The authors have declared that no competing interests exist.
Conceived and designed the experiments: F. Hadaegh MT. Analyzed the data: MH DK RM. Wrote the paper: F. Hadaegh MT RM. Involved in acquisition of analysis data files from cohort database: MH F. Hadaegh RM. Contributed to interpretation of results: F. Hadaegh MT F. Hosseinpanah RM BY AH-N FA. Critically reviewed drafts of the manuscript and made comments to improve clarity: F. Hadaegh MT RM.
To examine, the predictors of incident chronic kidney disease (CKD) in a community-based cohort of Middle East population, during a mean follow-up of 9.9 years. In a sample of 3313 non-CKD Iranian adults ≥20 years the estimated glomerular filtration rate (eGFR) was calculated at baseline and at three year intervals during three consecutive phases. The eGFR <60 mL/min/1.73 m2 was defined as CKD. Multivariate Logistic regression analysis was used to determine the independent variables associated with incident CKD. The incidence density rates of CKD were 285.3 and 132.6 per 10,000 person-year, among women and men, respectively. Female gender per se was associated with higher risk of CKD, compared with males. Among women, age, eGFR, known diabetes, being single or divorced/widowed, hypertension (marginally significant) and current smoking were independent risk factors for CKD; however the intermediate degree of education and family history of diabetes decreased the risk by 40% (P<0.05). Among male subjects, independent predictors of developing CKD included aging and hypertension (with significantly higher risk than in women, P for interaction<0.05), eGFR, new diagnosed diabetes, high normal blood pressure; abdominal obesity decreased the risk of CKD about 30% which was marginally significant. In the Iranian population,>2% of individuals develops CKD each year. Our findings confirmed that sex- specific risk predictors should be considered in primary prevention for incident CKD.
There is a rising prevalence and incidence of chronic kidney failure (CKD), with poor outcomes and high cost in the world
The prevalence of CKD among the Iranian population is known to be high
In brief, the TLGS is a large scale, long term, community-based prospective study performed on a representative sample of residents of district No. 13 of Tehran, capital of Iran
CKD; chronic kidney disease.
Subjects were interviewed privately, by trained interviewers, using pretested questionnaires. Initially, information on demographics, education, smoking status, medical and drug history was collected. Anthropometric measures including weight, height, waist circumference (WC) was measured according to a standard protocol
Fasting and 2-hours plasma glucose (FPG and 2-hPG respectively) were measured by enzymatic colorimetric glucose oxidase method; both inter-and intra-assay coefficient of variations (CV) were less than 2.2%. Total cholesterol (TC) and triglycerides (TG) were assayed using the enzymatic calorimetric method with cholesterol esterase- cholesterol oxidase and glycerol phosphate oxidase, respectively. For both total and HDL-Cholesterol, intra-and inter-assay CVs were 0.5 and 2% respectively. Intra and inter-assay CVs were 0.6 and 1.6% for TG respectively.
Serum creatinine (cr) levels were assayed by kinetic colorimetric Jaffe. The sensitivity of the assay was 0.2 mg/dL (range, 18–1330 µmol/L (0.2–15 mg/dL). Reference intervals according to manufacturer’s recommendation were 53–97 µmol/L (0.6–1.1 mg/dL) and 80–115 µmol/L (0.9–1.3 mg/dL) in women and men respectively. Both intra-assay and inter-assay CVs were less than 3.1% in both baseline and follow-up phases. All biochemical assays were performed using commercial kits (Pars Azmoon Inc., Tehran, Iran) by a Selectra 2 auto analyzer (Vital Scientific, Spankeren, The Netherlands). Assay performance was monitored after every 25 tests using lyophilized serum controls in normal and pathologic ranges and all samples were analyzed when internal quality control met the standard acceptable criteria.
