High prevalence of chronic kidney disease in Thailand
2007; Elsevier BV; Volume: 73; Issue: 4 Linguagem: Inglês
10.1038/sj.ki.5002701
ISSN1523-1755
AutoresVlado Perkovic, Alan Cass, Anushka Patel, Paibul Suriyawongpaisal, Federica Barzi, Steven J. Chadban, Stephen MacMahon, Bruce Neal,
Tópico(s)Global Health Care Issues
ResumoWe describe the prevalence of stage III and IV chronic kidney disease in Thailand from a representative sample of individuals aged 35 years and above using a stratified, multistage, cluster-sampling method. Population estimates were calculated by applying sampling weights from the 2000 Thai census. Glomerular filtration rates were estimated from serum creatinine using the Cockroft–Gault and the simplified Modification of Diet in Renal Disease (MDRD) formulae. The prevalence of stage III disease among individuals aged 35 years and above was estimated to be about 20% using the Cockroft–Gault formula and about 13% from the MDRD formula. Stage IV disease was present in about 0.9 and 0.6% of this population using the respective formulae. The highest prevalence rates were observed in less well-developed rural areas and the lowest in developed urban areas. The prevalence of chronic kidney disease was significantly higher than that reported in individuals over 40 years old from the United States for both stage III and IV disease and higher than the reported incidence in Taiwan and Australia. This high prevalence of chronic kidney disease in Thailand has obvious implications for the health of its citizens and for the allocation of health-care resources. We describe the prevalence of stage III and IV chronic kidney disease in Thailand from a representative sample of individuals aged 35 years and above using a stratified, multistage, cluster-sampling method. Population estimates were calculated by applying sampling weights from the 2000 Thai census. Glomerular filtration rates were estimated from serum creatinine using the Cockroft–Gault and the simplified Modification of Diet in Renal Disease (MDRD) formulae. The prevalence of stage III disease among individuals aged 35 years and above was estimated to be about 20% using the Cockroft–Gault formula and about 13% from the MDRD formula. Stage IV disease was present in about 0.9 and 0.6% of this population using the respective formulae. The highest prevalence rates were observed in less well-developed rural areas and the lowest in developed urban areas. The prevalence of chronic kidney disease was significantly higher than that reported in individuals over 40 years old from the United States for both stage III and IV disease and higher than the reported incidence in Taiwan and Australia. This high prevalence of chronic kidney disease in Thailand has obvious implications for the health of its citizens and for the allocation of health-care resources. The presence of chronic kidney disease (CKD) is associated with an increased risk of a multitude of adverse health outcomes, including end-stage kidney disease (ESKD) as well as a substantial reduction in life expectancy.1.Keith D.S. Nichols G.A. Gullion C.M. et al.Longitudinal follow-up and outcomes among a population with chronic kidney disease in a large managed care organization.Arch Intern Med. 2004; 164: 659-663Crossref PubMed Scopus (1366) Google Scholar,2.Go A.S. Chertow G.M. Fan D. et al.Chronic kidney disease and the risks of death, cardiovascular events, and hospitalization.N Engl J Med. 2004; 351: 1296-1305Crossref PubMed Scopus (8983) Google Scholar Therapeutic strategies to reduce the risk of ESKD and other complications in individuals with CKD are now available,3.Ruggenenti P. Perna A. Gherardi G. et al.Renoprotective properties of ACE-inhibition in non-diabetic nephropathies with non-nephrotic proteinuria.Lancet. 1999; 354: 359-364Abstract Full Text Full Text PDF PubMed Scopus (774) Google Scholar so early recognition and the institution of proven therapeutic strategies are important. Large population-representative surveys in the United States and Australia have reported the prevalence of CKD in these countries;4.Coresh J. Astor B.C. Greene T. et al.Prevalence of chronic kidney disease and decreased kidney function in the adult US population: Third National Health and Nutrition Examination Survey.Am J Kidney Dis. 2003; 41: 1-12Abstract Full Text Full Text PDF PubMed Scopus (2301) Google Scholar,5.Chadban S.J. Briganti E.M. Kerr P.G. et al.Prevalence of kidney damage in Australian adults: The AusDiab kidney study.J Am Soc Nephrol. 