ABCG2 and chronic kidney disease: The results listed in Table 2 showed the differences in the occurrences of CKD stage = 1 and those in group CKD stage≥2 were statistically significant regarding genotypes of ABCG2 gene polymorphism (P < 0.001 and P = 0.026); whilst the difference was not statistically significant in group CKD stage≥3.