In COVID-19, when the proportion of monocytes was less than 6 %, high expression of SERPINA3, SAA1, and SAA2 indicated a higher risk; conversely, when the proportion of monocytes was greater than 6 %, low expression of SERPINA3 and SAA2 and high expression of SAA1 indicated a higher risk (Fig. 6B); in Mix, high expression of SERPINA3, SAA1, and SAA2 indicated a higher risk (Fig. 6C). Here, SAA1 is linked to COVID-19.