2003; 14: S131-S138Crossref PubMed Google Scholar however, much less information is available on prevalence rates elsewhere and, in particular, in developing regions.6.White S.L. Cass A. Atkins R.C. et al.Chronic kidney disease in the general population.Adv Chronic Kidney Dis. 2005; 12: 5-13Abstract Full Text Full Text PDF PubMed Scopus (75) Google Scholar Given the limited ability to afford dialysis and the rapidly increasing prevalence of conditions such as diabetes and hypertension that may predispose to the development of CKD, prevention strategies may be especially important in developing regions.7.InterASIA Collaborative Group Cardiovascular risk factor levels in urban and rural Thailand—The International Collaborative Study of Cardiovascular Disease in Asia (InterASIA).Eur J Cardiovasc Prev Rehabil. 2003; 10: 249-257Crossref PubMed Scopus (67) Google Scholar Thailand is a developing country in Asia with a population of more than 60 million people. The InterASIA study was designed and performed to estimate the prevalence of a variety of diseases in China and Thailand. In this study, we aim to estimate the prevalence of CKD among adults in Thailand. Of the 7909 Thai individuals aged 35 years and above invited to participate in InterASIA, 5303 (67%) took part in this study and creatinine measurements were available for 5146. The characteristics of the participants are shown in Table 1 and 2.Table 1Estimated mean levels and prevalence of participant characteristics overall and in rural compared to urban Thai adults aged 35 years and olderRuralUrbanP-valueAge (years)50.8 (1.4)50.2 (1.5)0.82Women (%)51.3 (6.6)53.1 (7.8)0.88Serum creatinine (mg per 100 ml)1.001 (0.016)0.986 (0.019)0.67Creatinine clearance (ml min−1)76.0 (1.6)79.6 (1.7)0.30GFR (ml min−1)77.1 (1.0)78.3 (1.0)0.55Hypertension (>140/90 mm Hg)14.6 (1.0)23.1 (1.1)<0.001SBP (mm Hg)119 (1.0)122 (1.2)0.06DBP (mm Hg)75 (0.5)78 (0.8)<0.001Current smoking (%)26.8 (4.4)20.8 (3.1)0.32Current alcohol consumption (%)35.6 (3.7)33.9 (3.2)0.76Diabetes (%)8.5 (0.8)11.9 (1.0)0.02Height (cm)157.1 (0.6)58.3 (0.8)0.40Weight (kg)58.3 (0.6)62.0 (0.8)0.001Body mass index (kg m−2)23.6 (0.2)24.7 (0.2)<0.001BSA, body surface area; DBP, diastolic blood pressure; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease; SBP, systolic blood pressure.Values are mean (s.e.) or percent (s.e.).Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula.P-values relate to comparisons between rural and urban populations. Open table in a new tab Table 2Baseline characteristics of participants according to regionUrbanRuralFactorNon-slumSlumDevelopedDevelopingUndevelopedP-valueAge (years)50.2 (1.7)50.2 (2.0)50.9 (1.9)50.6 (2.4)50.9 (3.9)0.99Women (%)53.1 (8.4)53.0 (10.2)50.6 (9.0)52.8 (12.0)60.8 (18)0.98Weight (kg)62.0 (0.9)61.5 (0.8)59.1 (0.8)56.2 (0.8)54.8 (2.4)<0.0001Height (cm)158.3 (1.0)157.7 (1.2)157.3 (1.1)156.6 (1.2)153.9 (1.7)0.25Body mass index (kg m−2)24.7 (0.2)24.7 (0.3)23.9 (0.3)22.9 (0.3)23.0 (0.9) 140/90 mm Hg)26.0 (2.5)26.7 (3.0)19.8 (2.7)13.0 (2.3)17.9 (5.7)0.01SBP (mm Hg)121.9 (1.3)121.6 (1.5)119.3 (1.3)116.7 (1.2)118.0 (3.0)0.026DBP (mm Hg)78.1 (0.8)78.7 (0.8)75.0 (0.7)73.2 (0.5)73.9 (1.3) 126 mg per 100 ml. Open table in a new tab BSA, body surface area; DBP, diastolic blood pressure; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease; SBP, systolic blood pressure. Values are mean (s.e.) or percent (s.e.). Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula. P-values relate to comparisons between rural and urban populations. BSA, body surface area; DBP, diastolic blood pressure; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease; SBP, systolic blood pressure. Values are mean (s.e.) or percent (s.e.). Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula. Diabetes defined as known diabetes or fasting plasma glucose >126 mg per 100 ml. Using the Cockroft–Gault formula, stage III CKD was estimated to be present in 20.1% (95% confidence interval (CI): 16.1–24.1) of Thai individuals aged more than 35 years and stage IV CKD in 0.94% (CI: 0.44–1.44%). This equates to approximately 5.0 million (CI: 4.5–5.5 million) and 230 000 (CI: 110 000–350 000) individuals with stage III and IV CKD, respectively. When the simplified Modification of Diet in Renal Disease (MDRD) formula was used, stage III CKD was present in 13.2% (CI: 10.6–15.8%) of the population and stage IV CKD in 0.61% (CI: 0.29–0.93%), equating to approximately 3.3 million (CI: 2.6–3.9 million) and 150 000 (CI: 70 000–230 000) individuals, respectively. The distribution of kidney function overall and in major population subgroups is shown in Table 3. A direct relationship was observed between age and CKD prevalence.Table 3Distribution of CKD stages overall and within subgroups of the Thai populationGFR prevalenceSubgroupNo. of participants% of Thai population>9060–8930–59<30Overall514610022.0 (1.5)64.0 (1.4)13.4 (1.3)0.6 (0.2)Gender Men201848.723.5 (2.0)64.3 (1.6)11.5 (1.5)0.7 (0.3) Women308151.320.6 (2.2)63.7 (2.1)15.1 (2.1)0.6 (0.2)Location Urban303532.322.4 (1.9)65.7 (1.3)11.2 (1.4)0.6 (0.2) Rural206467.721.8 (2.0)63.2 (1.9)14.4 (1.7)0.7 (0.2)Region Bangkok98910.922.5 (3.5)67.9 (2.3)9.6 (2.7)0.1 (0.1) North101522.125.4 (4.7)59.7 (3.3)13.6 (2.1)1.5 (0.5) Northeast107228.918.1 (2.1)64.9 (3.0)16.4 (3.3)0.5 (0.3) Central103325.223.6 (2.6)62.7 (1.4)13.3 (2.3)0.4 (0.3) South99012.921.7 (3.8)68.6 (2.6)9.4 (2.4)0.3 (0.2)Age (years) 35–44154840.835.0 (2.5)62.8 (2.4)2.1 (0.5)0.1 (0.1) 45–54136026.621.4 (2.0)70.3 (2.2)8.2 (0.9)0.1 (0.1) 55–64118117.28.7 (1.2)67.7 (2.3)22.6 (2.3)1.1 (0.4) 65+105715.43.5 (1.0)52.1 (2.9)41.8 (3.2)2.6 (0.9)Diabetes No447890.322.3 (1.6)65.4 (1.4)11.9 (1.2)0.4 (0.1) Yes6159.719.4 (3.3)50.7 (3.3)26.7 (2.8)3.0 (1.4)Hypertension No378378.824.3 (1.7)64.8 (1.6)10.4 (1.3)0.5 (0.1) Yes, no medication87314.617.0 (2.4)63.8 (2.4)18.2 (2.1)1.0 (0.5) Yes, medication4436.66.0 (2.5)54.5 (3.8)37.5 (3.7)2.0 (1.0)CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease.The simplified MDRD formula was used to estimate GFR. Open table in a new tab CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease. The simplified MDRD formula was used to estimate GFR. The proportion of individuals with CKD in population groups defined by their development status is shown in Figure 1 and their characteristics in Table 2. The prevalence of CKD was progressively higher across non-slum urban, slum urban, developed rural, developing rural, and undeveloped rural populations. Participants in less developed regions tended to be smaller and thinner but had higher serum creatinine levels (Table 2). The prevalence of hypertension was lower in less developed regions (P=0.01), and a lower prevalence of diabetes was observed than in more highly developed regions (P=0.03). The prevalence of CKD by development status was assessed separately for individuals with and without diabetes and hypertension (Figure 2). The prevalence of CKD decreased with increasing development status in people with and without hypertension and in those who did not have diabetes. No clear relationship was observed between development status and CKD prevalence for individuals with diabetes. The estimated prevalence rates of stage III and IV CKD in age- and sex-stratified subgroups of the United States, Taiwanese, and Australian populations have been published recently.4.Coresh J. Astor B.C. Greene T. et al.Prevalence of chronic kidney disease and decreased kidney function in the adult US population: Third National Health and Nutrition Examination Survey.Am J Kidney Dis. 2003; 41: 1-12Abstract Full Text Full Text PDF PubMed Scopus (2301) Google Scholar, 5.Chadban S.J. Briganti E.M. Kerr P.G. et al.Prevalence of kidney damage in Australian adults: The AusDiab kidney study.J Am Soc Nephrol. 2003; 14: S131-S138Crossref PubMed Google Scholar, 8.Hsu C.C. Hwang S.J. Wen C.P. et al.High prevalence and low awareness of CKD in Taiwan: a study on the relationship between serum creatinine and awareness from a nationally representative survey.Am J Kidney Dis. 2006; 48: 727-738Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar The creatinine measurements from the InterASIA study were standardized using a common laboratory for the US data to allow direct comparison of results for these two countries.9.Coresh J. Astor B.C. McQuillan G. et al.Calibration and random variation of the serum creatinine assay as critical elements of using equations to estimate glomerular filtration rate.Am J Kidney Dis. 2002; 39: 920-929Abstract Full Text Full Text PDF PubMed Scopus (619) Google Scholar Among individuals aged more than 40 years (Table 4), stage III CKD was twice as prevalent in Thailand compared to the United States according to both the Cockroft–Gault (25.5 vs 12.3%, P<0.001) and MDRD formulae (16.3 vs 8.1%, P<0.001). Stage III CKD was also substantially more prevalent in Thailand than in either Taiwan or Australia in age- and gender-matched subgroups (Table 4 and 5).Table 4Estimated prevalence of moderate (creatinine clearance or GFR <60) and severe (creatinine clearance or GFR <30) CKD in the Thai compared to the US populations according to age subgroupsP-valueAge subgroup (years)ThailandUSATaiwanUSATaiwanStage III CKD Cockroft–Gault 40–598.1 (0.9)0.8 (0.2)NA<0.001 60–6957.3 (3.1)10.1 (1.1)NA 7084.4 (2.7)46.1 (1.2)NA<0.001 All25.5 (0.6)12.3 (0.3)NA<0.001 MDRD 40–597.5 (0.8)1.8 (0.3)3.4 (2.0)<0.0010.17 60–6931.7 (2.2)7.6 (0.9)21.7 (3.4)<0.001 7047.1 (3.2)25.9 (1.1)31 (3.7)<0.001<0.0014 Overall16.3 (0.5)8.1 (0.3)NA<0.001Stage IV CKD Cockroft–Gault 40–59NA*The number of observations available in these categories was too few to allow a reliable estimate of prevalence.NA*The number of observations available in these categories was too few to allow a reliable estimate of prevalence.NA 60–692.6 (0.8)0.4 (0.2)NA 704.9 (1.4)3.1 (0.4)NA0.014 All >603.5 (0.1)1.8 (0.1)NA<0.001 MDRD 40–59NA*The number of observations available in these categories was too few to allow a reliable estimate of prevalence.NA*The number of observations available in these categories was too few to allow a reliable estimate of prevalence.NA 60–692.6 (0.8)0.5 (0.2)NA 701.2 (0.6)1.3 (0.3)NA0.88 All >602.1 (0.1)0.9 (0.1)NA0.001BSA, body surface area; CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease; NA, not available.Values are percent (s.e.).Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula.* The number of observations available in these categories was too few to allow a reliable estimate of prevalence. Open table in a new tab Table 5Estimated prevalence of stage III and IV CKD (calculated using the Cockroft–Gault formula) in the Thai and Australian populations according to gender and age subgroupsAge subgroup (years)ThailandAustraliaP-valueStage III CKD Male 45–6523.0 (3.0)1.8 (0.4) 6582.4 (3.3)51.8 (2.4)<0.001 Female 45–6513.3 (2.4)3.2 (0.7) 6574.5 (3.6)57.2 (2.9) 657.2 (2.8)1.5 (0.4)0.004 Female 45–650.5 (0.2)NANA >652.9 (1.1)1.9 (0.6)0.39BSA, body surface area; CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease.Values are percent (s.e.).Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula. Open table in a new tab BSA, body surface area; CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease; NA, not available. Values are percent (s.e.). Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula. BSA, body surface area; CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, Modification of Diet in Renal Disease. Values are percent (s.e.). Weighted using sampling factors from the 2000 Thai National Census population. Creatinine clearance calculated using the Cockroft–Gault formula and adjusted for a BSA of 1.73, GFR calculated using the simplified MDRD formula. Stage IV CKD was rare in individuals aged less than 60 years, so accurate prevalence rates could only be calculated for individuals aged more than 60 years (Table 4). Once again, stage IV CKD was more prevalent in Thailand than in the United States with both the Cockroft–Gault (3.5 vs 1.8%, P<0.001) and the MDRD formulae (2.1 vs 0.9%, P=0.001). A nonsignificant trend toward an increased prevalence of stage IV CKD was also observed when Thailand was compared to Australia (Table 5), and the difference was statistically significant in men but not in women. Data on stage IV CKD from Taiwan were not available. The population prevalence of an increased serum creatinine level (over 1.6 mg per 100 ml for males and 1.4 mg per 100 ml for females) by age group has been reported separately from the National Health and Nutrition Evaluation Survey (NHANES) data,10.Coresh J. Wei G.L. McQuillan G. et al.Prevalence of high blood pressure and elevated serum creatinine level in the United States: findings from the Third National Health and Nutrition Examination Survey (1988–1994).Arch Intern Med. 2001; 161: 1207-1216Crossref PubMed Scopus (495) Google Scholar and the comparative prevalence rates from Thailand and Australia are shown in Table 6. The prevalence of elevated creatinine was significantly higher in Thailand than in Australia and tended to be higher than that in the United States.Table 6Estimated prevalence of elevated creatinine (1.6 mg per 100 ml or greater in men, 1.4 mg per 100 ml or greater in women) in the Thai compared to the US and Australian populations according to age strataP-valueAge subgroupThailandUSAAustraliaUSAAustralia40–591.6 (0.3)1.3 (0.3)0.13 (0.05)0.48 6010.6 (0.6)7.3 (1.4)1.9 (0.3)0.057<0.001Values are percent (s.e.).Weighted using sampling factors from the 2000 Thai National Census population. Open table in a new tab Values are percent (s.e.). Weighted using sampling factors from the 2000 Thai National Census population. This study describes a remarkably high prevalence of CKD among individuals aged 35 years and above in Thailand. One in five individuals in this age group was found to have stage III or greater CKD, as defined by Kidney Disease Outcomes Quality Initiative (KDOQI),11.National Kidney Foundation K/DOQI Clinical Practice Guidelines for Chronic Kidney Disease: evaluation, classification, and stratification: Part 4. Definition and classification of stages of chronic kidney disease.Am J Kidney Dis. 2002; 39: S46-S75Abstract Full Text Full Text PDF Google Scholar when the Cockroft–Gault formula was used, and more than one in eight when the simplified MDRD formula was used. These figures do not include earlier stages of CKD defined by the presence