According to the Kidney Disease Outcome Quality Initiative guidelines, chronic kidney disease is defined as either kidney damage or Glomerular Filtration Rate (GFR) <60 mL/min/1.73 m2 for >3 months
Abbreviated MDRD study equation:
In this equation, eGFR (estimated GFR) is expressed as mL/min per 1.73 m2 and serum creatinine (Scr) is expressed as mg/dL
Incident CKD was considered an eGFR below than 60 mL/min/1.73 m2 occurring at any time during the follow-up period. This corresponds to stage 3 to stage 5 CKD based on the Kidney Disease Outcomes and Quality Initiative guidelines.
Body mass index was categorized in to 3 groups of <25 kg/m2 (reference), 25 to <30 kg/m2 (overweight), and ≥30 kg/m2 (obese). Abnormal waist circumference was set at ≥90 cm for both genders, as defined for Iranian populations
Dyslipidemia was defined as serum triglycerides of ≥2.26 Mmol/l or cholesterol of ≥6.19 Mmol/l and included subjects taking lipid lowering medications
Mean (standard deviation: SD) values for continuous and frequencies (%) for categorical variables of the baseline characteristics are given for participants with and without incident CKDs3-5. Since FPG, 2h-PG and TG had skewed distribution they are shown as median (interquartile range). Comparison of baseline characteristics between participants with and without incident CKDs3-5 was done by student’s t-test for continuous variables, chi-square test for categorical variables and Mann-Whitney test for skewed variables.
To reduce selection bias
The association of different categorical risk factors with incident CKDs3-5 was assessed by calculating multivariate adjusted odds ratios (ORs) with 95% CI using binary logistic regression analysis. For risk factors with more than 2 categories the first category was considered as the reference group. Each candidate predictor (age categories, eGFR categories, hypertension categories, diabetes groups, dyslipidemia, smoking status, history of CVD, family history of diabetes, educational levels, marital status,general and abdominal obesity) with a p-value less than 0.2 in the initial univariable analysis was included in the multivariable analysis. The probability of participation in follow-up was used as a propensity score, which added to the logistic models as a covariate. This probability was associated with incident CKDs3-5 in the multivariate model among women (p<0.001). However, we entered the propensity score in models running among men and whole population as well. The selection bias, therefore, probably did not affect our estimations.
In multivariate analysis, the effect modification of gender on the relation between other covariates and CKDs3-5 outcome were tested by entering the interaction terms (covariate × gender) in the model; there were significant effect modification of gender on all age groups (all Ps <0.05), new diagnosed diabetes (P<0.001), high normal blood pressure (P = 0.05) and hypertension (P = 0.001). Hence, we stratified our analysis by gender. Also, for our findings to be comparable to other studies, we showed our data analyses in the whole population as well. All P-values were two-tailed. P-value ≤0.05 being considered statistically significant. Statistical analyses were performed using SPSS program (SPSS Inc., Chicago, IL, USA; Version 15).
