A Study on Urinary Specific Gravity- in Detection of Proteinuria in Children with Nephrotic Syndrome

Abstract

Introduction: Nephrotic syndrome is a common renal disease that causes pathological proteinuria. Twenty-four hours of urinary protein excretion, which is a commonly accepted method for quantification of proteinuria is timeconsuming and inconvenient. Spot urinary protein creatinine ratio (PCR) has been widely adopted as a practical alternative. Urinary specific gravity or relative
density, which is influenced by proteinuria can be readily measured in the bedside dipstick test and might be used as a rapid screening test for proteinuria. The study aimed to analyze urinary specific gravity, in the detection of proteinuria in children with nephrotic syndrome. Methods: This crosssectional study was conducted in the Department of Pediatric Nephrology (NIKDU), Dhaka, from October 2019 to June 2021, and a total of 153 patients with nephrotic syndrome were enrolled after taking written consent. A urinary heat coagulation test was done. Urine samples were collected for both 24 hours and spot for estimation of urinary protein, urinary creatinine, dipstick protein, and specific gravity by dipstick method. Spot urinary PCR and 24 hours urinary protein were also estimated. Result: Maximum study subjects (44.4%) were 2-5 years old with males (61.4%) predominant. Twenty-four hours UTP was 7.52 ± 7.65 gm/m2/24 hours, 24 hours urinary specific gravity was 1.02 ± 0.02, spot urinary PCR was 21.87 ± 18.24 and specific gravity was 1.02 ± 0.01. Area Under Curve (AUC) of 24 hours urinary specific gravity was 0.551 and spot urinary specific gravity (0.520) was low in prediction of proteinuria (heat coagulation test >++) in children with nephrotic syndrome. But good value of AUC for 24 hours urinary specific gravity (0.789) in prediction of proteinuria (24 hours proteinuria >1000mg/m2/day) and spot urinary specific gravity (0.872) in prediction of proteinuria (spot urinary PCR >2mg/mg) was observed. Area under curve (AUC) of spot urinary specific gravity was (0.719) in prediction of proteinuria (spot dipstick protein >++) and 24 hours urinary specific gravity (0.734) in prediction of proteinuria (24 hours dipstick protein >++) in children with nephrotic syndrome were not poor also. Best sensitivity, specificity, PPV and NPV of 24 hours urinary specific gravity and spot urinary specific gravity were at a cut off value of 1.020. Sensitivity and specificity were poor for both 24 hours urinary specific gravity (64% and 41%) and spot
urinary specific gravity (64% and 39%) in predicting proteinuria defined by heat coagulation test>++ in children with nephrotic syndrome. Sensitivity and specificity of spot urinary specific gravity were 65.5% and 100% as a marker in predicting proteinuria (spot urinary protein creatinine ratio >2 mg/mg) in children with nephrotic syndrome with 100% Positive predictive value and 13.8% negative predictive value. As a marker in predicting proteinuria defined by spot dipstick protein >++, sensitivity and specificity of spot urinary specific gravity were 57.6% and 85.7% with 95% positive predictive value and 30% negative predictive value. In predicting proteinuria (24hrs dipstick protein>++) in children with nephrotic syndrome, sensitivity was 65.7% and specificity was 80% with good positive predictive value 95.8% and 25% negative predictive value. Sensitivity is and specificity is of
24hrs urinary specific gravity were 63.7% and 85.7% respectively as a marker in predicting 24 hours proteinuria (>1000mg/m2/day) in children with nephrotic syndrome with 98.9% positive predictive value and 10.2% negative predictive value. Specificity and sensitivity of urinary specific gravity were significant to detect proteinuria. Conclusion: According to this study’s findings 24 hours of urinary specific gravity can be used as a diagnostic test to detect proteinuria in children with nephrotic syndrome.