Serum and Urinary Markers of Early Impairment of Gfr in 1 Chronic Kidney Disease Patients: Diagnostic Accuracy of 2 Urinary Beta-trace Protein

26 The screening for chronic kidney diseases (CKD) patients with impaired GFR needs the 27 measurement of serum creatinine (SCr) or cystatin C (SCys). GFR can also be predicted from 28 SCr or SCys with different formulas. Aim of this study, performed in a group of CKD 29 patients with different levels of GFR, was to evaluate the possibility to select the patients with 30 a GFR < 90 mL/min/1.73 m, by means of serum levels and urinary excretion of different 31 low molecular weight proteins (LMWP), cystatin C (Cys), β2-microglobulin (β2M), retinol32 binding protein (RBP), beta-trace protein (BTP), and by means of the derived prediction 33 equations for GFR. 34 In the 295 CKD patients (females 137), at all stages of GFR impairment, a very high 35 correlation was found between GFR (Tc-DTPA), and serum Cr, Cys, β2M, and BTP. All 36 these serum markers showed a similar accuracy as indicators of different GFR impairments. 37 RBP had the lowest correlation with GFR, and was also significantly less accurate. The 38 different prediction formulas derived from gender, anthropometric data and SCr or S-LMWP 39 had a diagnostic accuracy similar to that of serum Cr, Cys, β2M, and BTP. Urinary albumin 40 was inadequate as indicator of any level of GFR impairment. Urinary excretion of Cys and 41 β2M increased significantly only in patients with GFR<30 ml/min/1.73m, while urinary BTP 42 increased already at GFR<90 ml/min/1.73m. In this selected group of CKD patients, the 43 positive predictive value of urinary BTP for GFR<90 ml/min/1.73m was 85%, indicating 44 that, in CKD patients, a urine-based test can predict a slight GFR impairment. 45 46