chronic kidney disease ( ckd ) is defined as a structural or functional kidney abnormality lasting for 3 or more months .
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 , which was replaced by the chronic kidney disease epidemiology collaboration 2009 equations ( ckd - epi equations ) , 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 m or more .
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 m or more .
the ckd - epi equations led to a lower estimation of ckd prevalence , primarily due to a lower prevalence of gfr stage 3 , compared to the mdrd study equation .
persistently increased protein excretion has usually been considered to be a marker of kidney damage , and screening with urine dipsticks has been acceptable for detecting proteinuria .
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
. 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 .
more objective criteria , such as the ckd - epi equations for estimating gfr and classification of albuminuria , have been incorporated . moreover ,
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 methods for early diagnosis of ckd , and tend to yield fewer false positives , thereby avoiding incorrect diagnosis .
the number of patients treated with renal replacement therapy ( rrt ) including dialysis and transplantation has increased dramatically in korea , from 28,046 in 2000 to 75,042 in 2013 .
the prevalence of rrt was 1,446 patients per million population ( pmp ) , with an incidence of 234 pmp in 2013 .
the cause of kidney failure was estimated to be dm in 48.0% , hypertension in 19.7% , and chronic glomerulonephritis in 8.3% of cases . the previously reported ckd prevalence calculated from the mdrd study equation
the ckd prevalence calculated from the mdrd study equation alone was 8.8% in 2005 and 7.2% in 2007 in korea national health and nutrition examination survey ( knhanes ) subjects aged  20 ; the prevalence calculated using the mdrd study equation with the dipstick proteinuria method has tended to decrease since 2001 in men and since 2005 in women among knhanes i to iv ( 1998 to 2009 ) subjects aged  20 . since there are no reports on ckd prevalence using the ckd - epi equations to estimate gfr and acr to measure albuminuria for koreans , a new analysis of ckd prevalence is necessary .
this study was therefore designed to investigate the prevalence of ckd in the korean population using knhanes samples , based on the definition and classification by kdigo 2012 guidelines , as well as the impact of changes through a comparison of the ckd - epi and mdrd study equations for the estimation of gfr , and the associations between ckd and major risk factors , including dm , hypertension , age , and gender .
this retrospective , population - based study was performed using data acquired by the knhanes v from 2010 to 2012 .
knhanes v was a cross - sectional , nationally representative survey with a multistage , stratified , and probability sampling design based on sex , age , and geographical area using household registries .
knhanes , composed of a health questionnaire survey , physical examination , and nutrition survey , has been conducted periodically since 1998 to assess the health and nutritional status of the non - institutionalized korean population by the korea centers for disease control and prevention ( kcdc ) .
the study protocol was approved by the institutional review board of kcdc ( 2010 - 02con-21-c ) , and written informed consents were obtained from all subjects or their guardians .
knhanes v data of 2010 were excluded as urine albumin was not measured until 2011 .
the inclusion criteria were ( 1 ) adults aged  19 , and ( 2 ) available serum creatinine ( scr ) , urine albumin , and urine creatinine test results .
individuals aged  19 were classified as adults in the study due to the kdigo guideline s classification of children as birth to 18 . the health examination was performed in a mobile health examination center .
was measured by a trained nurse following a standard protocol in accordance with the recommendations of the american heart association .
three readings were obtained via mercury sphygmomanometer ( baumanometer , baum , copiague , ny , usa ) , and the mean of the second and third reading was reported as the final bp for individual participants .
body mass index ( bmi ) was calculated as body weight divided by the square of the height , and expressed in units of kg / m .
blood samples were collected from the median cubital or cephalic veins by a skilled nurse after an overnight fast .
a random urine sample ( first urine in the morning , if possible ) was obtained in a conical container .
the urine and pretreated blood samples were refrigerated and transported to the central laboratory within the day ( neodin medical institute , seoul , korea ) .
serum creatinine and urine creatinine were assayed by colorimetry using creatinine - hr l - type wako ( wako , osaka , japan ) following the jaffe method ; fasting glucose concentration ( fasting blood glucose , fbg ) by an enzymatic method using pureauto s glu ( sekisui , osaka , japan ) ; total cholesterol , high density lipoprotein cholesterol ( hdl - c ) , and triglycerides by an enzymatic method ; and urine albumin by turbidimetric assay using albumin ( roche , mannheim , germany ) , all performed using a hitachi automatic analyzer 7600 ( hitachi high - technologies co. , tokyo , japan ) , which was calibrated using calibrator for automated systems ( roche diagnostics , indianapolis , in , usa ) .
