The standard maximum volumes that could be extracted differ for the procedures: 140 ml for QIAgen; 100 ml for MagNA Pure; 50 ml for KingFisher; and, 200 ml for easyMag. The effect of using these manufacturers' recommended volumes for stool suspensions was not evaluated in the present study, although to have done so would have meant that depending on the procedure used, there would have been a 2 to 4 fold increase in the amount of endogenous inhibitors in the starting volume without a concomitant increase in the extraction, washing and elution buffer volumes. Others have shown that increasing the starting volume increased the co-extraction of inhibitors [21, 25, 26] and that the final rRT-PCR outcome is a balance between specific template and coextracted inhibitors [27] .