Receiver operating characteristics curves of HE4 for differentiating chronic kidney disease patients from healthy control subjects. The area under the curve of S-HE4, U-HE4 and R-HE4 are 0.984, 0.399 and 0.972, respectively. HE4, human epididymis protein 4; S-, serum; U-, urine; R-HE4, ratio of urinary-to-serum HE4 level.