[Cut-off values and grey-zone of tumor markers in blood]

Cut-off values and grey-zone of tumor markers in blood were described. Cut-off values are a little different from reference intervals, and can discriminate tumor status from non-tumor status. Cut-off values are commonly determined by ROC (receiver operating characteristic) curve, that can show us the diagnostic efficiency of the test. The patients of control group used in ROC curve must be selected from benign diseases whose conditions are similar to those of tumors. Grey-zone is defined as the range between cut-off value from healthy subjects and that from benign diseases. Cost-efficiency must be considered when cut-off values and grey-zone of tumor markers in blood were set up.