Lifetime and age-conditional risk estimates of end-stage kidney disease requiring maintenance dialysis in Japan

Easily understandable statistics are essential for communicating the absolute risk of end-stage kidney disease (ESKD) to the lay population, policy makers, and health service providers, and for predicting the disease burden of ESKD. We previously reported the age-standardized incidence [1] and mortality rates [2‐5] of ESKD. An alternative measure is lifetime risk, an epidemiologic measure that expresses the probability of disease in the remaining lifetime for an index age. Lifetime risk is often the preferred measure used in public health communications, as it is perceived to be both informative and easily understandable.

To date, no studies have reported on the lifetime risk of ESKD in the Japanese population. Using data from the Japanese Society of Dialysis Therapy (JSDT), we estimated the lifetime risk of ESKD by sex in Japan.

Table 1 shows a composite life table by sex, which includes the cumulative probability of developing ESKD from birth and cumulative probability of dying without ESKD from birth. In this hypothetical population of 10 million live births, 968,194 men and 2,511,379 women live to be over age 95 years. The numbers of people who develop ESKD in this hypothetical cohort peak in the 75–79 age group in men and in the 80–84 age group in women. With the exception of a relatively large number of infant deaths, the number of deaths due to other causes rises through the 85–89 age group and then falls in men, whereas the number rises with age in women.

The cumulative incidence of ESKD from birth begins to rise at approximately age 40 years and nearly plateaus around age 90 years in both sexes (Fig. 1). The cumulative lifetime incidence of ESKD from birth was 3.14% [95% confidence interval (CI) 3.10–3.18%] for men and 1.42% (95% CI 1.39–1.44%) for women. These probabilities illustrate that approximately 1 in 32 men and 1 in 71 women in Japan will develop ESKD that results in maintenance dialysis therapy during their lifetime.

Tables 2 and 3 show age-conditional probabilities of developing ESKD by sex. ‘Eventually’ denotes the residual lifetime probability of those who have not developed ESKD at ‘Current age.’ For example, a male who has not developed ESKD at age 60 years has a 1.69% (95% CI 1.66–1.72) chance of developing ESKD before age 80 years, and a 2.63% (95% CI 2.60–2.67)—or 1 in 38 (95% CI 37–38)—chance of developing ESKD during his lifetime.

This study estimated the lifetime risk of ESKD in Japan by sex, revealing that the risk is higher in men than in women of equal age; approximately 1 in 32 men and 1 in 71 women in Japan possibly develop ESKD that results in maintenance dialysis therapy in their lifetime. We also determined age-conditional probabilities of developing ESKD by sex. These easily understandable statistics will be useful for assisting in public health education and planning in Japan.

Our study showed considerable sex-dependent differences in the lifetime risk of ESKD in Japan. This is in line with previous studies from other countries [12‐14] that have found that men have higher lifetime risks of ESKD than women. Using cohort data of adults residing in Alberta, Canada, the lifetime risk of ESKD among those without ESKD at age 40 years was estimated to be 2.66% (95% CI 2.57–2.75%) for men and 1.76% (95% CI 1.69–1.83%) for women [12]. Using European Renal Association-European Dialysis and Transplant Association (ERA-EDTA) Registry data, the cumulative lifetime risk of ESKD up to age 90 years in Europe was estimated to be 1.40% or 0.73% for 40-year-old men or women, 1.32% or 0.68% for 50-year-old men or women, and 1.18% or 0.58% for 60-year-old men or women, respectively [13]. Using data from the United States Renal Data System (USRDS), the cumulative lifetime risk of ESKD from birth to age 100 + years in the total US population was estimated to be 3.96% (95% CI 3.93–3.99%) for men and 2.84% (95% CI 2.69–2.74%) for women [14]. Although simple comparisons cannot be made due to differences in methods and age categories used in each study, reported lifetime risk estimates of ESKD are less than 4% worldwide and are higher in men than in women. One possible explanation for the sex-dependent difference would be the higher incidence of ESKD in men than in women. According to the 2018 USRDS annual data report [15], the incidence of treated ESKD cases was substantially higher among males than among females in almost every country. The sex-dependent differences in the incidence of treated ESKD cases are thought to be due to, not only differences in the rate of chronic kidney disease (CKD) progression, but also differences in non-biological factors, such as personal preference and access to care [16].

