PTH and anemia (phenotype): The presence of hearing impairment in MHD patients was a dependent variable (0 = none, 1 = yes), while gender (0 = male, 1 = female), diabetes mellitus (0 = none, 1 = yes), hyperuricemia (0 = none, 1 = yes), anemia (0 = none, 1 = yes), hypoalbuminemia (0 = none, 1 = yes), blood potassium (0<5.3mmo/l, 1≧5.3mmo/l), blood calcium (0<2.52mmol/l, 1≧2.52mmol/l), blood phosphorus (0<1.51mmol/l, 1≧1.51mmol/l), PTH (0<300pg/ml, 1≧300pg/ml), FGF23 (0<132pg/ml, 1≧132pg/ml), and D-serine (0<10μM, 1≧10μM) as independent variables.