As shown in
Men | Women | ||||||
Non-followed up (N = 837) | Followed up (N = 1454) | P-V | Non- Followed up (N = 932) | Followed up(N = 1859) | P-V | ||
Age(years) | 41.46(15.78) | 41.35(13.43) | .86 | 36.24(12.95) | 38.33(11.99) | <.001 | |
eGFR(ml/min/1.73m2) | 76.26(10.11) | 75.69(10.04) | .19 | 74.56(9.86) | 72.99(9.13) | <.001 | |
FPG(mmol)/l | 5.05(4.72–5.50) | 5.05(4.72–5.44) | .24 | 4.88(4.55–5.27) | 4.88(4.61–5.27) | .68 | |
2-hPG (mmol)/l | 5.49(4.44–6.73) | 5.55(4.49–6.77) | .79 | 5.83(4.91–7.05) | 5.88(4.94–7.05) | .85 | |
TC(mmol)/l | 5.12(1.13) | 5.28(1.13) | .001 | 5.21(1.20) | 5.34(1.22) | .008 | |
TG(mmol)/l | 1.59(1.08–2.35) | 1.77(1.23–2.52) | <.001 | 1.39(0.96–2.07) | 1.40(0.97–2.14) | .25 | |
SBP(mmHg) | 119.68(19.43) | 119.06(16.69) | .44 | 115.06(116.83) | 115.46(16.98) | .56 | |
DBP(mmHg) | 77.15(11.40) | 77.75(10.67) | .22 | 76.65(10.04) | 76.81(9.91) | .68 | |
Waist(cm) | 87.16(11.80) | 87.97(11.21) | .10 | 84.77(13.56) | 85.90(12.25) | .04 | |
BMI(kg/m2) | 25.34(4.25) | 25.61(4.06) | .13 | 26.82(5.48) | 27.21(4.83) | .07 | |
DM Drug (%) | 4.1 | 1.7 | .001 | 2.9 | 2.5 | .53 | |
Lipid Drug (%) | 1.6 | 1.1 | .44 | 2.7 | 3.0 | .81 | |
HTN Drug (%) | 4.3 | 2.9 | .09 | 4.5 | 5.4 | .31 | |
Marital status (%) | .008 | <.001 | |||||
Married | 75.4 | 80.8 | 73.9 | 84.1 | |||
Divorced/Widowed | 0.6 | 0.6 | 6.1 | 5.4 | |||
Single | 24.0 | 18.6 | 20.0 | 10.5 | |||
HCVD (%) | 6.4 | 3.7 | .005 | 2.0 | 2.1 | .89 | |
FHDM (%) | 24.6 | 26.1 | .45 | 26.8 | 28.2 | .47 | |
Smoking (%) | .15 | .09 | |||||
Never | 54.1 | 58.1 | 92.2 | 94.3 | |||
Past | 13.6 | 13.3 | 2.3 | 1.8 | |||
Current | 32.4 | 28.7 | 5.5 | 3.8 | |||
Education Level (%) | .31 | .21 | |||||
Higher than diploma | 19.4 | 19.0 | 11.3 | 9.8 | |||
Diploma/Cycle | 56.2 | 59.2 | 59.7 | 58.5 | |||
Illiterate/Primary School | 24.4 | 21.8 | 29.0 | 31.8 |
TLGS; Tehran lipid and glucose study,CKD; chronic kidney disease, P-V; p-value, eGFR; estimated glomerular filtration rate, FPG; fasting plasma glucose, 2-hPG; 2-hours plasma glucose,TC; total cholesterol, TG; triglyceride, SBP; systolic blood pressure, DBP; diastolic blood pressure, BMI; body mass index, DM; diabetes mellitus, HTN; hypertension, HCVD, history of cardiovascular disease,FHDM; family history of diabetes mellitus.
Men | Women | |||||
Non-CKD (N = 1248) | CKD(N = 206) | P-V | Non-CKD (N = 1342) | CKD(N = 517) | P-V | |
Age(years) | 39.28(12.56) | 53.87(11.64) | <.001 | 35.52(10.67) | 45.63(12.17) | <.001 |
eGFR(ml/min/1.73m2) | 76.99(9.83) | 67.78(7.34) | <.001 | 74.97(9.28) | 67.84(6.31) | <.001 |
