**Acknowledgements**

This study was carried out with financial support from "Fondos Mixtos-CONACyT- Sonora State Government (No. SON-2004-C01-004). The authors sincerely thank "Secretaria de Sal‐ ud (SS)" for letting conduct part of the analysis in laboratories of General Hospitals in Obre‐ gon city and Navojoa as well "Centro Avanzado de Atención Primaria a la Salud (CAAPS)" in Hermosillo, Sonora. The authors express recognition to the contribution of graduate stu‐ dents from University of Sonora (2010-2004): Enoc Hernández Montiel, Yessica Fabiola Gó‐ mez Hernández, Lidia Sarai Güitrón Ochoa, Ana Arely Villegas Castro, Mizar Ethzalé Martínez Romero, Graciela Lizeth Pérez González, Luis Jesús Villarreal Gómez and M. Sc. Edna Delia Molina Romo.
