Error in meta-analysis regarding plasma IL-6. Ellen Generaal, GGZingeest/VU University Medical Center 30 May 2014 In this meta-analyses, Uceyler et al. state as one of their main findings that fibromyalgia patients had higher plasma levels of IL-6 than controls. For this result, they refer to Table 4, which should be Table 9 (findings from meta-analysis are only shown in Table 9). The presented data (SMD[95%CI] = -0.34 [-0.64, -0.03]) shows that their conclusion is incorrect: mean plasma IL-6 levels of controls are higher than the values for fibromyalgia patients. The three studies that were examined in this analysis (Togo, 2009; Schwarz, 2002; Bazzichi, 2007) show similar data as presented in Table 9. Thus, although perhaps unexpected, the conclusion should be that fibromyalgia patients had lower plasma levels of IL-6 than controls. Subsequently, in the discussion, authors should have explained why results of plasma IL-6 differ between their systematic review and the meta-analyses. Also, the same caveats should have been made as the authors partly do now: the conclusion is based on only three studies, there are differences in assessment methods, basal cytokine levels show variability and circadian rhythmicity, and the impact of lifestyle and disease was not taken into account (Generaal et al., Pain, 2014). Competing interests There are no competing interests.