FPG(mmol)/l | 4.99(4.66–5.38) | 5.33(4.88–5.97) | <.001 | 4.88(4.55–5.22) | 4.99(4.66–5.49) | <.001 |
2-hPG (mmol)/l | 5.49(4.38–6.6) | 5.99(4.83–8.63) | <.001 | 5.83(4.88–6.94) | 6.05(5.05–7.55) | .008 |
TC(mmol)/l | 5.24(1.13) | 5.54(1.06) | <.001 | 5.2(1.15) | 5.71(1.35) | <.001 |
TG(mmol)/l | 1.75(1.2–2.51) | 1.91(1.4–2.56) | .034 | 1.31(0.92–2.02) | 1.68(1.12–2.39) | <.001 |
SBP(mmHg) | 117.3(15.1) | 129.5(21.56) | <.001 | 113.45(15.30) | 120.7(19.79) | <.001 |
DBP(mmHg) | 77.0(10.23) | 82.31(12.07) | <.001 | 75.92(9.5) | 79.14(10.57) | <.001 |
Waist(cm) | 87.5(11.18) | 90.6(11.04) | <.001 | 84.55(12.07) | 89.37(12.03) | <.001 |
BMI(kg/m2) | 25.52(4.08) | 26.18(3.88) | .035 | 26.74(4.8) | 28.4(4.6) | <.001 |
DM Drug (%) | 1.0 | 6.0 | <.001 | 1.3 | 5.7 | <.001 |
Lipid Drug (%) | 1.1 | 1.5 | .48 | 1.7 | 6.1 | <.001 |
HTN Drug (%) | 1.8 | 9.5 | <.001 | 3.3 | 10.8 | <.001 |
Marital status (%) | <.001 | <.001 | ||||
Married | 78.4 | 95.6 | 83.7 | 85.1 | ||
Divorced/Widowed | 0.5% | 1.5 | 3.2 | 11.0 | ||
Single | 21.2 | 2.9 | 13.1 | 3.9 | ||
HCVD (%) | 2.9 | 9.0 | <.001 | 1.4 | 3.9 | .002 |
FHDM (%) | 26.2 | 25.4 | .86 | 29.1 | 26.0 | .20 |
Smoking (%) | .69 | .008 | ||||
Never | 58.1 | 58.0 | 95.4 | 91.7 | ||
Past | 13.0 | 15.0 | 1.6 | 2.4 | ||
Current | 28.9 | 27.0 | 3.0 | 5.9 | ||
Education Level (%) | <.001 | <.001 | ||||
Higher than diploma | 19.8 | 14.1 | 10.1 | 8.9 | ||
Diploma/Cycle | 61.1 | 47.6 | 64.8 | 42.1 | ||
Illiterate/Primary School | 19.1 | 38.3 | 25.1 | 49.0 |
CKD; chronic kidney disease, P-V; p-value, eGFR; estimated glomerular filtration rate, FPG; fasting plasma glucose,2-hPG; 2-hours plasma glucose,TC; total cholesterol, TG; triglyceride, SBP, systolic blood pressure, DBP, diastolic blood pressure, BMI; body mass index, DM, diabetes mellitus, HTN; hypertension, HCVD, history of cardiovascular disease, FHDM; family history of diabetes mellitus.
Overall, 723 new cases CKDs3-5 were identified after a mean follow-up 9.9 years (minimum = 7.2, maximum = 12.3 years) resulting in a crude cumulative incidence of 21.8% (95%CI: 20.42–23.23). The corresponding cumulative incidence among women and men were 27.8% (517/1859), (95% CI: 25.77–29.85), and 14.2% (206/1454), (95% CI: 12.38–15.96), respectively. The incidence density rate of CKDs3-5 among the whole population was 214.82 (95% CI 199.72–231.07) per 10,000 person/years; and corresponding incidence rates among women and men were 285.3 (95% CI 261.8–311.0) and 132.6 (95% CI 115.7–152.0), respectively.
