Value of micro-proteinuria in combination with ultrasonography of the left renal vein in the diagnosis of orthostatic proteinuria

Abstract

Background: This study aimed to evaluate the clinical value of micro-proteinuria in combination with ultrasonography of the left renal vein (LRV) in the diagnosis of orthostatic proteinuria (OP).

Methods: The patients with suspected OP received West test, upright lordotic position test, Robinson test, ultrasonography of the LRV, and detection of morning urine micro-proteinuria and micro-proteinuria after activity. The sensitivity (Se), specificity (Sp), positive and negative predictive values (PPV and NPV), positive and negative likelihood ratios (PLR and NLR) and Youden's index (YI) for micro-proteinuria, ultrasonography of the LRV and both of them in the diagnosis of OP were analyzed.

Results: From January 2013 to January 2018, 75 patients (M/F: 38/37) were recruited. Sixty patients were diagnosed with OP (M/F: 29/31, median age at onset: 10.6±2.80 years); 15 patients had no OP (M/F: 9/6, median age at onset: 10.9±3.25 years); the LRV entrapment, urine Alb/Cr, IgG/Cr, and NAG/Cr after activity were significantly different between OP group and non-OP group (Z=-3.55, -4.10, -4.01, -3.04, P<0.05). The area under the curve (AUC) of urine Alb/Cr, IgG/Cr, NAG/Cr, and the ratio of anteroposterior (AP) for LRV in the hilar and narrow portions (a/b) was 0.84, 0.84, 0.76 and 0.58, respectively, and the best cut-off value was 13.2 mg/mmol, 2.52 mg/mmol, 0.64 U/mmol and 4.06, respectively. The combination of ultrasonography of the LRV and elevated micro-proteinuria after activity could achieve the Se, Sp, PPV, NPV, PLR (weighted by prevalence, W), NLR (W) and YI at 93.3% (95% CI: 0.83-0.98), 66.7% (95% CI: 0.39-0.87), 91.8% (95% CI: 0.81-0.97), 71.4% (95% CI: 0.42-0.90), 11.2 (95% CI: 4.82-26.00), 0.40 (95% CI: 0.17-0.97) and 60%, respectively, in the diagnosis of OP.

Conclusions: The micro-proteinuria in combination of ultrasonography of the LRV is helpful for the preliminary screening of OP in patients with suspected OP.

Keywords: Orthostatic proteinuria (OP); children; left renal vein entrapment (LRV entrapment); micro-proteinuria.

Figure 1

Patients suspected with OP in clinic and enrolled into hospital were excluded by hematuria and other kidney diseases, failure to complete any one of three clinical tests for OP and insufficient clinical data. OP, orthostatic proteinuria.

Figure 2

ROC for micro-proteinuria and LRV (a/b). AUC for elevated micro-proteinuria (Alb/Cr, IgG/Cr, NAG/Cr and α1Mu/Cr) after activity in the diagnosis of OP was 0.84, 0.84, 0.76 and 0.56; AUC for LRV (a/b) was 0.58. Elevated micro-proteinuria after activity and LRV entrapment on ultrasonography had good performance in the diagnosis of OP, especially the Alb/Cr and IgG/Cr. ROC, receiver operating characteristic; LRV, left renal vein; AUC, area under the curve; OP, orthostatic proteinuria.

Figure 3

Sixty-eight patients had LRV entrapment, while 58 of them (58/68) were diagnosed with OP. Sixty-four patients had elevated micro-proteinuria after activity while 58 of them (58/64) were diagnosed with OP. In the presence of both parametrs, 61 patients had both LRV entrapment and elevated micro-proteinuria after activity, and 56/61 were diagnosed with OP. The Se, Sp, PPV, NPV, PLR (W), NLR (W) and YI for combined use of two parameters were 93.3% (95% CI: 0.83–0.98), 66.7% (95% CI: 0.39–0.87), 91.8% (95% CI: 0.81–0.97), 71.4% (95% CI: 0.42–0.90), 11.2 (95% CI: 4.82–26.00), 0.40 (95% CI: 0.17–0.97) and 60%, respectively. LRV, left renal vein; OP, orthostatic proteinuria; Se, sensitivity; Sp, specificity; PPV, positive predictive values; NPV, negative predictive values; PLR (W), positive likelihood ratios (weighted by prevalence); NLR (W), negative likelihood ratios (weighted by prevalence); YI, Youden’s index.