The comparison of 24-HOUR urine and spot urine tests in the evaluation of glomerular proteinuria

The reference method for proteinuria is the measurement of the level of protein in the urine for 24 hours. However, collecting urine for 24 hours is difficult and error-prone. In our study, we aimed to compare protein levels in the 24 hours urine and ratio of protein/creatinine in the spotting urine in patients with chronic glomerulonephritis. Two hundred ten patients diagnosed with Type 2-DM, amyloidosis, crescentic nephropathy, membranous nephropathy, IgA nephropathy, C3 nephropathy, focal segmental glomerulosclerosis and systemic lupus erythematosus between 2016-2020 in Dokuz Eylul University Hospital were included in the study. Protein levels in 24-hour urine and protein/creatinine ratio were determined before the biopsy. Patients were classified according to the stage of chronic kidney patients, subgroups of glomerulonephritis, and amount of proteinuria. The correlations between 24-hour urine protein and protein/creatinine ratio were determined in each stage. Patients were divided into 3 groups as mild proteinuria (<1 g/24h), moderate proteinuria (1-4 g/24h), and severe proteinuria (>4g/24h) according to the amount of proteinuria at clinical decision points. The diagnostic performance of predicting urine protein was evaluated by ROC analysis. A cut-off value for protein/creatinine ratio in spot urine was determined by the ROC curve based on the total protein value in 24-hour urine. A significant correlation was found between protein/creatinine ratio and 24-hour urine protein levels in whole group. The significant high correlations were found in whole stages. When patients were classified according to their glomerular pathologies, high correlations in type 2-DM, IgA nephropathy, systemic lupus erythematosus, amyloidosis and focal segmental glomerulosclerosis; moderate in membranous nephropathy, C3 nephropathy and crescentic nephropathy. When classification based on the amount of protein excretion, there was no correlation in those with mild proteinuria, whereas there was an increase in the correlations with the increase in protein excretion. By ROC analysis, When taken the 300 mg/day protein threshold in 24-hour urine for pathological proteinuria, the sensitivity and specificity were determined as 89,2% and 50% in patients with protein/creatinine ratio≥0,655. When a protein amount of 1 g/day for 24 hours urine and 4 g/day for severe pathological proteinuria separation is accepted as the threshold value for a moderate amount of pathological proteinuria. The AUC for the protein/creatinine ratios in spot urine were 0,883 and 0,889, respectively. When 3,53 cut-off is selected for the severity of pathological proteinuria differentiation, patients with a spot urine protein/creatinine ratio above 3,53 have a 24-hour urinary protein value of 88,9% probability, 85,5% sensitivity, and 83,5% specificity. It is concluded that is above 4 g. A multiple regression analysis was performed that examined the relationship between age, spot protein/creatinine ratio and albumin, which may be related to 24h protein level. The model we need to use to estimate the 24-hour urine protein was found y= 14,78 + (0,339 x spot protein/creatinine) – (2,646 X albümin) – (0,065 X age). As a result, we found a high correlation between spot urine protein/creatinine and 24h protein values. In the literature, studies in patients with glomerulonephritis is very few. When all the studies on this subject are evaluated, although the relationship between protein/creatinine ratio and daily protein excretion in spot urine is accepted, there is still no common threshold value. For this reason, we think that the presence of proteinuria detected by spot urine protein/creatinine should be confirmed in 24-hour urine samples until the measurement values are standardized. In further studies to estimate 24-hour urine protein excretion; We think that it may be necessary to use and validate non-linear regression analysis models, including protein/creatinine ratio, age, gender, and stage of chronic kidney disease in spot urine. Keywords: Protein/creatinine ratio in spot urine, protein in 24-hour urine, glomerular proteinuria