Men | Women | |||
Odds ratio (CI) | p-value | Odds ratio (CI) | p-value | |
Age(years) | ||||
20–34 | Reference | Reference | ||
35–49 | 3.36 (1.41–8.02) | 0.01 | 1.17(0.83–1.63) | 0.37 |
50–64 | 10.85(4.44–26.55) | <0.001 | 2.54(1.54–4.20) | <0.001 |
≥65 | 13.47(4.72–38.47) | <0.001 | 2.76(1.15–6.63) | 0.02 |
eGFR(ml/min/1.73m2) | ||||
<75 | Reference | Reference | ||
≥75 & <90 | 0.27(0.16–0.43) | <0.001 | 0.39(0.27–0.56) | <0.001 |
≥90 | 0.07(0.01–0.52) | 0.01 | 0.25(0.07–0.86) | 0.03 |
Diabetes Group | ||||
None | Reference | Reference | ||
IGT/IFG | 1.04(0.66–1.64) | 0.88 | 0.98(0.70–1.36) | 0.89 |
New diagnosedDM | 2.48(1.37–4.51) | 0.003 | 0.98(0.58–1.66) | 0.94 |
Known DM | 2.17 (0.68–6.90) | 0.19 | 6.20 (2.68–14.36) | <0.001 |
Marital status | ||||
Married | Reference | Reference | ||
Divorced/Widowed | 1.23(0.16–9.70) | 0.85 | 2.94(1.63–5.29) | <0.001 |
Single | 0.89(0.30–2.65) | 0.84 | 3.08(1.24–7.64) | 0.02 |
HCVD | ||||
No | Reference | Reference | ||
Yes | 0.88(0.40–1.94) | 0.75 | 1.44(0.67–3.10) | 0.35 |
Education Level | ||||
Higher than diploma | Reference | Reference | ||
Diploma/Cycle | 1.13(0.68–1.88) | 0.65 | 0.62(0.41–0.94) | 0.03 |
Illiterate/Primary School | 0.95(0.53–1.68) | 0.85 | 0.80(0.50–1.28) | 0.34 |
Hypertension | ||||
Optimal | Reference | Reference | ||
Normal | 1.11(0.65–1.88) | 0.70 | 0.94(0.68–1.29) | 0.69 |
High normal | 1.74(0.99–3.04) | 0.05 | 1.23(0.81–1.87) | 0.32 |
Hypertension | 2.20(1.38–3.52) | 0.001 | 1.40(0.96–2.06) | 0.08 |
Dyslipidemia | ||||
No | Reference | Reference | ||
Yes | 1.38(0.93–2.03) | 0.11 | 0.79(0.60–1.05) | 0.11 |
Abdominal Obesity | ||||
No | Reference | Reference | ||
Yes | 0.70(0.48–1.04) | 0.08 | 0.98(0.71–1.35) | 0.91 |
BMI(kg/m2 ) | ||||
<25 | Not Applicable* | Reference | ||
≥25 & <30 | 1.26(0.91–1.74) | 0.17 | ||
≥30 | 1.39(0.91–2.10) | 0.12 | ||
Smoking | ||||
Never | Not Applicable* | Reference | ||
Past | 1.67(0.66–4.22) | 0.28 | ||
Current | 5.74(2.71–12.15) | <0.001 | ||
FHDM | ||||
No | Not Applicable* | Reference | ||
Yes | 0.63(0.48–0.84) | 0.002 |
Odds ratios were obtained by multivariate logistic regression analysis. Dyslipidemia; TG of ≥2.26 Mmol/l or TC of ≥6.19 Mmol/l or subjects taking lipid lowering medications. Abdominal Obesity; waist circumference≥90 in both genders, TLGS; Tehran lipid and Glucose Study, eGFR; estimated glomerular filtration rate,IGT; Impaired glucose test, IFG; Impaired fast glucose, DM, diabetes, HCVD, history of cardiovascular disease, FHDM; family history of diabetes mellitus, BMI; Body mass index.* Had p-values >0.2 in the initial univariable analysis and were not included in the multivariable analysis.
Among male subjects, adjusted predictors of developing CKD included aging,hypertension,high normal BP (which had significantly higher risk than in women), eGFR, new diagnosed diabetes [2.48(1.37–4.51];interestingly abdominal obesity decreased the risk of CKDs3-5 about 30% which was marginally significant.
