Table 4.

Differences in circulating cytokines levels between patients with tension-type headache and healthy controls

Cytokine	N of studies	Total participants	Std. Mean Difference (95% CI) Effect Estimate	P Value	I2
IL-2	2	187	-5.48 (-14.13, 3.17)	0.21	99%
IL-8	3	242	1.08 (-1.02, 3.18)	0.31	98%
TGF-β	2	168	0.52 (0.18, 0.86)	0.003	0%
TNF-α	2	165	0.64 (0.33, 0.96)	0.0001	0%

Abbreviations: CI Confidence interval, I² Measure of heterogeneity, IL-2 Interleukin-2, IL-8 Interleukin-8, TGF-β Transforming growth factor β, TNF-α Tumor necrosis factor alpha