glycated hemoglobin ( a1c ) was assayed by high performance liquid chromatography ( hlc-723g7 a1c , tosoh , tokyo , japan ) .
urine chemistry was tested by test strip ( urysis 2400 cassette , roche ) using urisys 2400 ( roche ) .
low density lipoprotein cholesterol ( ldl - c ) was computed using the friedewald formula when triglycerides were less than 400 mg / dl .
ckd was defined and classified based on kdigo guidelines using both gfr and urinary acr .
gfr was estimated using ckd - epi equations , taking into account gender and serum creatinine .
individuals with gfr < 60 ml / min/1.73 m or acr  30 mg / g were classified as ckd patients . hypertension was defined as having a systolic blood pressure ( sbp ) of  140 mmhg or a diastolic blood pressure ( dbp ) of  90 mmhg , or having received a physician s diagnosis .
dm was defined as having a1c  6.5% , fbg of  126 mg / dl , or having received a physician s diagnosis .
dyslipidemia was defined as having total cholesterol  240 mg / dl , ldl - c  160 mg / dl , hdl - c < 40 mg / dl , triglycerides  200 mg / dl , or having received a physician s diagnosis .
analyses were performed incorporating the sampling weights to obtain unbiased estimates from the complex knhanes sampling design following the knhanes recommendations .
the study population was separated as a subpopulation , and the analysis was carried out on the entire knhanes samples for 2011 and 2012 to represent all korean adults without bias .
in addition , weight adjustments were applied to the user - missing values to prevent skews in sampling design .
the demographic and biochemical characteristics of the study population were summarized and compared using the complex samples general linear model for continuous variables and the complex samples chi - square test for categorical variables .
the mean and the 95% confidence interval ( ci ) were presented for data on continuous variables , whereas unweighted count with weighted percentage was presented for data on categorical variables .
the complex samples chi - square test was used to analyze prevalence of ckd by gfr with acr categories , and gfr comparison between mdrd and ckd - epi equations was expressed as a weighted percentage .
a subpopulation was added to strata when performing the complex samples chi - square test .
associations of ckd , gfr , and acr categories with various risk factors , including gender , age , bmi , dm , hypertension , and dyslipidemia were expressed as an odds ratio ( or ) , which was calculated using complex samples multivariate logistic regression analyses .
this retrospective , population - based study was performed using data acquired by the knhanes v from 2010 to 2012 .
knhanes v was a cross - sectional , nationally representative survey with a multistage , stratified , and probability sampling design based on sex , age , and geographical area using household registries .
knhanes , composed of a health questionnaire survey , physical examination , and nutrition survey , has been conducted periodically since 1998 to assess the health and nutritional status of the non - institutionalized korean population by the korea centers for disease control and prevention ( kcdc ) .
the study protocol was approved by the institutional review board of kcdc ( 2010 - 02con-21-c ) , and written informed consents were obtained from all subjects or their guardians .
knhanes v data of 2010 were excluded as urine albumin was not measured until 2011 .
the inclusion criteria were ( 1 ) adults aged  19 , and ( 2 ) available serum creatinine ( scr ) , urine albumin , and urine creatinine test results .
individuals aged  19 were classified as adults in the study due to the kdigo guideline s classification of children as birth to 18 .
blood pressure ( bp ) was measured by a trained nurse following a standard protocol in accordance with the recommendations of the american heart association .
three readings were obtained via mercury sphygmomanometer ( baumanometer , baum , copiague , ny , usa ) , and the mean of the second and third reading was reported as the final bp for individual participants .
body mass index ( bmi ) was calculated as body weight divided by the square of the height , and expressed in units of kg / m .
blood samples were collected from the median cubital or cephalic veins by a skilled nurse after an overnight fast . a random urine sample ( first urine in the morning , if possible )
the urine and pretreated blood samples were refrigerated and transported to the central laboratory within the day ( neodin medical institute , seoul , korea ) .
serum creatinine and urine creatinine were assayed by colorimetry using creatinine - hr l - type wako ( wako , osaka , japan ) following the jaffe method ; fasting glucose concentration ( fasting blood glucose , fbg ) by an enzymatic method using pureauto s glu ( sekisui , osaka , japan ) ; total cholesterol , high density lipoprotein cholesterol ( hdl - c ) , and triglycerides by an enzymatic method ; and urine albumin by turbidimetric assay using albumin ( roche , mannheim , germany ) , all performed using a hitachi automatic analyzer 7600 ( hitachi high - technologies co. , tokyo , japan ) , which was calibrated using calibrator for automated systems ( roche diagnostics , indianapolis , in , usa ) .
