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Chronic interstitial nephritis in agricultural communities (CINAC) is a form of kidney disease that is increasingly prevalent in some tropical and subtropical regions worldwide and characterized by progressive impairment of kidney function in the absence of hypertension, diabetes and glomerulopathy. We aimed to determine the prevalence of CINAC and diagnostic performance of the salivary urea nitrogen (SUN) dipstick test in the northern region of Senegal.
We conducted a prospective study from February 1st to August 31st, 2023. After receiving informed consent, we included 300 male volunteer agricultural workers, aged > 18 years, without any known metabolic, infectious, cardio-vascular or renal disease. Clinical data, results of SUN, blood urea nitrogen (BUN), serum creatinine (SCr), proteinuria and urine sediment were collected for each participant and analyzed. Subjects with renal failure (high SCr, high SUN or active urine sediment) were reassessed three months later to confirm the chronicity of renal failure. CINAC was diagnosed per the Sri Lanka Society of Nephrology criteria. Kidney biopsy was done in uncertain cases. The Youden index was used to determine the optimal SUN threshold for diagnosing renal failure.
The mean age of participants was 39.9±8.1 years (range 23-72 years) and median time as agricultural worker was 11.55 years (range 0.5-35 years).
The rate of impaired kidney function at the first screening was 28.66 % (n=86). Three months later, we diagnosed CINAC in 76 of these 86 subjects (88.37%), resulting in a CINAC rate of 25.33%. Sun exposure was longer in workers with an eGFR<60 ml/min (n=46) compared to subjects with eGFR>60 ml/min (8.02±0.57 hours/day versus 7.71±1.03 hours; p=0.048). A daily water intake of less than 1.5 liter was reported by 73.91% (n=34) of subjects with eGFR<60 ml/min versus 51.57% (n=131) for eGFR>60 ml/min (p = 0.005).
Compared to SCr, SUN test showed a good performance in the diagnosis of renal failure (AUC=0.72 [95%CI 0.66-0.78], p <0.001). SUN test strip pad #2 (i.e., SUN >14 mg/dl) was most informative for the diagnosis of kidney failure (sensitivity 0.79 [95%CI 0.69-0.88]; specificity 0.64 [95%CI 0.47-0.71]).
The high proportion of CINAC in our study warrants further explorations of a potential link between agricultural activities, water intake, sun exposure, and kidney disease in Senegalese adults. The SUN test can provide a rapid and reliable screening tool with good performance compared to SCr.