Moreover, PPBP has also been identified as a biomarker for other diseases, such as cancers (e.g. gastric cancer (Chen et al., 2022) and thyroid carcinoma (Zhang et al., 2021b)), inflammation (e.g. rheumatoid arthritis (Guerrero et al., 2021)), neurosyphilis (Li et al., 2020), COVID-19 (Yatim et al., 2021), and metabolic disease (e.g. diabetes mellitus (Moin et al., 2021; Zhang et al., 2021a)). Here, PPBP is linked to COVID-19.