of proteinuria, hematuria, or structural damage, as data on these parameters were not collected in this survey. As such, these figures underestimate the total prevalence of all stages of CKD as defined by KDOQI in this Asian population. Providing these estimates are accurate, the results have major implications for the citizens of Thailand and the health services responsible for their care. The prevalence of CKD as defined by reductions in glomerular filtration rate (GFR) was found to be much higher in Thailand than that either in the United States or in Australia. However, the difference is less marked when compared with the prevalence of CKD in Taiwan. Consistent with this, elevated serum creatinine concentrations were also found to be substantially more prevalent in Thailand than in the United States or Australia. Serum creatinine results were standardized,9.Coresh J. Astor B.C. McQuillan G. et al.Calibration and random variation of the serum creatinine assay as critical elements of using equations to estimate glomerular filtration rate.Am J Kidney Dis. 2002; 39: 920-929Abstract Full Text Full Text PDF PubMed Scopus (619) Google Scholar adding to the validity of the findings. Recent reports have found a high prevalence of CKD in other Asian countries; however, the prevalence of CKD is higher in Thailand than in mainland China12.Chen J. Wildman R.P. Gu D. et al.Prevalence of decreased kidney function in Chinese adults aged 35–74 years.Kidney Int. 2005; 68: 2837-2845Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar and Taiwan.8.Hsu C.C. Hwang S.J. Wen C.P. et al.High prevalence and low awareness of CKD in Taiwan: a study on the relationship between serum creatinine and awareness from a nationally representative survey.Am J Kidney Dis. 2006; 48: 727-738Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar The prevalence of CKD in mainland China varied significantly depending upon whether the Cockroft–Gault or MDRD method was used. For MDRD, the prevalence of stage III CKD was reported to be 2.53% compared to 13.2% in Thailand, and for the Cockroft–Gault method it was 19.6% compared to 20.1% in Thailand. The discrepancy between the MDRD- and Cockroft–Gault-based results is several fold greater in the mainland Chinese study than that reported in any other study, and it has not been clearly explained. A non-representative study from Okinawa in Japan13.Tanaka H. Shiohira Y. Uezu Y. et al.Metabolic syndrome and chronic kidney disease in Okinawa, Japan.Kidney Int. 2006; 69: 369-374Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar has also reported prevalence rates of 13% overall when the MDRD formula is used. The observed high prevalence of CKD in Thailand suggests that the number of people with stage V CKD who would potentially benefit from dialysis or transplantation might also be substantially higher than in western countries. The incidence of ESKD among universal health-care coverage beneficiaries in Thailand has been estimated to be between 101 and 304 per million population (p.m.p.) and although this range is quite broad, it is comparable to registry-based data from Australia (90–100 p.m.p.14.ANZDATAANZDATA Annual Report. ANZDATA, Adelaide, Australia2004Google Scholar), Europe (85–160 p.m.p.15.ERA-EDTAERA-EDTA Registry: ERA-EDTA Registry 2002 Annual Report. Academic Medical Center, Amsterdam, The Netherlands2002Google Scholar), and the United States (336 p.m.p.16.US Renal Data SystemUSRDS 2004 Annual Data Report: Atlas of End-Stage Renal Disease in the United States. National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD2004Google Scholar). The prevalence of CKD in Taiwan has been reported to be higher than that in the United States, and this country has the highest rates of ESKD in the world.8.Hsu C.C. Hwang S.J. Wen C.P. et al.High prevalence and low awareness of CKD in Taiwan: a study on the relationship between serum creatinine and awareness from a nationally representative survey.Am J Kidney Dis. 2006; 48: 727-738Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar Since many individuals in Thailand have limited access to dialysis due to a combination of equipment, personnel, and financial resource limitations,17.The National Health Security OfficeA Manual of National Health Security. A Security for Equitable and Standard Quality Health Care (in Thai). The National Health Security Office, Nonthaburi, Thailand2003: 2547Google Scholar,18.Cheowcharnwatana A. Limwatananonda C. Limwatananonda S. et al.Cost utility analysis of continuous hemodialysis and peritoneal dialysis in end stage renal diseases in Thailand (in Thai).J Nephrol Soc Thailand. 