Background: Complete blood count is one of the most ordered tests in clinical and surgical practice. However, it is important to know how to properly interpret it. The aim of this study was to measure the level of knowledge that health professionals have concerning the proper interpretation of the CBC test. Methods and Findings: The article reports and analyzes the responses of questionnaires on the interpretation of CBC results applied in a sample of one hundred health professionals. A semi-structured tool was developed and composed of topics regarding sociodemographic data, a specific knowledge test on CBC, and a self-evaluation on the interpretation and the importance of the test. All participants scored less than 90% on the questionnaire, a result that was established as unsatisfactory regarding CBC interpretation. Only physicians and biomedical scientists showed suitable knowledge on the interpretation of hematological terms. Conclusion: Despite the fact CBC is one of the main tests in clinical routine, our results showed deficits in knowledge on the theme by health professionals. Perhaps these results may help to reinforce the importance of multidisciplinarity and also highlight the deficiencies of training in the different professions studied.