This is in relation to the study of Neuwinger et al. in 2019 entitled, "Underfilling of vacuum blood collection tubes leads to increased lactate dehydrogenase activity in serum and heparin plasma samples". They included a category of the parameters considering matrix effect aside from the filling effect. I have searched for the definition of matrix effect but I would like to further learn about it and its mechanism in general and for LDH, specifically.