# A Systematic Mapping Study on Research in Anemia Assessment with Non-Invasive Devices
## 1 Introduction  
In reports published by the World Health Organization, it is claimed that anemia is a global health problem, considering that around 25% of the population is affected, with varying degrees of severity [1; 2; 3; 4; 5; 6]. The main factors that cause anemia are iron deficiency, infectious diseases, or genetic factors. Red blood cells and hemoglobin (Hb) concentration levels decrease with anemia and this leads to a reduction in the function of the blood to transport oxygen to the peripheral tissues. The excessive reduction of the availability of oxygen supplied to the cells causes damage to vital organs and then severe anemia has to be monitored steadily. In severe cases, blood transfusion is necessary basing on the Hb measured also daily, normally in the laboratory using a blood sample. This pathology is subtle because it evolves slowly and does not present easily recognizable symptoms. Unequivocal several symptoms appear when the compensatory processes activated by the human body are no more sufficient to guarantee the right quantitative of circulating oxygen. The symptomatology varies according to the severity and type of anemia, but typical symptoms common to all types of anemia include pallor, asthenia, tachycardia, fainting, loss of appetite, nausea, exertional dyspnea [7; 8; 9; 10; 11].  
Anemia can be detected with invasive and non-invasive techniques. Invasive techniques require blood samples; therefore, they can cause discomfort to patients, can be infection-prone, or require laboratory analysis. Non-invasive techniques are fundamental to patients who frequently take blood tests, or suffer blood loss; these techniques generally exploit the pallor of some body parts to determine whether a patient is anemic or not [12; 13; 14; 15; 16; 17; 18; 19]. Patients who need recurrent blood sampling or who cannot easily move from home can benefit greatly from these techniques and then these approaches are of some importance. Furthermore, the recent trend in healthcare is to treat patients at home as far as possible, through new therapeutic care pathways and services like medical records [20; 21].  
A great effort has been done in recent years to improve non-invasive tool accuracy. Non-invasive devices can be made portable, cheap, and easy-to-use and offer great advantages in rapid pre-diagnosis and self-monitoring. If the devices are low cost, they allow mass screening even in geographic areas with less available economic resources.  
As is already the case in other medical disciplines that can benefit from the extensive use, as an example, of the image analysis, sound or signal analysis and artificial intelligence techniques [22; 23; 24; 25; 26; 27; 28], it is equally important to stimulate research and development of new technologies to deal with anemia. Among other benefits, the reduction of the costs borne by the national health systems and powering the medical and healthcare services can also be considered important.  
Application of non-invasive estimation of anemia in real health care processes could be delayed by divergences between potential interest areas and those dealt with in literature. Marking these divergences can help explore more effective research and experimentation paths to develop and validate the state of the art.  
The Systematic Mapping Study (SMS see Appendix B) [29] has been elected as the optimal approach to probe the NEA literature since it defines a rigorous process for data retrieving and interpretation.  
The paper has the following structure: related work is discussed in Section 2 along with noting the innovative aspects of this work; the method conducted in this mapping study to classify and select papers is described in Section 3; research questions results are analyzed in Section 4; in Section 5 relevant findings from the research results are discussed, and finally conclusions are drawn in Section 6 where possible research directions are also outlined.