Urinary Protein Biomarkers in Chronic Kidney Disease

Chronic kidney disease (CKD) is increasingly recognized as an important national and worldwide public health problem because of its consequences on quality of life and high prevalence, existing in up to one-tenth of the adults in developed countries and 13% of the general population [1,2]. Currently used diagnostic and staging tools are mostly based on non-invasive analysis of serum creatinine and/ or urinary albumin and estimation of glomerular filtration rate (eGFR). These biomarkers although widely accepted, frequently fail to identify patients at higher risk of progression or death [3,4]. They are also not reliable parameters for early diagnosis, as rising of serum creatinine levels above normal is only evident after substantial loss of renal function and its level may be affected by additional factors, such as the loss of muscle mass [5]. On the other hand, urinary albumin levels are highly variable and lack of specificity, as patients with reduced eGFR can have normal urinary albumin levels [6,7]. Still, albuminuria has been suggested to be a better predictor of accelerated loss in renal function than eGFR [8]. This is also the case in patients with diabetes mellitus, where microalbuminuria is considered as a risk for development diabetic nephropathy (DN) [9]. Nevertheless, it is still challenging to predict which diabetic patients with normoalbuminuria will develop microalbuminuria and even more, to identify those in whom GFR will decline without ever developing overt albuminuria [3]. According to KDIGO guidelines, all individuals with an estimated GFR <60 mL/min/1.73m 2