Contribution: This paper examines the literature dealing with the non-invasive estimate of anemia (NEA), and analyzes if the research is developing scientifically with adequate empirical validation. This paper reveals a trend in NEA studies towards an increasing interest in estimating anemia using conjunctiva pallor. Background: Supporting clinical developments and processes to reduce personal discomfort and allow extensive screening needs substantial efforts in researching non-invasive techniques to evaluate anemia. Research Questions: The main aims of this study are the analysis of the area of interest explored in the NEA literature, the evaluation of the peculiarities of papers, giving special consideration to empirical ones, examining them from the point of view of the daily improvement of doctors and healthcare personnel activities and the daily life of patients; and the identification of any considerable research gap to encourage further investigations on new topics. Methodology: The systematic mapping study has been elected as the optimal approach to probe the NEA literature since it defines a rigorous process for data retrieving and interpretation. Findings: Research in this sector is very active, especially in the most populated countries in the world and focuses on improving the technologies currently on the market and on proposing new solutions, especially portable and usable by everyone. A new trend in camera and smartphone-based devices is identified.