Conventional dipsticks in the screening of microalbuminuria and urinary tract infections. Killing 2 birds with one stone?

The amount of proteins excreted in the urine by normal adults (<150 mg/24 hours) is the result of collection of proteins from serum or renal origin and their degradation products. Under normal physiological conditions the most prevalent of the urine proteins excreted (up to 70 mg per day) is produced in the kidney, urine proteins from serum origin only accounting for up to 22 mg per day. Glomerular filtration barriers indeed markedly limit the filtration of normal to high-molecular weight serum proteins, and the proximal tubule efficiently reabsorbs lowmolecular weight serum proteins (<40 kDa) filtered by the glomeruli. Therefore, an albumin excretion above 20 mg/L (microalbuminuria), increases the albumin to total protein ratio,1 and is considered a diagnostic marker for chronic kidney disease (CKD) even in the presence of normal glomerular filtration rate.2 Microalbuminuria is now also part of the strategy for cardiovascular risk assessment and immunometric systems specific for albuminuria are gradually replacing multiparametric conventional dipstick (MCD) in epidemiological studies.3 However, the increased albumin excretion may also let the total urine protein concentration reach the first turning point of the MCD.4 The semi-quantitative assessment with MCD indeed marks trace results in response to a protein concentration of as little as 150 mg/L and a distinct color change of the 1+ level at around 300 mg/L. The possibility to rule out urinary tract infections (UTI) with MCD was also reported.5 The present study was thus performed to investigate the sensibility and specificity of MCD to estimate microalbuminuria and UTI in epidemiological studies.