Urinary protein/creatinine ratio versus 24-hour proteinuria in the evaluation of lupus nephritis.

INTRODUCTION The urinary protein/creatinine ratio has been used instead of 24-hour proteinuria in Nephrology practice for the follow-up of glomerular diseases, considering the advantages of collection and the low cost. However, there are still doubts as to its applicability both for an isolated evaluation and for the follow-up of patients with lupus nephritis. OBJECTIVE To evaluate 24-hour proteinuria determinations and random urine samples, performing urinary creatinine correction and urinary protein/creatinine ratio in subjects with lupus nephritis. METHODS 24-hour proteinuria and urinary protein/creatinine ratio were determined by conventional methods (automated Pyrogallol for proteinuria and alkaline picrate for creatinine). RESULTS Seventy-eight urine samples of 41 patients diagnosed with systemic lupus erythematosus, according to the American Rheumatology Association, with lupus nephritis, were analyzed, and a good correlation between 24-hour proteinuria and urinary protein/creatinine ratio (r = 0.9010 and r² = 0.813) was observed. However, a poor correlation between random proteinuria (without creatinine correction) versus 24-hour proteinuria (r = 0.635 and r² = 0.403) or versus urinary protein/creatinine ratio (r = 0.754 and r² = 0.569) was seen. CONCLUSION 24-hour proteinuria and urinary protein/creatinine ratio were useful in the follow-up of each case. However, we observed that the absolute values were different, which did not allow the replacement of one for the other during follow-up, especially when this result is used to define the activity of the disease. Based on these results, we suggest a period of intersection from one to the other (two to three determinations by both methods), and the choice of one marker for proteinuria follow-up, if necessary.