Progressive evaluation in spectroscopic sensors for non-invasive blood haemoglobin analysis—a review

Objective.Frequent monitoring of haemoglobin concentration is highly recommended by physicians to diagnose anaemia and polycythemia vera. Moreover, other conditions that also demand assessment of haemoglobin are blood loss, before blood donation, during pregnancy, and preoperative, perioperative and postoperative conditions. The cyanmethemoglobin/haemiglobincyanide method, portable haemoglobinometers and haematology analyzers are some of the standard methods used to diagnose the aforementioned ailments. However, discomfort, delay and risk of infection are typical limitations of traditional measuring solutions. These limitations create the necessity to develop a non-invasive haemoglobin monitoring technique for a better lifestyle.Approach.Various methods and products have already been developed and are popular due to their non-invasiveness; however, invasive solutions are still considered as the reference standard method. Therefore, this review summarizes the attributes of existing non-invasive solutions. These attributes are finalized as brief details, accuracy, optimal benefits and research challenges for exploring potential gaps, advancements and possibilities to consider as futuristic alternative methodologies.Main results.Non-invasive total haemoglobin assessment techniques are mainly based on optical spectroscopy (reflectance/transmittance) or digital photography, or spectroscopic imaging in spot-check/continuous monitoring mode. In all these techniques, we have noticed that there is a need to consider different light conditions, motion artefacts, melanocytes, other blood constituents, smoking and precise fixing of the sensor from the sensing spot for exact formulation.Significance.Moreover, based on careful and critical analysis of outcomes, none of these techniques or products are used independently or intended to replace invasive laboratory testing. Therefore, there is a requirement for a more accurate technique that can eliminate the requirement for blood samples and likely end up as a reference standard method.