HPRT1 and systemic inflammatory response syndrome: In validation set granulocytes, expression of INSM1 was undetectable by QGP, and only half of the samples yielded a signal above the limit of detection for LY6G6E. The other two candidate reference genes, RAB2A and YTHDF3, showed significant 1.5- and 1.3-fold higher mean expression levels, respectively, in sepsis than in SIRS (Figure 5A), as did the known reference genes HPRT1 (2.6-fold), GUSB (3.2-fold), PPIB (1.5-fold), and GAPDH (2.9-fold) (Figure 5B).