glycated hemoglobin ( a1c ) was assayed by high performance liquid chromatography ( hlc-723g7 a1c , tosoh , tokyo , japan ) .
urine chemistry was tested by test strip ( urysis 2400 cassette , roche ) using urisys 2400 ( roche ) .
low density lipoprotein cholesterol ( ldl - c ) was computed using the friedewald formula when triglycerides were less than 400 mg / dl .
ckd was defined and classified based on kdigo guidelines using both gfr and urinary acr .
gfr was estimated using ckd - epi equations , taking into account gender and serum creatinine .
individuals with gfr < 60 ml / min/1.73 m or acr  30 mg / g were classified as ckd patients .
hypertension was defined as having a systolic blood pressure ( sbp ) of  140 mmhg or a diastolic blood pressure ( dbp ) of  90 mmhg , or having received a physician s diagnosis .
dm was defined as having a1c  6.5% , fbg of  126 mg / dl , or having received a physician s diagnosis .
dyslipidemia was defined as having total cholesterol  240 mg / dl , ldl - c  160 mg / dl , hdl - c < 40 mg / dl , triglycerides  200 mg / dl , or having received a physician s diagnosis .
analyses were performed incorporating the sampling weights to obtain unbiased estimates from the complex knhanes sampling design following the knhanes recommendations .
the study population was separated as a subpopulation , and the analysis was carried out on the entire knhanes samples for 2011 and 2012 to represent all korean adults without bias .
in addition , weight adjustments were applied to the user - missing values to prevent skews in sampling design .
the demographic and biochemical characteristics of the study population were summarized and compared using the complex samples general linear model for continuous variables and the complex samples chi - square test for categorical variables .
the mean and the 95% confidence interval ( ci ) were presented for data on continuous variables , whereas unweighted count with weighted percentage was presented for data on categorical variables .
the complex samples chi - square test was used to analyze prevalence of ckd by gfr with acr categories , and gfr comparison between mdrd and ckd - epi equations was expressed as a weighted percentage .
a subpopulation was added to strata when performing the complex samples chi - square test .
associations of ckd , gfr , and acr categories with various risk factors , including gender , age , bmi , dm , hypertension , and dyslipidemia were expressed as an odds ratio ( or ) , which was calculated using complex samples multivariate logistic regression analyses .
all statistical analyses were performed using ibm spss version 21.0 ( ibm corp . , armonk , ny , usa ) . the statistical significance level was set at p < 0.05 .
among the total sample size of 16,576 from 2011 and 2012 , 64.7% satisfied the inclusion criteria ( 10,636 individuals : 5,388 and 5,248 from 2011 and 2012 , respectively ) as shown in fig .
the composition of neither the total adults nor the study population was statistically different between 2011 and 2012 ( p = 0.232 and p = 0.087 , respectively ) . the study population comprised 81.8% of total adults ( 81.0% and 82.7% from 2011 and 2012 , respectively ,
the anthropometric and biochemical characteristics of the study population in 2011 and 2012 were comparable , except for hdl - c , ldl - c , and prevalence of dyslipidemia ( table 1 ) .
the percentage of men was 52.6% , and the mean age was 45.8 years ( 95% ci , 45.2 to 46.3 ) .
mean serum creatinine was 0.86 mg / dl ( 95% ci , 0.85 to 0.86 ) , with an estimated gfr of 96 ml / min/1.73 m ( 95% ci , 96 to 97 ) .
mean acr was 18 mg / g ( 95% ci , 15 to 21 ) , with urine albumin 22 g / ml ( 95% ci , 19 to 26 ) and urine creatinine 165 mg / dl ( 95% ci , 163 to 168 ) .
mean sbp was 118 mmhg ( 95% ci , 117 to 119 ) , and dbp 76 mmhg ( 95% ci , 76 to 77 ) .
mean fbg was 97 mg / dl ( 95% ci , 97 to 98 ) , and a1c 5.7% ( 95% ci , 5.67 to 5.71 ) .
