[Combining the use of dipstick protein and specific gravity accurately predicts pathological proteinuria in Japan]

Dipstick urine analysis is the most common and convenient examination in routine health care. The criteria for abnormal proteinuria is a level of more than (+). However, the interference of urine concentration should be considered in the judgement.

The purpose is to demonstrate the effect of the combined use of specific gravity (SG) in the dipstick judgement to evaluate pathological proteinuria in Japanese people.

The hospital laboratory database of Kitano hospital was searched for urine samples, for patients consulted at our nephrology department from Oct. 2004 to Sep. 2005 (n=1767), and simultaneously assayed for dipstick proteinuria(DSP), SG, urinary protein, urine creatinine (UC) and urinary protein-creatinine ratio (UPC ratio). To generate a model table, samples were stratified according to DSP and SG values. A DSP versus SG matrix (5 x 6)was created, and then all 30 cells were color-coded by the pathological proteinuria proportion (white: < 5%, gray: 5-95%, black: <95%).

SG was positively associated with UC. In the patients, SG < or = 1.005 and DSP(-), 12/70 (17.1%) was > or =300 mg/gCr. Moreover in the patients, both 1.005 < SG < or = 1.010 and DSP(+/-), 21/32 (65.6%) had pathological proteinuria. We confirmed the consistency for this combination table in the urine samples of another 1111 out-patients. Moreover, the area under the curve in DSP(+/-) suggests that the patients whose SG was < or = 1.011 might have pathological proteinuria (sensitivity; 82.1%, specificity; 89.3%).

We recognized that the combination of DSP and SG enhances a more accurate proteinuria judgement. DSP(- approximately +/-) in diluted urine (SG < or = 1.1011) has the potential for pathological proteinuria. Therefore, diluted urine samples should be re-examined.