BACKGROUND Chronic kidney disease (CKD) encompasses a spectrum of different pathophysiological processes associated with abnormal kidney function and a progressive decline in glomerular filtration rate (GFR). CKD is defined as kidney damage for more than 3 months, as defined by structural or functional abnormalities of kidney, with or without decreased glomerular filtration rate (GFR), which manifests either as pathological abnormalities or markers of kidney damage, including abnormalities in composition of the blood or urine, or abnormalities in imaging tests, with or without kidney damage.