Table 2. Association between the rs3845446 A/G SNP and perioperative fentanyl use in the preliminary and confirmatory study.

	Genotypes	Numbers	Perioperative fentanyl use (Median)	p-value
Preliminary study	AA	46	6.80	0.032
	AG	41	6.83
	GG	13	5.06
Confirmatory study	AA	122	8.00	0.033
	AG	107	7.05
	GG	26	6.61

p-values were calculated using Kruskal-Wallis test.