Finally, in the whole population, in which the female gender per se was associated with more than tripling risk of CKD compared with men(3.17,95% CI 2.44–4.12), age, eGFR, known diabetes,current smoking and hypertension were independent predictors.(
Total | ||
Odds ratio(CI) | p-value | |
Sex | ||
Male | Reference | |
Female | 3.17(2.44–4.12) | <0.001 |
Age(years) | ||
20–34 | Reference | |
35–49 | 1.61(1.21–2.14) | 0.001 |
50–64 | 5.12(3.59–7.28) | <0.001 |
≥65 | 7.67(4.44–13.24) | <0.001 |
eGFR(ml/min/1.73m2) | ||
<75 | Reference | |
≥75 &<90 | 0.29(0.22–0.38) | <0.001 |
≥90 | 0.11(0.04–0.30) | <0.001 |
Diabetes Group | ||
None | Reference | |
IGT/IFG | 0.95(0.73–1.24) | 0.72 |
New diagnosed DM | 1.21(0.81–1.80) | 0.36 |
Known DM | 2.89(1.41–5.89) | 0.004 |
Marital status | ||
Married | Reference | |
Divorced/Widowed | 1.28(0.80–2.05) | 0.30 |
Single | 0.68(0.38–1.22) | 0.20 |
HCVD | ||
No | Reference | |
Yes | 1.34(0.76–2.35) | 0.31 |
Education Level | ||
Higher than diploma | Reference | |
Diploma/Cycle | 0.81(0.59–1.12) | 0.20 |
Illiterate/Primary School | 0.81(0.57–1.16) | 0.26 |
Hypertension | ||
Optimal | Reference | |
Normal | 0.89(0.68–1.16) | 0.38 |
High normal | 1.25(0.90–1.72) | 0.19 |
Hypertension | 1.43(1.08–1.91) | 0.01 |
Dyslipidemia | ||
No | Reference | |
Yes | 0.95(0.75–1.20) | 0.65 |
Abdominal Obesity | ||
No | Reference | |
Yes | 0.85(0.65–1.11) | 0.23 |
BMI(kg/m2 ) | ||
<25 | Reference | |
> = 25 &<30 | 1.12(0.86–1.47) | 0.39 |
> = 30 | 1.1(0.77–1.57) | 0.60 |
Smoking | ||
Never | Reference | |
Past | 0.81(0.52–1.27) | 0.36 |
Current | 1.45(0.99–2.13) | 0.06 |
Odds ratios were obtained by multivariate logistic regression analysis.TLGS; Tehran lipid and Glucose Study, eGFR; estimated glomerular filtration rate, IGT; Impaired glucose test, IFG; Impaired fast glucose, DM, diabetes, HTN; hypertension, HCVD, history of cardiovascular disease, BMI; Body mass index. Dyslipidemia; TG of ≥2.26 Mmol/l or TC of ≥6.19 Mmol/l or subjects taking lipid lowering medications. Abdominal Obesity; waist circumference≥90 in both genders.
According to the results of the present study, in the Iranian population, aged 20 years and over, more than 2% of individuals developed CKDs3-5 each year, during 10 years follow-up. Among whole Iranian population, age, female gender, eGFR, known diabetes, current smoking and hypertension were found to be significant independent predictors for incident CKDs3-5. Additionally in sex stratified analysis among women, being single or divorced/widowed relative to being married were positive predictors, while intermediate degree of education and family history of diabetes were both negative predictors for incident CKDs3-5. Among men, newly diagnosed diabetes and high normal blood pressure was independent predictors.
