Urinary Podocalyxin Positive-element Occurs In The Early Stage Of Diabetic Nephropathy And Is Correlated With A Clinical Diagnosis Of Diabetic Nephropathy

AimsIn the present study, we choose the podocalyxin, the major antigen of the podocyte, as a marker to test the podocalyxin-positive element (PCX+EL) in urines of diabetic nephropathy patients by flow cytometry using phycoerythrin (PE)-conjugated mouse monoclonal anti-human podocalyxin, providing us the information of podocytes injury. The aim of the study is to test whether urinary podocalyxin-positive element (PCX+EL) can be a marker of early stage of diabetic nephropathy.MethodsFrom January2012to October2012in Shandong Provincial Hospital Affiliated to Shandong University, a total of68type2diabetic nephropathy patients were enrolled in the present study. Diabetic nephropathy patients were divided into three groups according to the degree of urine albumin-to-creatinine ratio (UACR): normoalbuminuria group (UACR<30mg/g, n=21); microalbuminuria group (UACR30-299mg/g, n=25); macroalbuminuria group (UACR ≥300mg/g, n=22). From January2012to October2012,28healthy volunteers were randomly selected as health controls from the Health Examination Center in Shandong Provincial Hospital Affiliated to Shandong University.1. The numbers of urinary podocalyxin-positive elements (PCX+EL) were detected by fluorescence activated cell sorter (FASC) using phycoerythrin (PE)-conjugated mouse monoclonal anti-human podocalyxin.2. The amount of serum cystatin C was measured by immunoturbidimetry in all subjects. We also collected the clinical data of serum creatinine of all subjects from the clinical laboratory of Shandong Provincial Hospital Affiliated to Shandong University.3. We compared the levels of urinary PCX+EL, serum cystatin C and serum creatinine in type2diabetic nephropathy patients with healthy controls; We also compared the amount of urinary PCX+EL, serum cystatin C and serum creatinine in health controls with varying stages of type2diabetic nephropathy patients.4. The correlations between urinary PCX+EL and urinary albumin, serum cystatin C and serum creatinine were examined by the Spearman rank-order correlation.5. The comparison of diagnosis efficiency among urinary PCX+EL, serum cystatin C and serum creatinine was made by receiver operating characteristic (ROC) analysis.Results1. Urinary PCX+EL (p<0.001), serum cystatin C (p<0.001) and serum creatinine (p=0.001) significantly increased in diabetic nephropathy patients compared with health controls.2. Urinary PCX+EL increased significantly in all three patients groups compared with controls (p<0.001for all groups). However, the levels of serum cystatin C increased in diabetic nephropathy patients with microalbuminuria (p<0.001) and macroalbuminuria group (p<0.001) but did not in normoalbuminuria group (p=0.142) compared with health controls. The concentration of serum creatinine only increased in macroalbuminuria group (p<0.001) but did not increased in normoalbuminuria (p=0.117) and microalbuminuria group (p=0.443) compared with health controls.3. Urinary albumin, serum cystatin C and serum creatinine correlated with urinary PCX+EL by the Spearman rank-order correlation (r=0.766, p<0.001for urinary albumin; r=0.785, p<0.001for serum cystatin C; r=0.436, p<0.001for serum creatinine).4. ROC curve analysis indicated that area under the curve (AUC) of urinary PCX+EL (0.966) is higher than that of serum cystatin C (0.857) and serum creatinine (0.726) for discriminating nephropathy between diabetic nephropathy patients and health controls. There was statistically significant difference between the AUC of urinary PCX+EL and that of serum cystatin C and serum creatinine (both p<0.05, Z-test). According to the Youden indices, the cutoff value of3.86arb.units/umol for urinary PCX+EL resulted in the maximum indice, and gave a sensitivity of92.6%and a specificity of96.4%.Conclusion:Urinary podocalyxin positive-element occurs in the early stage of diabetic nephropathy and is correlated with a clinical diagnosis of diabetic nephropathy. It may be a noninvasive marker for the diagnosis of early stage of diabetic nephropathy.