mean total cholesterol , hdl - c , ldl - c , and triglycerides were 190 mg / dl ( 95% ci , 188 to 191 ) , 49 mg / dl ( 95% ci , 49 to 50 ) , 114 mg / dl ( 95% ci , 113 to 115 ) , and 136 mg / dl ( 95% ci , 133 to 139 ) , respectively .
the ckd prevalence in korean adults was estimated as 7.9% ( 7.8% in 2011 and 8.0% in 2012 , p = 0.770 ) ( table 1 ) .
the prevalence of hypertension , dm , and dyslipidemia was 27.8% ( 27.2% in 2011 and 28.4% in 2012 , p = 0.380 ) , 9.3% ( 9.7% in 2011 and 9.0% in 2012 , p = 0.306 ) , and 32.8% ( 34.6% in 2011 and 31.0% in 2012 , p = 0.004 ) , respectively .
the distribution of ckd prevalence classified by the gfr and acr categories is shown in table 2 .
the prevalence of low , moderately increased , high , and very high ckd risk prognosis was 92.0% , 6.3% , 1.1% , and 0.6% , respectively .
the prevalence of gfr < 60 ml / min/1.73 m was 2.2% , whereas acr  30 mg / g was 6.5% ( a2 of 5.6% and a3 of 0.9% ) .
the prevalence of acr  30 mg / g in individuals with gfr  60 ml / min/1.73
the prevalence of each estimated gfr category using ckd - epi equations and the mdrd study equation is shown in fig .
the prevalence of g1 was 67.9% and 59.4% by ckd - epi equations and the mdrd study equation , and g2 was 29.8% and 38.7% , respectively .
the prevalence of gfr < 60 ml / min/1.73 m by the mdrd study equation was 2.0% , which was significantly less than the 2.2% by ckd - epi equations ( p < 0.001 ) .
the prevalence of at least 1 + proteinuria in a1 , expected to be fully negative , was 0.1% whereas  or  proteinuria in a2 and a3 , expected to be fully positive , were 5.3% and 0.3% , respectively .
some interactions between demographic covariates , such as gender , age , and bmi , were present .
the risk of bmi  25 for men was higher than for women ( or , 1.296 ; 95% ci , 1.164 to 1.443 ; p < 0.001 ) .
the study population was stratified into six groups by age in 10-year increments : 19 to 28 , 29 to 38 , 39 to 48 , 49 to 58 , 59 to 68 , and  68 .
the ors of increasing age ( using the age group of 19 to 28 as a reference ) to bmi  25 were 1.731 ( 95% ci , 1.400 to 2.139 ) , 2.150 ( 95% ci , 1.757 to 2.632 ) , 1.689 ( 95% ci , 1.376 to 2.074 ) , 2.092 ( 95% ci , 1.690 to 2.590 ) , and 1.554 ( 95% ci , 1.255 to 1.924 ; p = 0.001 ) , respectively .
in addition , the composition of men significantly decreased in the  49 age groups ; ors of men to increasing age ( using the age group of 19 to 28 as a reference ) were 0.931 ( 95% ci , 0.784 to 1.105 ) , 0.894 ( 95% ci , 0.750 to 1.065 ) , 0.735 ( 95% ci , 0.625 to 0.864 ) , 0.691 ( 95% ci , 0.578 to 0.825 ) , and 0.505 ( 95% ci , 0.421 to 0.607 ; p = 0.001 ) , respectively . thus , the association analysis was performed separately for each gender . because ckd is defined by both gfr and albuminuria , the associations between the risk factors and either decreased gfr or increased acr were also studied .
the frequency of women among ckd patients was 54.3% , which was significantly higher than that for men ( p < 0.001 ) . among individuals with acr  30 mg / g
, women accounted for 55.4% ( p < 0.001 ) ; however , women constituted 48.7% of gfr < 60 ml / min/1.73 m ( p = 0.683 ) .
the ors of gender to ckd , acr  30 mg / g , and gfr < 60 ml / min/1.73 m for men were 1.354 ( 95% ci , 1.162 to 1.577 ; p
< 0.001 ) , and 1.057 ( 95% ci , 0.811 to 1.376 ; p = 0.683 ) , respectively .
the prevalence of bmi  25 , ckd , gfr < 60 ml / min/1.73 m , acr  30 mg / g , dm , hypertension , and dyslipidemia stratified by age categories in men and women are shown in tables 4 and 5 .
the ors of covariates to the prevalence of ckd , gfr < 60 ml / min/1.73 m , and acr  30 mg / g , after adjusting for age , bmi , hypertension , dm , and dyslipidemia in men and women are listed in table 6 .
