol/mL was suggested [sensitivity=100% (95% CI: 85·1 to 100%), specificity=94·4% (95% CI: 74·2 to 99·0%)]. No cut-off with adequate sensitivity and specificity for urinary NT-proBNP/creatinine ratios was suggested.

Clinical Significance

Measurement of NT-proBNP in pleural fluid distinguishes cardiac from non-cardiac causes of pleural effusion in cats.