[Diagnostic value of soluble urokinase-type plasminogen activator receptor serum levels in adults with idiopathic nephrotic syndrome]. / Valor diagnóstico de los niveles séricos del receptor soluble de la uroquinasa en adultos con síndrome nefrótico idiopático.

INTRODUCTION: Recent studies suggest that soluble urokinase-type plasminogen activator receptor (suPAR) levels could be useful for distinguishing idiopathic focal segmental glomerulosclerosis (FSGS) from other glomerulopathies that cause nephrotic syndrome, but these data have not been confirmed in independent studies. The objective of our study is to analyse whether circulating levels of suPAR are useful for identifying primary kidney disease in patients with nephrotic syndrome secondary to FSGS, minimal change disease or idiopathic membranous nephropathy (MN). METHODS: We measured circulating suPAR at diagnosis in 60 patients with nephrotic syndrome secondary to FSGS, minimal change disease (MCD) and membranous nephropathy (MN). The correlations between suPAR levels and demographic, clinical and biochemical variables were analysed. The sensitivity and specificity of suPAR in distinguishing FSGS patients were analysed by ROC curves. RESULTS: After adjusting for age and renal function, suPAR levels were significantly higher in patients with FSGS than in those with MCD (p<.001), but there were no differences between FSGS and MN (P=.12). A suPAR value ≥3452 pg/ml had a sensitivity of 73.7% and a specificity of 72.5%, with an area under the curve (AUC) of 0.782 ± 0.124, p=.001, for identifying patients with FSGS. After excluding patients with MN, a value ≥3531 pg/ml had a specificity of 99.93% for distinguishing between MCD and FSGS. CONCLUSIONS: suPAR values alone do not distinguish between the three types of glomerulopathy. Nevertheless, after excluding the diagnosis of MN, a suPAR level >3531 pg/ml could have a high specificity (but a low sensitivity) in the diagnosis of FSGS.

[Value of soluble urokinase receptor serum levels in the differential diagnosis between idiopathic and secondary focal segmental glomerulosclerosis]. / Valor de los niveles séricos del receptor soluble de la uroquinasa en el diagnóstico diferencial entre glomeruloesclerosis focal y segmentaria idiopática y secundaria.

BACKGROUND: It has been reported that the circulating level of the soluble urokinase receptor (suPAR) could be useful for distinguishing idiopathic from secondary focal segmental glomerulosclerosis, but the results published are conflicting. In this study, we analyse the intraindividual variability and clinical and anatomopathological variables associated with the suPAR levels and if circulating suPAR levels allow the different forms of focal segmental glomerulosclerosis (FSGS) to be distinguished, i.e., idiopathic forms from secondary FSGS, regardless of the presence of nephrotic syndrome and the activity phase. METHOD: We studied 35 patients affected by idiopathic FSGS and 48 with secondary FSGS (83 in total). We carried out measurements of circulating suPAR at the time of diagnosis and/or after remission and we analysed correlations between suPAR levels and demographic, clinical and biochemical variables. The ability of suPAR to distinguish between both forms of FSGS was analysed by ROC curves and logistic regression analysis. RESULTS: In both forms of FSGS, suPAR levels were independent of proteinuria and the histopathological subtype of FSGS and they were significantly associated with age and renal function. After adjusting for both variables, suPAR levels were significantly higher in patients with idiopathic FSGS, both in the nephrotic syndrome phase and in partial or complete remission. The most sensitive suPAR level (80%) and the most specific (73%) for discriminating between idiopathic and secondary forms was 3443.6 pg/ml (area below curve [ABC] 0.78 ± 0.083, P<.001). In the logistic regression analysis, after adjusting for age, renal function and presence of nephrotic syndrome, suPAR levels were independently associated with the diagnosis of idiopathic FSGS, but the model was poorly adjusted for low risk categories in which it tended to classify primary forms as secondary forms (χ(2) = 11.2 p=.027). CONCLUSIONS: SuPAR levels lack sensitivity for differentiating between idiopathic and secondary FSGS. However, suPAR values greater than 4000 ng/ml are highly specific to primary FSGS, and as such, with a morphological FSGS pattern associated with non-nephrotic proteinuria, they would indicate a low probability of secondary FSGS.