Burden of chronic kidney disease on the African continent: a systematic review and meta-analysis

Chronic kidney disease (CKD) is a leading cause of morbidity and mortality in both developed and developing countries, with an estimated 10% of the population worldwide having CKD in 2015 [1, 2]. Studies have consistently shown that African descendants are at increased risk for CKD occurrence and progression to end-stage renal disease (ESRD) [3, 4]. Many African countries are currently undergoing rapid epidemiological transitions and are confronted with the double burden of communicable and non-communicable diseases, in part driven by the adoption of western lifestyles, changes in the built environment, and the rapid urbanization [5]. This dual burden has led to a consequential rise in the number of people affected by CKD on the African continent [6].

Given the constant rise in its risk factors in Africa [7, 8], CKD is increasingly recognized as a major public health threat, against a background of limited access to renal replacement therapy (RRT) [6]. Hence, in Africa, prevention and early detection of CKD in order to slow its progression are of paramount importance. For this purpose, a better understanding of the current prevalence of CKD in Africa is urgently needed. Although the number of reports on CKD prevalence across Africa has increased in recent years, accurate data on its exact magnitude on the continent are still lacking [6]. The only systematic review of CKD prevalence in Africa was limited to sub-Saharan countries, included studies published between 1962 and 2011, and highlighted the inability to make definitive inferences due to the poor quality of included studies [9]. We conducted a systematic review and meta-analysis of the contemporary evidence on CKD prevalence in adults living on the African continent, in order to establish baseline figures against which future trends can be monitored.

We used a prospective protocol (PROSPERO CRD42017054445) [10] to perform this review according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines [11].

Our review including 98,432 individuals found a prevalence of 15.8% for CKD stages 1–5 in the general population of adults living on the African continent. Additionally, we showed that 4.6% of adults living in Africa have moderate or severe decreases in kidney function (i.e. CKD stages 3 to 5). The prevalence of CKD was higher in sub-Saharan Africa than North Africa, and nearly two times higher in high-risk populations than in general populations. The three main equations used to estimate the kidney also yielded different results. The Cockcroft formula showed a prevalence that was higher than prevalence obtained using MDRD or CKD-EPI equations. We found substantial heterogeneity across the studies and in subgroup analyses, and no evidence of publication bias across studies reporting on CKD prevalence in general populations of Africa.

Our review is the first to comprehensively assess the prevalence of CKD in adults living on the African continent. A previous systematic review on CKD prevalence limited to sub-Saharan Africa included articles published between 1962 and 2011; amongst which 32 (35.6%) were published before 2000 [9]. The vast majority (65.3%) of studies included in our review were published between 2012 and 2016, a more contemporary period. Our findings supplement previous studies and reviews on CKD by providing an updated and comprehensive synthesis of data on the magnitude of CKD in the African continent.

The CKD prevalence in this review is slightly higher than that reported in African countries in a recently published systematic review on the global CKD prevalence [21]. However, their review included data from three African countries (5497 individuals) and is therefore much less representative of the entire continent. The overall estimated prevalence of CKD stages 1–5 in the general population found in our review is similar to that (13.1%) found in the United States [22]. However, the prevalence of CKD in our review was higher than that found in general populations of adults living in four Asian countries (West Malaysia, Korea, China, and Taiwan) and Europe [23‐27]. The prevalence of CKD stages 3–5 in our study was lower than that found in the United States (8.0%), and higher than that found in two Asian countries [23‐27]. The prevalence of CKD in high-risk populations found in our review is similar to that found in a high-risk population (with diabetes or hypertension) in Korea (39.6%) [28]. Likewise, our estimate in high-risk subjects is comparable to the prevalence of CKD in a sample of hypertensive subjects in the Unites States [29].