hypertensive patients showed a higher risk of ckd than the normotensive population ( or , 3.394 for men ; or , 2.935 for women ; both p < 0.0001 ) .
the ors of hypertension to cause albuminuria were 3.351 ( p < 0.001 ) for men and
3.067 ( p < 0.001 ) for women , and to decrease gfr , 3.436 ( p < 0.001 ) for men and 1.904 ( p = 0.006 ) for women .
diabetic patients showed a higher risk of ckd than the nondiabetic population ( or , 3.145 for men ; or , 1.983 for women ; both p < 0.001 ) .
the ors of dm to cause albuminuria were 3.144 ( p < 0.001 ) for men and
2.022 ( p < 0.001 ) for women , and to decrease gfr 1.965 ( p = 0.004 ) for men and 1.764 ( p = 0.013 ) for women .
dyslipidemia showed a significant association with ckd in women ( or , 1.324 ; p = 0.023 ) , but not in men ( or , 1.175 ; p = 0.243 ) .
increasing age and obesity ( bmi  25 ) showed a positive correlation with ckd .
among the total sample size of 16,576 from 2011 and 2012 , 64.7% satisfied the inclusion criteria ( 10,636 individuals : 5,388 and 5,248 from 2011 and 2012 , respectively ) as shown in fig .
the composition of neither the total adults nor the study population was statistically different between 2011 and 2012 ( p = 0.232 and p = 0.087 , respectively ) . the study population comprised 81.8% of total adults ( 81.0% and 82.7% from 2011 and 2012 , respectively ,
the anthropometric and biochemical characteristics of the study population in 2011 and 2012 were comparable , except for hdl - c , ldl - c , and prevalence of dyslipidemia ( table 1 ) .
the percentage of men was 52.6% , and the mean age was 45.8 years ( 95% ci , 45.2 to 46.3 ) .
mean serum creatinine was 0.86 mg / dl ( 95% ci , 0.85 to 0.86 ) , with an estimated gfr of 96 ml / min/1.73 m ( 95% ci , 96 to 97 ) .
mean acr was 18 mg / g ( 95% ci , 15 to 21 ) , with urine albumin 22 g / ml ( 95% ci , 19 to 26 ) and urine creatinine 165 mg / dl ( 95% ci , 163 to 168 ) .
mean sbp was 118 mmhg ( 95% ci , 117 to 119 ) , and dbp 76 mmhg ( 95% ci , 76 to 77 ) .
mean fbg was 97 mg / dl ( 95% ci , 97 to 98 ) , and a1c 5.7% ( 95% ci , 5.67 to 5.71 ) .
mean total cholesterol , hdl - c , ldl - c , and triglycerides were 190 mg / dl ( 95% ci , 188 to 191 ) , 49 mg / dl ( 95% ci , 49 to 50 ) , 114 mg / dl ( 95% ci , 113 to 115 ) , and 136 mg / dl ( 95% ci , 133 to 139 ) , respectively .
the ckd prevalence in korean adults was estimated as 7.9% ( 7.8% in 2011 and 8.0% in 2012 , p = 0.770 ) ( table 1 ) .
the prevalence of hypertension , dm , and dyslipidemia was 27.8% ( 27.2% in 2011 and 28.4% in 2012 , p = 0.380 ) , 9.3% ( 9.7% in 2011 and 9.0% in 2012 , p = 0.306 ) , and 32.8% ( 34.6% in 2011 and 31.0% in 2012 , p = 0.004 ) , respectively .
the distribution of ckd prevalence classified by the gfr and acr categories is shown in table 2 .
the prevalence of low , moderately increased , high , and very high ckd risk prognosis was 92.0% , 6.3% , 1.1% , and 0.6% , respectively .
the prevalence of gfr < 60 ml / min/1.73 m was 2.2% , whereas acr  30 mg / g was 6.5% ( a2 of 5.6% and a3 of 0.9% ) .
the prevalence of acr  30 mg / g in individuals with gfr  60 ml / min/1.73
the prevalence of each estimated gfr category using ckd - epi equations and the mdrd study equation is shown in fig .