In a combined cohort of 2 community-based studies, the Atherosclerosis Risk in Communities Study (ARIC) and the Cardiovascular Health Study (CHS), in a population aged 45 years or older, during a follow-up period of 9 years, 9.9% (ARIC) and 16.9% (CHS )developed incident CKDS3-S5,respectively
In a previous study of a Tehranian population, factors independently associated with CKD were age, female gender, BMI, high waist circumference, hypertension and dyslipidemia
Among risk factors analyzed in our study, aging was found as a significant predictor for CKD in both genders, as reported in other studies
We found known diabetes in the whole population and new diagnosed diabetes among men as significant risk factors for incident CKDs3-5. The lack of association between known diabetes and incident CKD among men might be related to lack of power, considering the wide confidence interval [2.144(0.667–6.888)]. Given the high prevalence and incidence of Type 2 diabetes and very low prevalence of Type 1 diabetes among an Iranian population, our results primarily reflect Type 2 diabetes
In the current study we did not find any independent risk for the general or central adiposity measure in prediction of incident CKD. In line with our findings, in the Framingham Heart Study, the significant association of general obesity with stage 3 CKD disappeared after considering known CVD risk factors
According to the national survey, approximately 25% Iranians, aged 25–64 years had hypertension, and among of whom, 25% were taking antihypertensive medications, of these treated subjects, only 24% had BP values <140/90 mmHg
Smoking arises as an important preventable renal risk factor based on studies highlighting a strong association of smoking and renal damage in men and women.Furthermore, some studies show favorable effects of smoking cessation on kidney function
Surprisingly, we found that among women, despite significant risk of known diabetes for incident CKD, the presence of family history of diabetes resulted in more than 35% lower risk for incident CKDs3-5 in multivariate analysis; findings which are speculated to be attributable to better dietary patterns among women with positive family history of diabetes. Furthermore, considering education as the socio-economic criteria of the study population we found Iranain women with intermediate degree of education (i.e. diploma or cycle) showed lower risk for CKDs3-5 compared to those with higher education.
In our study population we showed the lower mean eGFR in non-CKD 3-5 study population at the baseline, similar to the eGFR reported in two other populations based cohort studies conducted in Japan
Limitations of our study include first, we measured the baseline characteristics of the participants only once, and hence misclassification of potential risk factors such as blood pressure categories might attenuate our estimates. We based our diagnosis of CKD on a single estimate of eGFR, which we acknowledge tends to overestimate the incidence of kidney disease. Estimated GFR measurements exhibit a high degree of intra-individual variability and ideally require second measurements to accurately represent kidney function. The use of successive eGFR measurements, had they been available, would likely have reduced the incidence of CKDs3-4 but would not attenuated the association of the predictor variables with the outcome. Furthermore, most studies of CKD, epidemiologic and interventional, use single serum creatinine measurements. Second, we did not calibrate our serum creatinine measurements to the Cleveland Clinic, where the Modification of Diet in Renal Disease (MDRD) eGFR equation was derived; nor did we validate the MDRD eGFR equation in a local population, and this could also cause an overestimation in the incidence of CKDs3-5. Third, the differences between respondents (i.e. 15, 010 individuals) and non-respondents (i.e. 12,240 individuals ) in the TLGS cohort at baseline(1999–2001)
As strengths, this study includes the continued follow-up of the TLGS population and the actual measurement of CVD risk factors and laboratory parameters, rather than self-reported data. Furthermore, our cohort was not designed selectively for CKD events, which precludes possible referral or selection bias. Finally, we defined CKDS3-5 as outcome is our study, since the DMARD estimation formula, originated among persons with a baseline GFR <60ml/min/1.73 m2, is most precise for individuals at this stage of kidney function
To conclude, during 10 years follow-up, the cumulative incidence of CKDs3-5 among women and men were 27.8%and 14.2%, respectively. Age, hypertension and diabetes were found to be independent predictors of CKDs3-5 in both genders, with greater risks among men than women. Additionally, in males, high normal BP and, among females, current smoking and being single or divorced/widowed was a significant risk factor. Among females, family history of diabetes and intermediate degree of education were independently associated with a better renal function outcome, whereas in males abdominal obesity per se (marginally significant) had this association. Our findings confirm that sex- specific risk predictors should be considered in primary prevention for incident CKD among an Iranian population.
We express our appreciation to the participants of district-13 of Tehran for their enthusiastic support in this study. The authors thank N. Shiva for her assistance in language editing.