Prevalence by health areas of chronic kidney disease in the diabetic population of Extremadura in 2012, 2013 and 2014. An observational study Leandro Fernández-Fernández; Javier Goujat-Salas; Carmen Ceballos-Malagón; Manuel Tejero-Mas; Francisco Luis Pérez-Caballero; Francisco Buitrago-Ramírez;