2 . the prevalence of g1 was 67.9% and 59.4% by ckd - epi equations and the mdrd study equation , and g2 was 29.8% and 38.7% , respectively .
the prevalence of gfr < 60 ml / min/1.73 m by the mdrd study equation was 2.0% , which was significantly less than the 2.2% by ckd - epi equations ( p < 0.001 ) .
the prevalence of at least 1 + proteinuria in a1 , expected to be fully negative , was 0.1% whereas  or  proteinuria in a2 and a3 , expected to be fully positive , were 5.3% and 0.3% , respectively .
some interactions between demographic covariates , such as gender , age , and bmi , were present .
the risk of bmi  25 for men was higher than for women ( or , 1.296 ; 95% ci , 1.164 to 1.443 ; p < 0.001 ) .
the study population was stratified into six groups by age in 10-year increments : 19 to 28 , 29 to 38 , 39 to 48 , 49 to 58 , 59 to 68 , and  68 .
the ors of increasing age ( using the age group of 19 to 28 as a reference ) to bmi  25 were 1.731 ( 95% ci , 1.400 to 2.139 ) , 2.150 ( 95% ci , 1.757 to 2.632 ) , 1.689 ( 95% ci , 1.376 to 2.074 ) , 2.092 ( 95% ci , 1.690 to 2.590 ) , and 1.554 ( 95% ci , 1.255 to 1.924 ; p = 0.001 ) , respectively .
in addition , the composition of men significantly decreased in the  49 age groups ; ors of men to increasing age ( using the age group of 19 to 28 as a reference ) were 0.931 ( 95% ci , 0.784 to 1.105 ) , 0.894 ( 95% ci , 0.750 to 1.065 ) , 0.735 ( 95% ci , 0.625 to 0.864 ) , 0.691 ( 95% ci , 0.578 to 0.825 ) , and 0.505 ( 95% ci , 0.421 to 0.607 ; p = 0.001 ) , respectively . thus , the association analysis was performed separately for each gender . because ckd is defined by both gfr and albuminuria , the associations between the risk factors and either decreased gfr or increased acr were also studied .
the frequency of women among ckd patients was 54.3% , which was significantly higher than that for men ( p < 0.001 ) . among individuals with acr  30 mg / g ,
women accounted for 55.4% ( p < 0.001 ) ; however , women constituted 48.7% of gfr < 60 ml / min/1.73 m ( p = 0.683 ) .
the ors of gender to ckd , acr  30 mg / g , and gfr < 60 ml / min/1.73 m for men were 1.354 ( 95% ci , 1.162 to 1.577 ; p
< 0.001 ) , 1.416 ( 95% ci , 1.193 to 1.682 ; p < 0.001 ) , and 1.057 ( 95% ci , 0.811 to 1.376 ; p = 0.683 ) , respectively .
the prevalence of bmi  25 , ckd , gfr < 60 ml / min/1.73 m , acr  30 mg / g , dm , hypertension , and dyslipidemia stratified by age categories in men and women are shown in tables 4 and 5 .
the ors of covariates to the prevalence of ckd , gfr < 60 ml / min/1.73 m , and acr  30 mg / g , after adjusting for age , bmi , hypertension , dm , and dyslipidemia in men and women are listed in table 6 .
hypertensive patients showed a higher risk of ckd than the normotensive population ( or , 3.394 for men ; or , 2.935 for women ; both p < 0.0001 ) .
the ors of hypertension to cause albuminuria were 3.351 ( p < 0.001 ) for men and
3.067 ( p < 0.001 ) for women , and to decrease gfr , 3.436 ( p < 0.001 ) for men and 1.904 ( p = 0.006 ) for women .
diabetic patients showed a higher risk of ckd than the nondiabetic population ( or , 3.145 for men ; or , 1.983 for women ; both p < 0.001 ) .
the ors of dm to cause albuminuria were 3.144 ( p < 0.001 ) for men and
2.022 ( p < 0.001 ) for women , and to decrease gfr 1.965 ( p = 0.004 ) for men and 1.764 ( p = 0.013 ) for women .
dyslipidemia showed a significant association with ckd in women ( or , 1.324 ; p = 0.023 ) , but not in men ( or , 1.175 ; p = 0.243 ) . increasing age and obesity ( bmi  25 ) showed a positive correlation with ckd .
this study is the first to report ckd prevalence using gfr estimated by using ckd - epi equations together with acr for albuminuria in the korean population .
the prevalence of ckd was 7.9% in the knhanes samples of 2011 and 2012 in korean adults aged  19 , and the ckd risk prognosis was reported in table 2 .
the ckd risk prognosis from moderately increased to very high reported in this study was lower than that in the usa .
