Comparative diagnostic utility of different urinary biomarkers during pre-albuminuric stages of non-hypertensive type 2 diabetic nephropathy.

Background & Objectives: Activation of renin-angiotensin system and tubulointerstitial damage might be seen in pre-albuminuria stage of diabetic nephropathy (DN). Here, diagnostic utility of four urinary biomarkers [Angiotensinogen (Angio), Interleukin (IL)-18, Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Cystatin] during pre-albuminuria stages of non-hypertensive type 2 diabetes patients was studied.

Methods: A total of 952 type 2 diabetes mellitus (T2DM) patients were screened for nephropathy [estimated glomerular filtration rate (eGFR) ≥120 ml/min and albumin-creatinine ratio (ACR) ≥30], and 120 patients were followed up for one year. At one year, they were classified into hyperfiltration (43), normoalbuminuria (29) and microalbuminuria (48) groups. Another 63 T2DM patients without nephropathy were included as controls. Hypertension, patients on angiotensin-converting enzyme inhibitor/angiotensin receptor blocker, eGFR <60 ml/min/1.73 m and all proteinuric conditions were excluded. All were subjected to testing for urine protein, ACR, HbAC, eGFR, along with urinary biomarkers (IL-18, cystatin-C, NGAL and AGT). Comparative analysis of all the diagnostic tests among different subgroups, correlation and logistic regression was done.

Results: Urinary IL-18/Cr, cystatin/creatinine (Cr) and AGT/Cr levels were higher in groups of hyperfiltration (13.47, 12.11 and 8.43 mg/g), normoalbuminuria (9.24, 11.74 and 9.15 mg/g) and microalbuminuria (11.59, 14.48 and 10.24 mg/g) than controls (7.38, 8.39 and 1.26 mg/g), but NGAL/Cr was comparable. The area under receiver operating characteristic curve (AUC) and sensitivity of AGT to detect early CKD were higher than ACR and eGFR (0.91 and 90.4%, 0.6 and 40% and 0.6 and 37%, respectively). AUC values of other biomarkers, namely IL-18/Cr, cystatin/Cr and NGAL/Cr, were 0.65, 0.64 and 0.51, respectively. Angio/Cr and IL-18/Cr showed correlation with log albuminuria (r=0.3, P=0.00, and r=0.28, P=0.00, respectively). NGAL showed correlation with log eGFR (r=0.28 P=0.00). Multivariate logistic analysis showed that odds ratio of developing nephropathy was 7.5 times with higher values of log Angio/Cr.

Interpretation & Conclusions: Urinary AGT showed a higher diagnostic value than ACR and eGFR followed by IL-18 and cystatin to diagnose DN during pre-albuminuric stages.