New urinary biomarkers for diabetic kidney disease

Diabetes mellitus (DM) is a chronic disease that affects 366 million people worldwide (6.4% of the adult population) and is expected to rise to 552 million by 2030 [1]. Diabetic kidney disease (DKD) is one of the most serious microvascular complications, which significantly impacts morbidity, mortality and quality of life. DKD occurs in approximately one-third of all people with diabetes and is the leading cause of renal failure in developed and developing countries. The first sign of DKD is considered to be microalbuminuria in clinical practice, while microalbuminuria has several limitations such as lower sensitive and larger variability. Therefore, earlier, more sensitive and specific biomarkers with greater predictability are needed. The aim of this review is to summarize new urinary biomarkers for glomerular injury associated with DKD.Transferrin, a plasma protein, is very similar to albumin in weight. It is more readily filtered through glomerular barrier than albumin for being less anionic. Urinary transferrin is considered to be a more sensitive marker of glomerular damage in diabetic patients based on theory analysis and experimental results. Urinary transferrin excretion shows a good linear relationship with urinary albumin excretion in diabetic patients, and increased urinary transferrin excretion predicts the development of microalbuminuria in type 2 diabetic patients with normoalbuminuria [2]. A systemic review, including 13 studies, indicated that urinary transferrin excretion was a good marker for predicting onset of nephropathy [3]. However, urinary transferrin excretion is not specific for DKD because its elevation can be found in primary glomerulonephritis [4].Immunoglobulin G (IgG) is a protein synthesized and secreted by plasma cells. It has a molecular weight of 150 kDa, which is larger than albumin. Urinary IgG excretion is higher in diabetic patients compared to healthy controls, and its excretion in diabetic patients with normoalbuminuria pred