# A Systematic Mapping Study on Research in Anemia Assessment with Non-Invasive Devices
## 5 Discussion  
This paper has analyzed how non-invasive anemia assessment develops, has assessed the results obtained from different points of view, recognized some shortcomings in the literature, and gave ideas for future research. The following results are the result of the careful analysis of the generated data maps that led to answering the research questions listed in Table 1.  
(RQ1) As seen in Section 4.1 the total number of researches relative to non-invasively estimating anemia seems to remain approximately stable over the years. Section 4.1 also highlights a trend that varies from area to area, and seems to be increasing in the most populated countries and fast-growing economies, where anemia is a particularly felt problem or cost-saving objectives are particularly pursued.  
(RQ2) Figure 5 shows that most studies refer to health facilities while a good part refers to device manufacturers and Health Insurance Companies/National Health System, with very few studies addressing doctors, caregivers, and citizens.  
(RQ3) The great majority of the papers investigate different regions of interest and different types of non-invasive devices. As seen in Figure 14, the most discussed device is the co-oximeter and the finger as ROI; camera devices follow and are used to examine different ROIs, but the conjunctiva seems to be the most promising one among the others.  
(RQ4) As already told in Section 4.5 there is a predominance of papers that propose a solution, followed by a good number of empirical evaluations and validations, suggesting that the majority of the researchers try to find and evaluate new solutions and technologies to further improve the anemia assessment by making it faster and simpler.  
(RQ5) The literature demonstrates its effectiveness through empirical evidence, therefore most of the papers were categorized as \"empirical\" (see Figure 8). The overall empiricism exhibits a deep analysis of explored arguments. Few publications express an opinion or review existing technologies.  
(RQ6) Different kinds of devices are proposed as a solution; they are driven by different technologies, thus making them suitable or not to certain situations.  
The most common solution is to use light absorption and reflection properties through co-oximeters. These devices can distinguish oxyhemoglobin and deoxyhemoglobin measuring the absorption of light passing through blood, light that is often emitted by a finger clamp that shines it through the fingertip. However, it must be specified that using oxygen saturation of hemoglobin is an indirect way to evaluate hemoglobin itself thus its values can be influenced by external factors that can alter the oxygen availability in the blood or blood circulation such as respiratory failure; also available outside health facilities the device has good accuracy but it can be influenced by some external factors such as skin tone [6].  
Another solution discussed by a considerable number of papers is to use a digital camera to take photos or small videos to a body part (conjunctiva, retina, sclera, fingernail) to later analyze it and provide information to the user. The solution is advantageous because it only needs common devices to be used but it has the disadvantage of being a two-step process (take a photo and analyze it); furthermore, taken photos can be largely biased by light conditions, so particular attention has to be played in the acquisition phase [12; 13].  
An alternative to the camera solutions is smartphone-based, which have the great advantage of local analysis of the taken photo that quickens the diagnosis process. Smartphone-based solutions are designed to be used by anyone and can embed tools that go further to the lone measurement.  
Both camera and smartphone solutions have to face the problem of variable light conditions that greatly influence the shots and therefore the diagnosis outcomes. Hence camera adapters that artificially illuminate the ROI have been proposed [14; 15; 16].