Postmortem interval, agonal state, and tissue pH have all been found to weakly correlate with RNA quality (Barton et al., 1993; Harrison et al., 1995; Johnston et al., 1997; Li et al., 2004; Tomita et al., 2004). In addition to reducing RNA quality, prolonged agonal states and low tissue pH can lead to differences in the representation of certain transcripts (Harish et al., 2013; Li et al., 2004; Lipska et al., 2006). For instance, patients who suffered from prolonged agonal states had lower tissue pH and decreased expression of specific genes, especially those involved in energy metabolism and proteolytic activities (Harish et al., 2013; Li et al., 2004). Increased expression of genes encoding stress-response proteins and transcription factors has also been observed in patients with prolonged agonal states and low pH (Li et al., 2004). The correlation between changes in expression and these variables thus appears to be transcript specific rather than an overall degradation of RNA (Harish et al., 2013). Several precautions should be taken to reduce confounding factors that impact RNA quality. For example, it has been suggested