While the attention of policy makers is finally extending beyond communicable diseases to the non-communicable diseases, particularly the cardiovascular disease (CVD) epidemic, it is not fully appreciated that this is accompanied by an epidemic of CKD. Our estimates indicate that CKD may be more common than diabetes which has an estimated prevalence of 3.2% in people aged 20 to 79 in sub-Saharan Africa [30]. The rapid rise in the number of people with hypertension or diabetes [7, 8], combined with the HIV pandemics, and the increased survival in individuals taking antiretroviral therapy are predicted to drive the burden of CKD in Africa [31]. Like hypertension or diabetes, CKD has consistently been shown to be associated with higher risk of mortality from CVD [26, 32, 33]. This situation is further compounded by the fact that a vast majority of people with CKD are unaware of their condition until they progress to later stages [34, 35]. Various observational cohort studies have shown that the increased risk in CVD mortality in CKD patients is apparent in the early stages of the disease, and nearly 40% of deaths from CKD occur prematurely (before age 65) [26, 32]. This highlights the need for interventions earlier in the process. Effective strategies can slow the progression of CKD and may help reduce the risk of CVD [14].

Our review points out the critical need of data in many parts of Africa that would help to further characterize the magnitude of CKD burden on the mother continent. Indeed, out of the 54 African countries, 32 were not included in this review. Although, the number of population-based studies on CKD prevalence has somewhat increased in the recent years, many African countries are still lagging behind. African countries must be encouraged to conduct population-based surveys of CKD prevalence such as the MAREMAR (Maladies Rénales Chroniques au Maroc) [36] project on a regular basis, in order to monitor time trends of CKD prevalence with comparable methodologies. African countries are also encouraged to incorporate CKD surveillance in existing data collection opportunities such as the WHO STEPwise approach to Surveillance surveys. Moreover, there is an urgent need for African nations to establish and sustain renal registries at both national and regional levels [37]. On a continent where access to healthcare is restricted due to economic constraints, the publication of registry data would be a cost-effective approach to draw the public and policy makers’ attention to the underappreciated problem of CKD, and help efforts to prevent, detect, and treat CKD at much earlier stages [37‐39]. An African renal registry would facilitate the sharing of expertise across all the nations using this common platform, and lead to more effective patient advocacy, public health policy and fundraising [37].

Our review has some limitations. First, we found substantial heterogeneity in prevalence estimates, which was not completely explained by subgroup analyses. This may in part be explained by between-study differences in methodology and population structures, but they may also represent true regional differences in disease burden. Second, our ability to assess the quality of included studies was limited by the incomplete methodological information provided in some studies. Third, primary studies lacked data on important covariates that could have been used in meta-regression analyses to further explore and adjust for the sources of variations in prevalence between studies. Additionally, the majority of surveys did not follow patients for 3 months to confirm the diagnosis of CKD. Previous evidence suggested that a single measurement of eGFR may overestimate CKD prevalence [40]. These limitations notwithstanding, our study has several strengths. First, we used a comprehensive review protocol [10], and made extensive efforts to identify all the available evidence by searching multiple electronic databases without language restrictions; we applied an Africa-specific search filter [12], and adhered to pre-specified study selection criteria [10]. Second, we critically appraised the methodological quality of studies with a standard quality assessment tool for prevalence studies [15]. Finally, we used the Freeman-Tukey single arcsine transformation to stabilize the variance of prevalence estimates before pooling, therefore limiting the effects of studies with small and large prevalence estimates on the pooled estimates [16].

Key unaddressed issues in the detection of CKD in Africa include the absence of reliable and valid methods for assessing kidney function [41]. Our findings showed that CKD prevalence estimates can vary substantially depending on the equation used. Although the MDRD and CKD-EPI have been shown to be superior to the Cockcroft-Gault formula, the validity of those methods in African populations remains to be established [41, 42]. Furthermore, although it is widely accepted that CKD is associated with an increased all-cause and CVD mortality risks, the extent to which this applies to populations living on the African continent remains unclear. Most observational studies of adverse health outcomes in CKD patients were conducted in developed countries, which may not necessarily generalize to African populations [43]. African countries are encouraged to establish prospective multicenter cohorts of CKD patients such as the CRIC (Chronic Renal Insufficiency Cohort) Study [44], in order to examine risk factors for CKD progression and CVD tailored to their region, identify high-risk subgroups, and assess the role of genetic factors such as Apolipoprotein L1 (ApoL1) [45] variants in the genesis and progression of CKD in people living on the African continent.

In summary, the substantial burden of CKD on the African continent found in this review highlights the need for a concerted action to prevent the high health and economic burden that this condition entails.