[1] Inst Guatemalteco Seguridad Social, Guatemala City, Guatemala
[2] Ctr Hemodialisis, San Salvador, El Salvador
[3] Fondo Social Emergencia Salud, Tierra Blanca, El Salvador
[4] Hosp Dr RA Calderon Guardia, Serv Nephrol, Caja Costarricense Seguro Social, San Jose, Costa Rica
[5] Inst Nacl Cardiol Ignacio Chavez, Div Nephrol, Juan Badiano 1,Col Secc 16, Mexico City 14080, DF, Mexico