Background: We previously estimated the prevalence of chronic kidney disease (CKD) stages 3-5 at 19.1 million based on data from the Japanese annual health check program for 2000-2004 using the Modification of Diet in Renal Disease (MDRD) equation multiplied by the coefficient 0.881 for the Japanese population. However, this equation underestimates the GFR, particularly for glomerular filtration rates (GFRs) of over 60 ml/min/1.73 m(2). We did not classify the participants as CKD stages 1 and 2 because we did not obtain proteinuria data for all of the participants. We re-estimated the prevalence of CKD by measuring proteinuria using a dipstick test and by calculating the GFR using a new equation that estimates GFR based on data from the Japanese annual health check program in 2005.
Methods: Data were obtained for 574,024 (male 240,594, female 333,430) participants over 20 years old taken from the general adult population, who were from 11 different prefectures in Japan (Hokkaido, Yamagata, Fukushima, Tochigi, Ibaraki, Tokyo, Kanazawa, Osaka, Fukuoka, Miyazaki and Okinawa) and took part in the annual health check program in 2005. The glomerular filtration rate (GFR) of each participant was computed from the serum creatinine value using a new equation: GFR (ml/min/1.73 m(2)) = 194 x Age(-0.287) x S-Cr(-1.094) (if female x 0.739). The CKD population nationwide was calculated using census data from 2005. We also recalculated the prevalence of CKD in Japan assuming that the age composition of the population was same as that in the USA.
Results: The prevalence of CKD stages 1, 2, 3, and 4 + 5 were 0.6, 1.7, 10.4 and 0.2% in the study population, which resulted in predictions of 0.6, 1.7, 10.7 and 0.2 million patients, respectively, nationwide. The prevalence of low GFR was significantly higher in the hypertensive and proteinuric populations than it was in the populations without proteinuria or hypertension. The prevalence rate of CKD in Japan was similar to that in the USA when the Japanese general population was age adjusted to the US 2005 population estimate.
Conclusion: About 13% of the Japanese adult population-approximately 13.3 million people-were predicted to have CKD in 2005.