BACKGROUND To question the usefulness of the lab analysis considered routine testing for the identification of abnormalities in the surgical care. OBJECTIVE To determine the percentage of unnecessary laboratory tests in the preoperative assessment as well as to estimate the unnecessary expenses. METHODS A descriptive, cross-sectional study of patients referred for surgical evaluation between January 1st and March 31st 2013. The database of laboratory testing and electronic files were reviewed. Reference criteria from surgical services were compared with the tests requested by the family doctor. RESULTS In 65% of the patients (n=175) unnecessary examinations were requested, 25% (n=68) were not requested the tests that they required, and only 10% of the patients were requested laboratory tests in accordance with the reference criteria (n=27). The estimated cost in unnecessary examinations was $1,129,552 in a year. CONCLUSIONS The results were similar to others related to this theme, however, they had not been revised from the perspective of the first level of attention regarding the importance of adherence to the reference criteria which could prevent major expenditures. CONCLUSIONS It is a priority for leaders and operational consultants in medical units to establish strategies and lines of action that ensure compliance with institutional policies so as to contain spending on comprehensive services, and which in turn can improve the medical care.