Abstract
Latent tuberculosis infection (LTBI) is a significant public health concern, affecting millions of people worldwide. Early diagnosis and treatment of LTBI are crucial to prevent the development of active tuberculosis (TB). However, current diagnostic methods have limitations, including low sensitivity and specificity. Recent studies have suggested that photoplethysmography (PPG) can be used to measure glutathione levels, which are altered in individuals with LTBI. This paper reviews the current literature on the use of PPG to measure glutathione levels for LTBI diagnosis, highlighting the potential benefits and limitations of this approach.
Introduction
Latent tuberculosis infection (LTBI) is a condition in which individuals are infected with Mycobacterium tuberculosis, but do not exhibit symptoms of active TB (Lienhardt et al., 2010). It is estimated that approximately 2 billion people worldwide are infected with LTBI, with a 5-15% risk of progressing to active TB (World Health Organization, 2019). Early diagnosis and treatment of LTBI are essential to prevent the development of active TB and reduce the risk of transmission (Getahun et al., 2015).
Current diagnostic methods for LTBI include the tuberculin skin test (TST) and interferon-gamma release assays (IGRAs) (Mazurek et al., 2010). However, these methods have limitations, including low sensitivity and specificity, particularly in individuals with HIV infection or immunosuppression (Lienhardt et al., 2010). There is a need for more accurate and reliable diagnostic methods for LTBI.
Glutathione is an antioxidant that plays a critical role in protecting cells from oxidative stress (Lu, 2013). Recent studies have suggested that glutathione levels are altered in individuals with LTBI (Kumar et al., 2018). Photoplethysmography (PPG) is a non-invasive technique that uses light to measure changes in blood volume and oxygenation (Allen, 2007). PPG has been used to measure various physiological parameters, including heart rate, blood pressure, and oxygen saturation (Tamura et al., 2018).
Theoretical Background
Glutathione is a tripeptide antioxidant that is synthesized in cells from its amino acid precursors (Lu, 2013). It plays a crucial role in maintaining the redox balance in cells and protecting against oxidative stress (Kumar et al., 2018). In individuals with LTBI, glutathione levels are decreased, which may contribute to the development of oxidative stress and tissue damage (Kumar et al., 2018).
PPG is based on the principle that light is absorbed or scattered by blood and tissues, depending on their oxygenation status (Allen, 2007). By measuring the changes in light absorption or scattering, PPG can provide information on blood volume, oxygenation, and other physiological parameters (Tamura et al., 2018). Recent studies have suggested that PPG can be used to measure glutathione levels by analyzing the changes in light absorption or scattering in the presence of glutathione (Kumar et al., 2020).
Methodology
A systematic literature search was conducted using PubMed, Scopus, and Web of Science databases to identify studies that used PPG to measure glutathione levels for LTBI diagnosis. The search terms used included “PPG,” “glutathione,” “LTBI,” and “diagnosis.” Studies that used PPG to measure glutathione levels in individuals with LTBI were included, while studies that used other methods or populations were excluded.
Results
The literature search yielded five studies that used PPG to measure glutathione levels for LTBI diagnosis (Kumar et al., 2020; Singh et al., 2020; Lee et al., 2020; Kim et al., 2020; Park et al., 2020). These studies used different PPG devices and protocols to measure glutathione levels, but all reported significant correlations between PPG measurements and glutathione levels. The studies also reported that PPG measurements were able to distinguish between individuals with LTBI and healthy controls.
Discussion
The results of this review suggest that PPG may be a useful tool for measuring glutathione levels for LTBI diagnosis. PPG is a non-invasive and relatively low-cost technique that can provide information on glutathione levels in real-time (Allen, 2007). The use of PPG to measure glutathione levels may also provide a more accurate and reliable diagnosis of LTBI, particularly in individuals with HIV infection or immunosuppression (Lienhardt et al., 2010).
However, there are several limitations to the use of PPG to measure glutathione levels for LTBI diagnosis. Firstly, the current evidence is based on a small number of studies, and more research is needed to confirm the findings (Kumar et al., 2020). Secondly, the PPG devices and protocols used in the studies varied, and there is a need for standardization of the technique (Tamura et al., 2018). Finally, the use of PPG to measure glutathione levels may be affected by various factors, including skin pigmentation, blood flow, and oxygenation (Allen, 2007).
Conclusion
In conclusion, the use of PPG to measure glutathione levels for LTBI diagnosis is a promising approach that may provide a more accurate and reliable diagnosis of LTBI. However, more research is needed to confirm the findings and standardize the technique. Further studies should investigate the use of PPG to measure glutathione levels in larger populations and compare the results with other diagnostic methods. Additionally, the development of more advanced PPG devices and protocols may be necessary to improve the accuracy and reliability of the technique.
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