#1867 Spanish renal health cohort: Mulagua study

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Abstract Background Chronic kidney disease (CKD) is a serious Health problem. It is the eighth leading cause of death worldwide, is going to be the fifth in 2040, and the second in 2100. CKD is a first-order disease, carrying a high burden to the health system: approximately 5% of the health budget is used to cover renal replacement therapy. In Spain, the "estimated prevalence" of CKD is 10% and I supposed to increase to 18% in 2040 and 24% in 2100. However, the "real prevalence" of CKD in Spain is unknown since the few population studies available have discrepant data, making impossible to devise strategies for early prevention. This is probably due to the silent nature of CKD, which symptoms go unnoticed for years, until progress to more advanced stages. Also, the unreliability of classic markers of kidney dysfunction, such as serum creatinine and the estimation by formulas, which present a mean error of ±30% with respect to the measured renal function, adds another factor of uncertainty. The population studies available rely on the estimation of renal function which makes them not fully reliable. We aimed to develop a population-based study in the region of Mulagua, in the towns of Agulo and Hermigua, Canary Islands, Spain. We will analyze a large group of adults subjects who will undergo the plasma clearance of iohexol with dried blood spots (iohexol-DBS) to measure GFR. Specific aims: To evaluate (1) the real prevalence of CKD and its stages using measured GFR; (2) the prevalence of occult renal disease (ORD) i.e. GFR <60 ml/min + serum creatinine in the normal range and estimated GFR >60 ml/min with or without albuminuria; (3) the error of formulas in estimating CKD and its stages; (4) the association of classic risk factors with CKD (hypertension, overweight-obesity, diabetes, dyslipidemia); (5) the prevalence of CKD by age ranges; (6) gender differences in the prevalence of CKD; (7) establish a baseline group for prospective studies. Method Cross-sectional study. Inclusion criteria: 1. Age over 18 years; 2. Ambulatory status; 3. Clinical stability. Exclusion criteria: 1. allergy to iodinated contrasts; 2. Inability to understand the protocol; 3. Pregnancy; 4. Active cancer. Measured GFR: All patients will undergo plasma clearance of iohexol by dried blood spot analysis (iohexol-DBS). Estimated GFR by formulas in the baseline serum sample, creatinine and cystatin-C based formulas. Clinical variables: biochemistry analysis, albumin/creatinine ratio, demographic data (date of birth, sex, race), anthropometric data (weight, height, abdominal circumference, BMI, blood pressure), tobacco and alcohol consumption, underlying disease (if any), treatments received (if any) Surveys: dietary adherence, exercise and sedentary lifestyle and socio-economic. Serum/plasma/urine/DNA banks: the study presented in this project is cross-sectional and will be the basis for different prospective studies creating nested cohorts in which the association between variables in different subgroups will be studied. Sample size and calculation The main objective of our study at this early stage is to assess the prevalence of CKD in a representative population of the Spanish population using a precise and accurate method (iohexol-DBS). To do this, we have calculated the sample size as follows: Spanish population (47,435,537), with a confidence level (1-alpha) of 95%, a precision of 1.6%, an expected proportion of CKD (10%), the sample size should be 1352, but considering losses of 15%, the total sample to observe 10% of CKD with this level of precision would be 1576. If losses of 10% are considered, the total sample would be 1501. In principle, this is our study population (n = 1576). Ad-interim studies will be carried out to analyse partial prevalence of CKD and to see the need to increase the sample size. The population of the two towns is sufficient to cover these figures. The sample size is in line with the Renal Iohexol Clearance Survey in Tromsø 6 (RENIS-T6) study where the authors studied kidney function in 1621 inhabitants, a representative sample of middle-aged people from the general Norwegian population.

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