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Table 1 Comparisons of Key Characteristics Among Areas with Reported CKDu

From: Global dimensions of chronic kidney disease of unknown etiology (CKDu): a modern era environmental and/or occupational nephropathy?

Risk Factor/Characteristic Sri Lanka Central America India Egypt
Reported Areas North Central Province [3] Most reports from El Salvador and Nicaragua but appears to extend across Pacific coast areas of Central America [37] In state of Andhra Pradesh: coastal in Uddanam area and 30–40 km inland in Chimakurthy mandal [52] Reported in El-Minia Governorate [53]
Present, although to a lesser extent, in Uva and North Western Provinces [36] In India overall, highest in south which included Andhra Pradesh [44]  
Age Wide age range; increased prevalence of eGFR ≤ 60 ml/min per 1.73 m2 in fourth and fifth decades [12] Third to fifth decade [37] In India overall, younger than patients with diabetic nephropathy [44] Mean age of 46 (n = 800 patients on renal replacement therapy) [53]
Sex Female > male overall but male > female for CKD stage III –IV [3] Male > female [37] Male > female in Uddanam area, [6] and in India overall [44] Male > female [53]
Geographical Characteristics Rural [12] Rural, especially the lowlands along the Pacific coast [37] Rural - coastal and inland [52] Rural [53]
Dry weather except for two monsoon periods [36] Coastal communities at lower elevations (<500 m) [45]   
Occupations Chena (vegetable and other crops) farmers; rice farming had a lower risk compared to chena farming [3] Risk in coastal agricultural workers but not in agricultural workers employed at elevations > 500 m; sugarcane workers studied in both locations [45] In Uddanam area, agricultural cultivation of coconuts, rice, jackfruit and cashews [6] Farming [54]
Compared to coastal agricultural workers, risk lower in service sector and agricultural workers at higher elevations [55]
Intense heat noted in working conditions in Central America [49]   
Socio-economic Status Low Low In India overall, lower than those with diabetic nephropathy [44] Not reported
Pathology In biopsies from 211 CKDu patients, the main pathological features were interstitial fibrosis, interstitial inflammation and tubular atrophy of varying degrees [10]. Authors concluded that interstitial fibrosis was the earliest detectable pathological change. A study of 57 CKDu patients observed chronic tubulointerstitial nephropathy [56]. The authors considered the glomerular and vascular damage also observed to be secondary to the tubulointerstitial damage. Chronic tubulointerstitial nephritis (no details as reported in abstract from conference proceedings) [6] Not reported, biopsies rarely performed [53]
Interstitial fibrosis and tubular atrophy, sometimes with nonspecific interstitial mononuclear cell infiltration, predominated; glomerular sclerosis, glomerular collapse, and features of vascular pathology such as fibrous intimal thickening and arteriolar hyalinosis also common (n = 57) [11] A study of 8 CKDu patients reported extensive glomerulosclerosis (29 %-78 %) and signs of chronic glomerular ischemia in combination with tubular atrophy and interstitial fibrosis but only mild vascular lesions [9]. The authors concluded that both glomerular and tubulointerstitial compartments were damaged by CKDu.
  Biopsies in 26 patients (19 in CKD stages 1–3) reported as consistent with tubulointerstitial disease; immunofluorescence tests for immune-mediated kidney injury were negative [12]    
Presentation Slow progression; minimal proteinuria (mean 24 h urine protein = 612.8 mg in 109 participants) without active sediment; bilateral small echogenic kidneys [12] Minor or no proteinuria or albuminuria [6, 55] In India overall, advanced CKD, few initial symptoms, absent or mild hypertension and little or no proteinuria [44] Not reported
Urinary excretion of alpha-1-microglobulin elevated in CKDu patients, even in the earliest CKD stage, compared with first-generation related controls residing in the same community and Japanese controls, suggesting early renal tubular damage in CKDu [57] Small echogenic kidneys on ultrasound [37] In Uddanam area, proteinuria prevalence of 20 % in males and 12 % in females [6]
Urinary symptoms, when present, are positive for pyuria and leukocyte esterase but urine culture negative [37]   
Magnitude Age-standardized prevalence (95 % CI) of albumin–creatinine ratio ≥30 mg/g on two separate tests [3]: Mortality from chronic renal failure (2007) [58] CKDu is second most common cause of CKD in India (16.0 %) after diabetic nephropathy (31.3 %) [44] Unknown etiology, at 27 %, was leading cause of end-stage renal disease (ESRD) followed by hypertension at 20 % and glomerulonephritis at 11 % [53]
  El Salvador
15.1 % in Anuradhapura Men: 85.5/100,000
20.6 % in Polonnaruwa Women: 34.1/100,000
22.9 % in Badulla Men: 66.2/100,000
16.9 % (15.5 %–18.3 %) in women Women: 22.3/100,000
12.9 % (11.5 %–14.4 %) in men Men: 9.5/100,000
Stage 3 and 4, respectively: Women: 7.0/100/000
23.2 % and 22 % in men Men: 3.0/100,000
7.4 % and 7.3 % in women Women: 2.5/100,000