Body mass index modulates postural proteinuria

Abstract

Dear Sir, In contrast to constant proteinuria, postural proteinuria has been generally regarded as a benign condition [1–4]. However, anecdotal observations suggest that postural proteinuria might sometimes reflect incipient kidney disease [5, 6]. To further address this controversy we recently reassessed 15 subjects with fixed and reproducible postural proteinuria two or more years after the initial diagnosis. After breakfast and after starting an appropriate water load, the subjects came to the clinic. They had been advised to bring along a portion of the first morning urine (‘‘recumbent’’) for determination of the total protein-to-creatinine ratio (reference value: B30 mg/mmol) [7]. The second morning urine sample was collected for urinary sediment analysis and blood was taken for determination of creatinine. Urinary total protein-to-creatinine ratio was also determined with the subjects in a nonrecumbent position for C3 h. Finally height, body weight, and sitting blood pressure (reference: systolic and diastolic blood pressure \90th centile for gender, age, and height in subjects less than 18 years of age and \140/90 mmHg in the remaining subjects) were recorded and a complete physical examination performed. Body mass index was calculated as the body weight in kilograms divided by squared height in meters [8, 9] and the glomerular filtration rate (reference value: C90 ml/[min. 1.73 m]) estimated from height and circulating creatinine using the ‘‘height to creatinine equations’’ [10]. Since body mass index (in kg/m) varies with age, this parameter was also plotted on the body mass index for age and gender charts and expressed as centile adjusted for age and gender [8]. Descriptive statistics are presented as numbers for qualitative data, and as median and interquartile range (which extends from the value at the 25th to that at the 75th centile and includes half of the data points) for quantitative data. v-test (qualitative data) and Mann-Whitney-Wilcoxon test for independent samples (quantitative data) were used for analysis. Statistical significance was set at the 0.05 level. In the recently reevaluated subjects, whose age ranged from 10 to 24 years, the diagnosis of postural proteinuria had been made 2.3–15 years earlier. Physical examination, blood pressure, glomerular filtration rate, urinalysis, and recumbent urinary total proteinto-creatinine ratio were normal in the subjects. Nonrecumbent urinary total protein-to-creatinine ratio G. Milani E. F. Fossali (&) Clinica Pediatrica De Marchi, Foundation IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Via Commenda 9, 20122 Milan, Italy e-mail: mimmofox2000@yahoo.it