Assessment of the validity of protein - osmolality ratio in a randomly collected urine specimen, in the estimation of proteinuria in children

Background

Proteinuria is an important marker of kidney disease. Protein-creatinine ratio and protein-osmolality ratio in a spot urine sample have been proposed as alternatives to 24-hour urinary protein excretion, to simplify sample collection and minimize errors due to incorrect sample collection.

Objective

Study was to compare validity of urine protein-osmolality ratio and urine protein-creatinine ratio in a random urine sample against 24-hour urinary protein excretion, to detect proteinuria in a paediatric population.

Methods

A cross sectional descriptive study was conducted by recruiting 85 children with kidney disease from medical wards and nephrology clinic at Lady Ridgeway Hospital, as well as, 56 healthy children aged 3-12 years. Twenty four-hour urine samples and spot urine samples were collected from each participant. Urine protein-osmolality ratio and urine protein-creatinine ratio in the spot urine sample were determined and compared with 24-hour urinary protein excretion. Data was analysed using SPSS statistical package. Standard descriptive methods (mean, median, standard deviation etc.) were used to describe the measured parameters. Receiver Operator Characteristic (ROC) curves were created using protein-osmolality ratio and protein-creatinine ratio as test variables, and 24-hour urinary protein excretion as the ‘gold standard’ variable. Optimum cut of values, maximizing sensitivity and specificity, for protein-osmolality ratio and protein-creatinine ratio was determined using ROC curves.

Results

The optimal value discriminating normal from abnormal protein excretion was determined to be a protein-osmolality ratio of 0.38 mg/L: mOsm/kgH₂O (sensitivity 85.7%, specificity 100%) and a protein-creatinine ratio of 28 mg/mmol (sensitivity 100%, specificity 94%). The cutoff value for discriminating mild from nephrotic proteinuria was to be a protein-osmolality ratio of 2.00 mg/L: mOsm/kgH₂O (sensitivity 91.5%, specificity 100%) and a protein-creatinine ratio of 186 mg/mmol (sensitivity 93%, specificity 98.5%).