gfr and albuminuria are independent and complementary predictors of important clinical outcomes , including ckd progression , end - stage renal disease , acute kidney injury , cardiovascular mortality , and all - cause mortality [ 16 - 19 ] .
the frequencies of gfr < 60 ml / min/1.73 m showed sharp increases starting from around age 50 for men and 60 for women , whereas those of acr  30 mg / g increased relatively gradually , starting from earlier ages , as shown in table 4 and 5 .
the rate of decline of measured gfr was reported to double in kidney transplantation donors aged > 45 years .
the prevalence of estimated gfr < 60 ml / min/1.73 m using ckd - epi equations and the mdrd study equation was 2.2% and 2.0% in this study , but 2.6% and 3.2% , respectively in the previous study .
the statistical method used in the current study was complex sample analysis incorporating sampling weight , in contrast to the previous study which did not consider weight in the analysis .
the frequencies of gfr stage g1 and g2 by ckd - epi equations were 67.7% and 29.8% , whereas those by the mdrd study equation were 59.4% and 38.7% , respectively , in this study .
these numbers are comparable to the previous study , considering the different analytical methods ; the frequencies of gfr stage g1 and g2 by ckd - epi equations were 64.5% and 28.9% , whereas those by the mdrd study equation were 47.6% and 49.2% , respectively .
these results confirm the tendency to underestimate gfr by the mdrd study equation when gfr is 60 ml / min/1.73 m or greater .
the previous report of lower prevalence of gfr stage g3 using ckd - epi equations than with the mdrd study equation was not observed in this study . among the population of the previous study , the frequencies of g3 by ckd - epi equations and the mdrd study equation ( 33.2% and 37.2% , respectively ) were far greater than those among the korean population ( 2.1% and 1.9% , respectively ) .
the prevalence of acr  30 mg / g in the entire study population , and acr  30 mg / g in individuals with gfr  60 ml / min/1.73
the prevalence of acr  30 mg / g in the entire study population and acr  30 mg / g in individuals with gfr  60 ml / min/1.73
m aged  35 years was 10.2% and 8.7% , respectively , in the previous korean population .
besides the different age criteria , the populations of the previous and current study are quite different ; the previous study was designed by the researcher group considering age , gender , and city factors not using the knhanes sample data .
although the absolute values are different , the important point in common is that a large number of people have albuminuria before gfr decreases to < 60 ml / min/1.73 m ( 85.3% and 87.7% of the albuminuria cases did not have decreased gfr in the previous and current study , respectively ) . as shown in table 3
, test strips did not detect albuminuria in 81.5% of cases . at present , laboratory tests for albuminuria are not routinely performed during regular physical examinations in korea .
the prevalence of ckd in men and women was 6.9% and 9.1% , respectively ( p < 0.001 ) . besides gender itself , age distribution , frequency of obesity
( bmi  25 ) , and concurrent chronic diseases , including dm , hypertension , and dyslipidemia , were different according to gender .
thus , the risk of ckd is higher in women than men ( or , 1.354 ; p < 0.001 ) , and the difference seems to be caused by the susceptibility to albuminuria ( or , 1.416 ; p < 0.001 ) rather than decreased gfr ( or , 1.057 ; p = 0.683 ) .
when gfr was estimated using the mdrd study equation , the increased risks of gfr < 60 ml / min/1.73
m in women were observed in previous studies : or , 3.16 ( p < 0.001 ) using knhanes iii and iv-1 ; frequencies of 3.4% , 9.7% , 10.2% , and 4.6% in women , and 1.0% , 5.4% , 3.1% , and 2.6% were seen in men through knhanes i - iv .
there seemed to be no difference in acr according to gender in the previous study ( 10.1% and 10.3% in women and men , respectively ) .
a similar observation was reported for proteinuria by gender ( frequencies of 3.3% , 2.3% , 1.4% , and 1.9% in women , and 3.1% , 3.0% , 2.8% , and 2.2% in men through knhanes
direct comparison is difficult due to the difference in the designs of study populations   and laboratory test methods using dipstick proteinuria and acr .
increasing age and obesity ( bmi  25 ) correlated significantly with ckd , as shown in table 6 , which agreed with previous studies [ 11 - 13 ] .
hypertension and dm are both major risk factors and consequences of ckd [ 21 - 23 ] . concurrent chronic diseases such as dm and hypertension increased the risk of ckd consistently [ 11 - 13 ]
. diabetic patients are susceptible to glomerular disease and hypertensive patients to renal vascular disease .
