THE MEANING OF PROTEINURIA IN DEVELOPING COUNTRIES: DATA FROM URBAN AND RURAL SETTINGS IN THE HYDY STUDY

Proteinuria is a recognized early marker of kidney damage and a risk factor to develop chronic kidney disease, and end-stage renal disease (ESRD) as well as being a marker of cardiovascular diseases. In low income countries infectious diseases, mainly post-infectious glomerulonephritis, by increasing proteinuria, add substantial burden in enhancing the global prevalence of chronic kidney disease and are the main cause of ESRD. Few information is available on the different meanings of proteinuria in urban and rural settings. HYDY (HYpertension and Diabetes in Yemen) study is a population-based, cross-sectional survey on 10 242 subjects (5063 male and 5179 female) aged 15-69 years, stratified by age decades, gender and urban/rural residency designed to investigate the prevalence of cardiovascular risk factors such as diabetes, hypertension, and proteinuria and their relationships. Design and methods: The burden of hypertension and diabetes in the population was assessed by taking blood pressure (BP) and fasting glucose (FG) measurements on two visits. BP measurements were obtained with a semiautomatic sphygmomanometer (Omron Ltd, Matsusaka, Japan). Hypertension was defined as systolic BP >= 140 mmHg and/or diastolic BP >= 90 mmHg and/or self-reported use of antihypertensive drugs. Finger-prick blood samples from fasting (> 8 h) subjects were used to measure FG (Accutrend, Roche, Germany). Diabetes was defined as fasting glucose >= 126 mg/dL or self-reported use of hypoglycaemic medications. A urine sample was collected and a dipstick test (Auction sticks A, Menarini, Florence, Italy) was performed, results being decided by visual comparison of the test strip with a color chart. Results of dipstick urinary protein analysis were recorded as follows: negative (0), trace (+/-) or proteinuria (1+, 2+, 3+ or 4+). Odds ratios (OR) with 95% confidence interval (CI) for associations were determined by multivariable logistic regression. Results The survey was completed within 16 months, with an overall response rate of 92% in urban and 94% in rural locations. While hypertension was more prevalent among rural dwellers (adjusted OR 1.23; 95% Cl 1.08 to 1.41), hypertension awareness (0.56; 0.45 to 0.71) and allocation to antihypertensive treatment (0.61; 0.48 to 0.76) were more prevalent among urban residents. Diabetes was less prevalent in rural areas (0.70; 0.58 to 0.85). The presence of urinary protein (trace or more) at dipstick test are presented in table I. Overall, 6.2% of Yemen population aged 15-69 years had proteinuria (>1+) at dipstick test, being more prevalent in rural (7.3%) than in urban residents (5.1%) (OR 1.63; 1.38-1.93). The association of proteinuria with rural setting was evaluated after adjustment for diet habits, self-reported sedentary lifestyle, daily smoking, obesity, abdominal obesity, high cholesterol, hypertension and diabetes. Proteinuria was the only investigated risk condition more prevalent in rural than in urban areas (Figure 1). After adjustment with different models, proteinuria was independently associated with diabetes only among urban residents (1.82; 1.15 to 2.89), whereas the association with hypertension was present both in urban (1.97;1.35 to 2.87) and rural settings (1.93;1.44 to 2.59). Most importantly 3.7% and 5.6% of subjects investigated in urban and rural areas respectively had proteinuria in the absence of hypertension and diabetes. The amount of overlap between hypertension, diabetes and proteinuria among urban and rural dwellers is shown in Figure 2. Differently from hypertension and diabetes, proteinuria showed an inverse relationship with age, thus suggesting a different background Discussion In Yemen the prevalence of proteinuria is higher among rural than urban dwellers. The amount of overlap between hypertension, diabetes and proteinuria indicates that the majority of proteinuria is neither related to hypertension nor diabetes. It is conceivable that hypertension among rural residents might be linked with pre-existing kidney disease. The inverse relationship between proteinuria and age compared with other complications/risk factors also suggests a completely different background. Difference between rural and urban areas might also be caused by the disparity in health care between different Yemenareas.