Review: Non-invasive blood haemoglobin level measurement

Blood haemoglobin level measurement is an essential part of a global attempt at reducing anaemia. This review is to elaborate on current advancements in non-invasive methods to measure blood haemoglobin level. This review also elaborates on current established invasive methods for measuring blood haemoglobin level and its role as a reference standard. This review also maps the wavelength used for non-invasive blood haemoglobin level measurement to our observation on blood haemoglobin level control. The research team has obtained Journal or proceeding articles from Google Scholar and Scopus using the keyword "non-invasive haemoglobin" within its titles from 1980 to 2020. The team has grouped the articles by non-invasive methods, invasive reference methods, and the wavelength used by those methods. There are 128 articles gathered from the keywords. There are 88 articles included in this study. There are 26 light source wavelength combinations that the developers use for non-invasive blood haemoglobin level. Most of the wavelength fits neatly in the window between 500 nm to 1000 nm, where the blood-haemoglobin-level control absorbance is low. The researcher has gathered 13 different non-invasive methods for measuring blood haemoglobin level and those commercially available. Most of the articles we have gathered are unregistered trials, and the majority of methods are unproven. We are taking this as a research limitation. The researchers should conduct a further trial for each method listed.