The Rising Burden of Hypertensive Renal Disease in Low‐Income Countries: Is it Time to Take Action?

Recent surveys indicate that low‐income populations are facing a rising epidemic of noncommunicable diseases that might have impact on their social and health outcomes. These diseases are therefore showing increasing recognition in resource‐poor countries and a declaration of the United Nations. General Assembly has warned against the forthcoming global threat caused by these conditions.1 Chronic kidney disease (CKD) is a noncommunicable condition and epidemiological data obtained in the Global Burden of Disease Study indicate that during the past two decades, the worldwide mortality rate associated with renal disease has doubled.2 Unfortunately, because of the absence of renal registries, there are no reliable estimates of the prevalence of CKD in the majority of economically developing countries. Nonetheless, it has been estimated that in the next decade, more than two thirds of patients with end‐stage renal failure will be living in countries where the internal product per capita is less than US $1500 per year and half the population lives on less than US $1 per day.3

Sub‐Saharan Africa is a heterogeneous region composed of 47 countries that occupy most of the land mass of Africa, with a population of approximately 800 million people. In this region of the world, noncommunicable diseases are coming under the spotlight, with approximately 2.5 million deaths reported in 2005.3 A recent systematic review and meta‐analysis has shown that CKD is a highly prevalent and potentially increasing condition in sub‐Saharan countries.4 This observation generates major concern when we consider that less than 5% of people who have access to renal replacement therapy worldwide are from sub‐Saharan countries.5 In addition to noncommunicable conditions, many communicable diseases can account for the high incidence of chronic renal disease in this region of the world, including infectious glomerulonephritis, schistosomiasis, leishmaniasis, and, last but not least, human immunodeficiency virus (HIV) infection. However, hypertensive nephropathy is currently retained as the most frequent cause of end‐stage renal disease in this area of the world.6 Studies conducted in Nigeria showed that CKD accounts for more than 10% of hospital admissions7 and that hypertensive nephropathy accounts for 61% of these admissions.8 Similar data were reported in studies of patients from South Africa.9

Today, we are aware that high blood pressure (BP) is a major contributor to the global burden of disease worldwide,10 and hypertension is the main risk factor for mortality and the third cause of global disability‐adjusted life‐years.11 Projections for the next decade indicate that the current estimate of hypertension prevalence worldwide will further increase and, most important, the number of patients with high BP in sub‐Saharan countries will almost double.12 Therefore, it is possible that hypertension will soon become a greater population burden in low‐income than high‐income countries of the world. In fact, although hypertension is more prevalent in industrialized countries, because of the much larger population of developing countries, the rough number of affected patients in these countries will rapidly overtake that of patients in the western world. The burden of hypertension in sub‐Saharan Africa has been the subject of a recent systematic review and meta‐analysis including 33 surveys and involving more than 110,000 individuals.13 Results indicated a pooled prevalence of hypertension of 30% with only 27% of people with hypertension aware of their hypertensive status before the survey. Among these patients, 18% were receiving regular treatment and only 7% had normalized BP values. The findings of this important study revealed a much lower prevalence of hypertension awareness, treatment, and control in sub‐Saharan countries than in other regions of the world, including not only those economically developed but also other low‐income countries.14

On this background, Kaze and colleagues15 sought to investigate the prevalence of CKD, as defined by detection of decreased glomerular filtration rate (GFR) and/or albuminuria, and the relative risk factors in a population of 336 hypertensive Cameroonians who were recruited at the hypertension clinic of the Yaoundè Central and University Teaching Hospital. Patients were well characterized in terms of demographic, anthropometric, and clinical variables and had high rates of comorbidities including obesity, diabetes, dyslipidemia, and gout. More than one third of them used self‐medication with unconventional preparations. The majority of these patients (78.9%) had uncontrolled BP despite the fact that frequency of use of conventional antihypertensive drugs in these patients was not significantly different from patients who had BP at target. Approximately one third of hypertensive patients had GFR <60 mL/min/1.73 m² and slightly more than one third had detectable urinary albumin losses, with nearly half of patients with evidence of CKD. No significant differences in GFR and prevalence of albuminuria were observed between hypertensive patients who had controlled or uncontrolled BP, although higher systolic values were associated with both reduced GFR and detection of albuminuria. Additional predictors of CKD were identified in a logistic regression analysis with evidence that age is the major independent factor predicting GFR reduction, whereas female sex seemed to be protective against albuminuria.

It is well‐known that the method used for identification of renal disease might affect prevalence estimates. An important issue in the detection of CKD in the majority of studies conducted in sub‐Saharan countries is the lack of validated and reliable measurements. Assessment of urinary protein excretion was used most frequently and previous studies conducted in this geographic area reported prevalence rates ranging from 6% to 24%.4 Other studies conducted in sub‐Saharan countries have assessed GFR either by use of the Cockcroft‐Gault, Modification of Diet in Renal Disease, or Chronic Kidney Disease Epidemiology Collaboration formulas, with estimates obtained with the Cockcroft‐Gault formula tending to be higher in all studies, although differences from other methods of calculation were not significantly different.4 To overcome this problem, Kaze and colleagues have reported measurements of GFR according to all three common estimators. No significant differences in the renal outcomes were observed across these estimators, suggesting that all might be potentially applicable in African populations.

With the obvious limitation of a sample size that is distant from the dimension of a true epidemiologic study, results of the study by Kaze and colleagues do provide important information on hypertension and CKD in sub‐Saharan Africa. The percentage of hypertensive patients with adequate control of BP in this geographical area is much lower and the prevalence of kidney disease is much higher than in the rest of the world. Previous studies conducted in neighboring countries have reported similar estimates of the prevalence of CKD.16, 17 Although additional conditions that can frequently cause renal disease in sub‐Saharan countries such as HIV, hepatitis B virus, hepatitis C virus, and other infections were not systematically screened in the patients studied by Kaze and colleagues, it seems reasonable to attribute most of the burden of renal abnormalities detected in the hypertensive Cameroonians to hypertension‐related renal disease. Hypertensive nephroscerosis is in fact one of the most frequent causes of end‐stage renal disease worldwide,18 and strong evidence obtained in the United States in persons of African descent indicates that in these patients, high BP is more frequently associated with renal disease and a more rapid fall of renal function than in Caucasians.19 Excess renal damage in hypertensive African Americans has been explained by a genetic predisposition associated with environmental amplification caused by social factors that facilitate profibrotic mechanisms in the kidney and progression to a more aggressive form of glomerulosclerosis.20 These mechanisms might well have a role in the hypertensive populations of sub‐Saharan countries, although the worrisome scenario depicted by Kaze and colleagues could be more likely explained by lack of organized screening programs and difficulties in access to affordable healthcare. These shortcomings could cause late referral of hypertensive patients with CKD to the appropriate site of care and delay preventive interventions.21

In a continent where chronic noncommunicable diseases are progressively coming to the forefront, CKD should not be overlooked. Important social and demographic changes are occurring in Africa, with more and more rural populations moving to urban areas and adopting westernized lifestyles, with subsequent exposure to risk factors for chronic disease. Identification and control of hypertension has been endorsed by many public organizations22 and relatively inexpensive medications could be made readily available in developing countries. However, many obstacles, including lack of dedicated infrastructures, inadequate awareness about hypertension of patients and health operators, and poor adherence to treatment, make it difficult to obtain appropriate control of hypertension and its renal complications in sub‐Saharan countries. Adequate programs are urgently needed in these countries to cope with the rising burden of hypertensive renal disease.

Disclosure

The authors report no relevant conflicts of interest.