Notably, our estimated lifetime risk of ESKD in Japan was lower than that reported for the United States [14]; these data were obtained using the same life-table methods of Fay [9] and Fay et al. [10] with DevCan software developed at the National Cancer Institute [11] (notably, the upper age range was 100 + years in the US study [14] whereas it was 95 + years in the present study). One might wonder why lifetime risk of ESKD in Japan was lower than that of the United States, given that the prevalence of treated ESKD is higher in Japan [15, 17]. While prevalence is influenced by both the rate at which new cases are emerging and the average duration of the disease, lifetime risk is influenced by the rate at which new cases are emerging but not the average duration of the disease. Although the prevalence of treated ESKD in Japan is higher than that in the United States, the incidence of treated ESKD in Japan is lower than that in the United States [15]. This explains why the lower estimated lifetime risk of ESKD in Japan than in the United States [14].

Compared to cumulative lifetime risks of other diseases in Japan, the estimated lifetime risk of ESKD was much lower. For example, the lifetime probability of developing cancer in 2001 was estimated to be 49.01% for men and 37.36% for women. These probabilities mean that 1 in 2 men and 1 in 3 women will develop cancer during their lifetime [18]. The cumulative lifetime incidence risk of gastric cancer was estimated to be 11.4% (1 in 9 people) for men and 5.7% (1 in 18 people) for women [19]. As for cardiovascular diseases, lifetime risk estimates of acute myocardial infarction at age 45 years, adjusted for competing risk of death, were 16.24% for men and 11.60% for women, based on data from a cohort of adults residing in Suita city, Japan (the Suita study) [20]. Using the same data, the lifetime risk of stroke at age 45 years, adjusted for competing risk of death, was estimated to be 18.93% for men and 20.18% for women [21].

Of course, a simple comparison between ESKD and other diseases is not feasible, and the meaning of lifetime risk values differs between ESKD and other diseases such as cancer and cardiovascular diseases. Some patients with cancer or cardiovascular disease, for example, may achieve cure, whereas there is no cure for ESKD. In other words, many people with ESKD live long lives while on dialysis or after having a kidney transplant without ever achieving a complete cure.

There are several limitations that need to be considered to adequately interpret our results. First, we defined an incident case of ESKD as a patient with loss of kidney function that resulted in maintenance dialysis therapy. Thus, only patients who had undergone dialysis treatment were included, as data were not available for patients who had not initiated dialysis or had undergone pre-emptive kidney transplantation in Japan. However, the number of patients who had not initiated dialysis were not included in the studies from other countries [12‐14]. Furthermore, the number of pre-emptive kidney transplant patients is small in Japan, with only 101 patients being reported in 2009 [6]. Second, we assumed that both the number of incident cases of ESKD and the number of ESKD deaths for zero-year-olds were zero because these data were not available. However, given that both the number of incident cases of ESKD and the number of ESKD deaths for the 0–4 age group were very small, this assumption is unlikely to have had a major impact on our estimates. Finally, lifetime risk estimates are based on the assumption that exposure to risk- and age-specific rates remains stable. Regarding individual risk prediction, a limitation of lifetime risk estimates is that they do not take into account individual behaviors and risk factors, but are based on population-based data. For individual risk, the estimated lifetime risk will vary according to the individual’s remaining life expectancy, risk factor profile, and risk factor management success over time.

Despite these limitations, to the best of our knowledge, this study is the first to report the lifetime risk and age-conditional probability of ESKD in Japan. As the data were extracted from a nationwide survey of Japanese dialysis facilities and a national census, our findings should be broadly generalizable to the Japanese population. Furthermore, the method used in this study is easy to use for estimating cumulative incidence based on survey data. Enhanced awareness of these issues would enable nephrologists and healthcare professionals to advocate for the need to prevent the development and progression of CKD.

The present study revealed that the cumulative incidences of ESKD from birth until age 95 years in Japan were 3.14% (95% CI 3.10–3.18%) and 1.42% (95% CI 1.39–1.44%) for men and women, respectively. These probabilities illustrate that approximately 1 in 32 men and 1 in 71 women in Japan will develop ESKD that results in maintenance dialysis therapy in their lifetime. This easily understandable information can be used to assist in public health education and planning.