[Urinary measurement of N-terminal B type natriuretic peptide in patients with cardiac failure - highway or byway?].

Urine testing has the advantage of being convenient, familiar to a range of healthcare professionals, and non-invasive. Urine testing for albumin has a well-established role in the management of the diabetic patient and the assessment of renal disease. Urinary measurement of N-terminal B type natriuretic peptide (NTproBNP) has been proposed as a potential tool for detection of cardiac failure. Such an approach would be ideally suited for communitybased diagnosis and potentially useful for the emergency department. Point of care testing (POCT) is already available for measurement of both B type natriuretic peptide (BNP) and NTproBNP in whole blood. If a POCT method for NTproBNP measurement in urine could be developed it could provide a convenient, simple test for heart failure. The clinical diagnosis of heart failure is notoriously difficult. In a systematic review comparing clinical symptoms and signs, the electrocardiogram, and chest radiography, the poor diagnostic efficiency of clinical symptoms and signs was demonstrated and the diagnostic superiority of natriuretic peptide measurements confirmed. It has been estimated that 30%-60% of referrals from primary to secondary care for investigation of suspected heart failure are subsequently found to be inappropriate. A strategy to reduce inappropriate referrals with suspected heart failure would therefore be invaluable, especially in the prevailing climate of scarce healthcare resources. If inappropriate referrals could be reduced by urine POCT for NTproBNP there would be a strong argument on the basis of cost economics to utilize such a test. The cost efficiency of ruling out heart failure using serum B type natriuretic peptide measurement has already been demonstrated. In order to be routinely used, diagnostic testsmust be evidencebased. In assessing the value of urinary measurement it is necessary to consider if the test meets the criteria of being APT: analytically (A) suitable; plausible (P) biologically and clinically; and having a treatment (T) impact. There are a number of analytical factors to be taken into consideration if NTproBNP is to be measured in urine. Current commercial assays for NTproBNP are optimized for use in serum or