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Indicator Details — Emerging Topics: Adjusted Risk of Progression to ESRD by Tertiles of Estimated Dietary Acid Loada,b,c,d
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a Adjusting for demographic factors: p-trend of tertiles= 0.03*

b Adjusting for demographic + nutritional factors: p-trend of tertiles= 0.04*

c Adjusting for demographic +nutritional +clinical factors: p-trend of tertiles= 0.06

d Adjusting for demographic +nutritional +clinical + kidney functional damage factors: p-trend of tertiles= 0.05*

*Statistically significant

Diet affects the acid-base status and emerging data suggest that dietary patterns may influence the risk of end-stage renal disease (ESRD) in individuals with pre-existing CKD. 20.9% of National Health and Nutrition Examination Survey III (NHANES III) participants with CKD developed ESRD over a median follow-up of 14.2 years. 
Chart Explanation: With adjustment for demographics, participants in the highest dietary acid load (DAL) tertile showed an increased relative hazard of ESRD compared with the referent group (lowest tertile) (RH 4.13; 95% CI 2.09-7.81). Further adjustment for nutritional factors of body surface area, total caloric intake per day, serum bicarbonate, and protein intake attenuated the risk of ESRD (RH 3.45; 95% CI 1.83-6.52). The risk of ESRD was further attenuated when adjusted for clinical risk factors of diabetes and hypertension (RH 2.73; 95% CI 1.44-5.18). DAL levels in the highest and middle tertiles remained associated with a higher risk of ESRD (RH 3.04; 95% CI 1.58-5.86 and 1.81; 95% CI 0.89-3.68, respectively) as compared to the lowest tertile when fully adjusted for demographics, nutritional and clinical factors, kidney function/damage and accounting for intervening mortality events (via a competing risk model).
The National Health and Nutrition Examination Survey III (NHANES III) is the third cycle of today’s continuous NHANES. NHANES III was conducted from 1988-1994 in 81 United States counties. This survey focused on oversampling many groups within the U.S. population, including young children and older persons.  eGFR was calculated according to the CKD-EPI formula for serum creatinine (Levey et al. 2009). Dietary acid load was calculated using the 24-hour dietary recall questionnaire and the Remer and Manz estimated dietary acid load formula (Remer and Manz. 1995). NHANES III data was linked to follow-up data from the Medicare ESRD Registry and National Death Index through 2006. 

Covariates hypothesized to contribute to CKD progression were included in the adjusted models if they were associated with progression of CKD in univariate analyses (p<0.20). There was an indication of collinearity of moderate strength between age and PIR (Variance Inflation Factor=3.26, tolerance=0.31, condition index=14.43). Therefore, the data was analyzed by excluding the socioeconomic position factors (Poverty income ratio and education level). Models were adjusted for demographic factors (age, sex, and race/ethnicity), nutritional factors (body surface area, total caloric intake per day, serum bicarbonate, and protein intake), clinical factors (diabetes and hypertension), and kidney function/damage markers (eGFR and albuminuria).
Description of MeasureRisk of Progression to ESRD for Tertiles of Estimated Dietary Acid Load
Data SourceNational Health and Nutrition Examination Survey III (NHANES III)
Type of Data SourcePublic
Health Care System DataNo
Regional or National?National
Demographic GroupNon-pregnant adults 20 years of age or greater with no missing dietary intake data and eGFR of 15 - 60 ml/min/1.73 m²
NumeratorESRD or death
DenominatorNHANES III participants with serum creatinine, urine albumin, urine creatinine, and 24-hour dietary recall questionnaire data. 
Definition of CKDEstimated GFR of 15 - 60 mL/min per 1.73 m2
Glomerular filtration rateEstimated, CKD-EPI equation
Primary Data Source IndicatorSerum creatinine
Primary Indicator Method of MeasurementLaboratory blood sample
Secondary Data Source IndicatorDietary Acid Load
Secondary Indicator Method of Measurement24-hour dietary recall questionnaire
Frequency of Measurement (Primary)Once (cross-sectional)
U.S. Region Covered by Primary VariableAll
Period Currently Available2006
Pending DataNone
Additional Data Items of InterestAdjustment variables of interest (age, gender, race/ethnicity, BSA, total caloric intake per day, serum bicarbonate, protein intake, diabetes, hypertension, eGFR, albuminuria)
Limitations of IndicatorAlbuminuria and kidney function can only be assessed from a one-time cross-sectional measurement, leading to overestimation of CKD prevalence; diet reported from 24-hour diet recall may not be representative 
Analytical ConsiderationsAs with all cohort studies, selection bias and possible confounding
References and Sources:

Suggested Citation:
Centers for Disease Control and Prevention. Chronic Kidney Disease Surveillance System—United States.
website. http://www.cdc.gov/ckd