Can cancer urine test reagents really detect cancer?

What you said is possible. None of the reagents for detecting cancer urine can reach the accuracy of 100%. Usually there are many interference items in the test, which leads to inaccurate test results. There may be some false positive or false negative results. Generally, the reason for these situations may be that urine samples contain hematuria, proteinuria, occult blood, bilirubin and urine urobilinogen, which may cause false positives. If there are people with cancer diagnosis, and cancer patients who have undergone effective treatment (including chemotherapy, radiotherapy and surgical resection), the urine test will also appear false negative.