since the prevalence of dm was higher in men than women , with the opposite for prevalence of ckd , the or of dm to ckd in men was higher than women , as shown in table 6 .
moreover , dm was correlated with increased acr rather than decreased gfr in this study . since increased acr appeared at an earlier age in women than men , and decreased gfr
was preceded by increased acr , the difference between ors to gfr < 60 ml / min/1.73 m and acr  30 mg / g in hypertensive women was greater than hypertensive men . on the other hand ,
limited availability of direct ldl - c measurement , unstandardized laboratory assay methods for hdl - c , and lack of a uniform definition of dyslipidemia between the studies made it difficult to evaluate their associations .
the major limitation of this study is the lack of the evaluation for chronicity assessment and use of single measurements for laboratory tests due to the cross - sectional data characteristics . according to the definition of ckd by the kdigo guideline
the rationale for defining chronicity is to differentiate ckd from acute kidney diseases , which may require different interventions and have different etiologies and outcomes .
in addition , there is still the discrepancy between measured and estimated gfr using ckd - epi equations .
gfr estimation using equations is convenient , but measurement of gfr should be considered to diagnose a specific patient .
finally , association analysis could not provide conclusive causal relationships due to the study characteristics .
however , the representative features of the knhanes sample data can not be overlooked . in conclusion ,
the prevalence of ckd using estimated gfr by the ckd - epi equation and acr for albuminuria measurement was 7.9% in the knhanes samples of 2011 and 2012 in korean adults aged  19 .
the prevalence of albuminuria ( acr  30 mg / g ) before decline in gfr ( gfr  60 ml / min/1.73 m ) was 5.7% . despite kdigo guidelines to prevent or delay progression of ckd in its early stages , implementation remains difficult due to practical limitations .
the failure to recognize ckd in its early stage may result in complications such as premature rrt .
thus , urinalysis to detect albumin should be strongly recommended for patients with higher risk of ckd and cvd . as there is a consensus about the risk of ckd with dm and hypertension , regular albuminuria testing for at least these patients to detect kidney disease at an early stage
1 . the prevalence of chronic kidney disease ( ckd ) was estimated to be 7.9% in the korea national health and nutrition examination survey samples of 2011 and 2012 in korean adults aged  19 .
early identification of ckd paired with appropriate management and earlier referral to specialty kidney services results in economic and clinical benefits .
the majority of ckd patients have albuminuria prior to a decrease in glomerular filtration rate .
4 . regular laboratory tests for albuminuria in the high - risk group , especially for hypertensive or diabetes mellitus patients , should contribute to early detection of ckd .
 background / aimsan updated chronic kidney disease ( ckd ) definition and classification were proposed by kidney disease : improving global outcomes ( kdigo ) , with adoption of a new equation to estimate glomerular filtration rate ( gfr ) and albuminuria to evaluate kidney structural damage . 
 this study was performed to estimate the prevalence of ckd in the korean adult population as defined and classified by the kdigo guidelines.methodscross-sectional samples of the fifth korean national health and nutrition examination survey for 2011 to 2012 were examined for adults aged  19 years . 
 ckd prevalence was determined based on decreased gfr and albuminuria . 
 the gfr was estimated using the ckd epidemiology collaboration creatinine equation , and albuminuria was evaluated using the albumin - to - creatinine ratio ( acr ) in spot urine.resultsof the 16,576 subjects participating in the survey , 10,636 ( 4,758 men , 5,878 women ) were included in the present study . 
 the prevalence of ckd was estimated as 7.9% ( 7.8% in 2011 and 8.0% in 2012 , p = 0.770 ) . 
 the prevalence of low , moderately increased , high , and very high ckd risk prognosis was 92.0% , 6.3% , 1.1% , and 0.6% , respectively . 
 the prevalence of albuminuria ( acr  30 mg / g ) in individuals with gfr  60 ml 
 / min/1.73 m2 has reached 5.7% . 
 the odds ratios of hypertension and diabetes to ckd were 3.4 and 3.1 in men , and 2.9 and 2.0 in women ( all p < 0.001 ) , respectively.conclusionsa large percentage of ckd patients had albuminuria prior to a decrease in gfr . 
 regular laboratory tests for albuminuria for the high - risk group , and especially for hypertensive or diabetic patients , might improve detection of ckd at an early stage . 