2003; 9: 158-169Google Scholar these findings suggest that there might be a large gap between need for and provision of renal replacement therapy (RRT) services. The magnitude of the difference in the observed prevalence of CKD between Thailand and previously reported rates from the United States and Australia is surprising. These findings raise the possibility of a large looming burden of individuals needing renal replacement therapy in Thailand over coming years and have profound public health implications. Many of the countries have limited health resources and are not currently able to provide dialysis therapy or transplantation for the majority of individuals with ESKD who may benefit from it.17.The National Health Security OfficeA Manual of National Health Security. A Security for Equitable and Standard Quality Health Care (in Thai). The National Health Security Office, Nonthaburi, Thailand2003: 2547Google Scholar,18.Cheowcharnwatana A. Limwatananonda C. Limwatananonda S. et al.Cost utility analysis of continuous hemodialysis and peritoneal dialysis in end stage renal diseases in Thailand (in Thai).J Nephrol Soc Thailand. 2003; 9: 158-169Google Scholar Thus, any increase in the prevalence of stage V CKD could rapidly translate into increased mortality and morbidity. The findings of this study may offer a potential window of opportunity for the use of therapeutic interventions known to reduce the rate of progression of CKD and therefore the incidence of ESKD and related diseases. These important findings raise questions about the methods used to measure and define kidney function and CKD. This study was carefully performed, with a high participation rate among invited individuals, careful collection of data, as well as appropriate collection, storage, and transport of blood samples. The serum creatinine measurements were all performed in a central standardized laboratory and were subsequently standardized in the National Institutes of Health (NIH) core laboratory to facilitate comparisons to NHANES data. Calculations of kidney function were undertaken using the most commonly used methods in clinical practice. As a result, it appears likely that the findings are real and are not due to methodological problems. It is possible that definitions of CKD based on calculations using the Cockroft–Gault and MDRD formulae are not reliable in Asian populations. This would not explain the differences in the prevalence of increased creatinine but may lead to the prevalence of CKD being overestimated in both this study and reports from China,12.Chen J. Wildman R.P. Gu D. et al.Prevalence of decreased kidney function in Chinese adults aged 35–74 years.Kidney Int. 2005; 68: 2837-2845Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar Taiwan,8.Hsu C.C. Hwang S.J. Wen C.P. et al.High prevalence and low awareness of CKD in Taiwan: a study on the relationship between serum creatinine and awareness from a nationally representative survey.Am J Kidney Dis. 2006; 48: 727-738Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar and Japan.13.Tanaka H. Shiohira Y. Uezu Y. et al.Metabolic syndrome and chronic kidney disease in Okinawa, Japan.Kidney Int. 2006; 69: 369-374Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar The accuracy of these formulae in Asian populations has been subject to little study and is therefore uncertain. One recent study performed in Chinese patients with CKD suggests that both formulae underestimate GFR in stage I CKD, and overestimate GFR in stage IV and V CKD.19.Zuo L. Ma Y.C. Zhou Y.H. et al.Application of GFR-estimating equations in Chinese patients with chronic kidney disease.Am J Kidney Dis. 2005; 45: 463-472Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar In stage III CKD, the MDRD formula tends to overestimate GFR, while the Cockroft–Gault formula was shown to reflect GFR measured by gold standard nuclear techniques.19.Zuo L. Ma Y.C. Zhou Y.H. et al.Application of GFR-estimating equations in Chinese patients with chronic kidney disease.Am J Kidney Dis. 2005; 45: 463-472Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar Of note, the prevalence of stage III CKD in Thailand was higher when estimated using the Cockroft–Gault formula (20.1%) than the MDRD formula (13.2%). It is therefore possible that the higher Cockroft–Gault-derived estimate of CKD prevalence may be more accurate. A similar study directly comparing estimated and measured GFR in a Thai population would be an important means of validating our results. A possible explanation for the high prevalence of CKD in Thailand is suggested by the observed variation according to the development status. It may have been expected that the highest prevalence of CKD would be observed in urban areas where the prevalence of diabetes and hypertension was greatest (Table 2), as the prevalence of CKD was higher in individuals with either hypertension or diabetes than those without these conditions (Figure 2). The reverse pattern was actually found (Figure 1), with an inverse relationship between the level of development of each region and the prevalence of CKD within it. Other factors such as endemic infection, sanitation, and access to perinatal and general health care may contribute to this observed difference.20.Cass A. Cunningham J. Hoy W. The relationship between the incidence of end-stage renal disease and markers of socioeconomic disadvantage.N S W Public Health Bull. 2002; 13: 147-151Crossref PubMed Scopus (15) Google Scholar,21.Cass A. Cunningham J. Snelling P. et al.End-stage renal disease in indigenous Australians: a disease of disadvantage.Ethn Dis. 2002; 12: 373-378PubMed Google Scholar This variation is clearly worthy of further study and more detailed analyses are underway. This study has some important limitations. GFR was estimated using formulae rather than being directly measured, and it was based on a single measurement of serum creatinine for each individual. It was restricted to individuals aged 35 years and above; therefore, the prevalence of CKD in younger individuals could not be estimated. Data regarding urinary albumin and protein excretion were not collected, so the prevalence of stage I and II CKD could not be estimated in this population. Finally, the formulae used to estimate GFR have not been validated in an Asian population, so it is not possible to say with certainty that the prevalence of CKD is truly as high as the results of this study suggest. The strengths of this study are its careful design and conduct, its excellent response rate, and the potential significance of the high reported prevalence of CKD. These important findings deserve further study, in particular, further investigation into possible mechanisms. More information on the health implications of CKD in Thailand and on the prevalence of CKD in other parts of the developing world is urgently required. A detailed description of the InterASIA study methods and procedures has been published elsewhere.7.InterASIA Collaborative Group Cardiovascular risk factor levels in urban and rural Thailand—The International Collaborative Study of Cardiovascular Disease in Asia (InterASIA).Eur J Cardiovasc Prev Rehabil. 2003; 10: 249-257Crossref PubMed Scopus (67) Google Scholar In brief, rural regions in Thailand were divided into developed, developing, and undeveloped areas, and urban regions were divided into slum and non-slum areas. Classification of the development status of urban and rural enumeration districts (EDs) is based on comprehensive development criteria defined by the Department of Community Development of the Thai Ministry of the Interior (http://www.porchor.moi.go.th/N2C/N2c4.html). Within each of these, a city block or village (in urban or rural areas, respectively) is made up of an ED. Within each ED, and using local government registers of households, the population aged 35 years and above was stratified into eight demographic groups, defined by age (35–44, 45–54, 55–64, and ≥65 years) and gender. Individuals were then sampled at random from each demographic group with the goal of recruiting a similar number of participants from each, but selecting no more than one individual from any household. The study was approved by an institutional review board, and all participants provided written informed consent. Trained study staff administered a structured questionnaire, performed a brief physical examination, and collected a fasting blood sample from each participant. The questionnaire sought information about basic sociodemographic variables, cardiovascular risk factors, history of cardiovascular diseases, current treatments, and behavioral characteristics. The physical examination included three measurements of blood pressure and a standard anthropometric assessment (height, weight, waist, and hip circumference). Biochemical analysis was performed on venous blood samples obtained after an 8-h overnight fast. Samples were stored immediately on ice, centrifuged, and separated on the day of collection. Sera were subsequently frozen and transported on dry ice to a central laboratory (Faculty of Medicine, Ramathibodi Hospital, Bangkok), where they were stored at –70 °C until they were analyzed using the Dimension RxLHM clinical chemistry system (Dade Behring Inc., Newark, Delaware, USA). To allow direct comparison to previously published data from the third wave of the NHANES in the US population,4.Coresh J. Astor B.C. Greene T. et al.Prevalence of chronic kidney disease and decreased kidney function in the adult US population: Third National Health and Nutrition Examination Survey.Am J Kidney Dis. 2003; 41: 1-12Abstract Full Text Full Text PDF PubMed Scopus (2301) Google Scholar serum creatinine measurements were standardized against stored sera at the NIH AASK core laboratory (Cleveland, OH, USA). A total of 200 serum samples across the range of observed results were sent to this laboratory, and the serum creatinine levels were remeasured. A regression formula was calculated for the two measurements, and this was used to adjust the original InterASIA serum creatinine measurements (adjusted creatinine=1.0617 × measured creatinine, R2=0.98). This adjustment did not significantly affect the results of the study. The level of kidney function for each individual was estimated using both the simplified MDRD and the Cockroft–Gault formulae. The simplified MDRD formula isGFR=186.3×creatinine-1.154×age-0.203(×0.742forwomen)(×1.21forAfricanAmericans) where creatinine is in mg per 100 ml and age is in years.22.Levey A. Greene T. Kusek J. et al.A simplified equation to predict glomerular filtration rate from serum creatinine.J Am Soc Nephrol. 2000; 11 (abstract A0828): 155AGoogle Scholar The Cockroft–Gault formula iscreatinine clearance (CrCl)=(140−age)/creatinineweight/72(×0.85 for women) where age is in years, serum creatinine in mg per 100 ml, and weight in kg.23.Cockcroft D. Gault M. Prediction of creatinine clearance from serum creatinine.Nephron. 1976; 16: 31-41Crossref PubMed Scopus (13102) Google Scholar The estimated creatinine clearance was then corrected for a body surface area (BSA) of 1.73 m2 using the DuBois and DuBois formula:24.DuBois D. DuBois E. A formula to estimate the approximate surface area if height and weight be known.Arch Intern Med. 1916; 17: 863-871Crossref Scopus (4100) Google Scholar BSA=0.20247×height(m)0.725×weight0.425 The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (KDOQI) definitions of moderate (stage III, GFR, or CrCl 30–59 ml min−1) and severe (stage IV, CrCl, or GFR 15–29 ml min−1) CKD were used.11.National Kidney Foundation K/DOQI Clinical Practice Guidelines for Chronic Kidney Disease: evaluation, classification, and stratification: Part 4. Definition and classification of stages of chronic kidney disease.Am J Kidney Dis. 2002; 39: S46-S75Abstract Full Text Full Text PDF Google Scholar The STATA 8.0 statistical software package (StataCorp, College Station, TX, USA) was used to estimate risk factor levels taking appropriate account of the complex survey design (using the 'svy' command for all analyses) and using weights derived from the 2000 Thai National Census. Estimates of means and proportions (with s.e. or CIs) were calculated for the overall population and for population subgroups defined by a range of different characteristics of interest. Comparison of risk factor levels between population subgroups was performed using t-tests, analysis of variance derived from linear regression models for continuous variables, and χ2 tests for categorical variables. Comparisons of results from previous surveys done in other countries were performed using published proportions, which were calculated taking population weights into account. We derived weighted proportions within Thailand, as described above, and compared them to the published proportions from other countries using χ2 tests to test for differences. Two researchers employed by the funding source were members of the Study Steering Committee that designed the study. However, the funding source had no involvement in the data collection, data analysis, data interpretation, writing of the report, or the decision to submit the paper for publication. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication. The InterASIA study was funded by a contractual agreement between Tulane University (LA) and Pfizer Inc. (NY). Two researchers employed by Pfizer Inc. were members of the Steering Committee that designed the study. However, the study was conducted, analyzed, and interpreted by the investigators independent of the sponsor. This work was also supported by an Australian National Health and Medical Research Council Program Grant. V Perkovic was supported by a Royal Australasian College of Physicians Quintiles Clinical Research Fellowship, B Neal by a fellowship awarded by the National Heart Foundation of Australia, and A Cass by a fellowship awarded by the National Health and Medical Research Council of Australia. We gratefully acknowledge the assistance of Dr Frederick Van Lente in calibrating the creatinine measurements, the provision of unpublished data by the Ausdiab Steering Committee, and the statistical advice from Mr Sam Colman.
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