INTRODUCTION
The global prevalence of CKD is estimated to be more than 10%, and CKD has emerged as a public health problem.
Adverse outcomes of CKD such as kidney failure, cardiovascular disease (CVD), and premature death can be prevented or delayed when treatment is initiated in the early stages of disease.
As the earlier stages are often asymptomatic, CKD is usually detected during laboratory evaluation of comorbid conditions.
Glomerular filtration rate (GFR) is considered the index of kidney function, and for convenience is usually estimated using equations instead of by direct measurement.
The Modification of Diet in Renal Disease (MDRD) Study equation [4], which was replaced by the Chronic Kidney Disease Epidemiology Collaboration 2009 equations (CKD-EPI equations) [5], has been used to estimate GFR. However, this tended to underestimate the measured GFR and had less precision, especially at a GFR of 60 mL/min/1.73 m2 or more [6]. The CKD-EPI equations were reported as having less bias, improved precision, and greater accuracy than the MDRD Study equation at a higher GFR of 60 mL/min/1.73 m2 or more [5]. This was also demonstrated for the Korean population [7]. The CKD-EPI equations led to a lower estima-tion of CKD prevalence, primarily due to a lower prev-alence of GFR stage 3, compared to the MDRD Study equation [5]. Persistently increased protein excretion has usually been considered to be a marker of kidney damage, and screening with urine dipsticks has been ac-ceptable for detecting proteinuria [1]. Recently, urinary albumin measurement was recommended as a marker of kidney damage, both for its standardization and also because albumin is the most important protein lost in the urine in most CKD [8]. The albumin-to-creatinine ratio (ACR) is the most preferred value among urinary albumin measurements. Kidney Disease: Improving Global Outcomes (KDIGO) has updated guidelines for defining, diagnosing, staging, and managing CKD since the establishment of the first uniform definitions and staging system for CKD in 2002 [8]. More objective crite-ria, such as the CKD-EPI equations for estimating GFR and classification of albuminuria, have been incorporat-ed. Moreover, GFR stage 3 was subdivided into 3a and 3b. The etiology of CKD was included in the definition; hypertension and diabetes mellitus (DM) are systemic diseases known to cause CKD. Consequently, KDIGO guidelines provide relatively simple and precise meth-ods for early diagnosis of CKD, and tend to yield fewer false positives, thereby avoiding incorrect diagnosis [9].