The patient used an EZ Detect fecal occult blood test. The test was positive. She saw a tiny blue circle on the piece of paper indicating trace of blood in her stool. But, she indicated there was also urine in the toilet bowl. Would urine affect this test?
After doing some research on the issue, including contacting the company "Biomerica" and finding on the Internet the "Physician's Instruction Pamphlet" I did find that urine does affect such tests. The mentioned pamphlet states: 1) Urinate first and then flush the toilet; 2) Have a bowel movement; 3) carefully drop a test tissue into the toilet bowl, etc. Thus, Biomerica is adament that for the test to be reasonably accurate urine should be absent from the toilet bowl. They also confirmed the same by email.
One should keep in mind that even if you take all those precautions you should understand that such tests are not "accurate" especially when they are positive. This is due to such tests having a rather low sensitivity (true positive rate) combined with a disease that has a fairly low prevalence rate. Quoting Wikipedia on fecal occult blood test with a positive result: "about 2-10% have cancer, while 20%-30% have adenomas." Depending on one's circumstances those statistics can vary (age, sex) and increase a bit. But, still a positive test result still leaves one much more likely to be free of colon cancer. It is just an information piece that may suggest further test investigation may be warranted (colonoscopy, etc.).
In view of the above, following Biomerica's instructions I would not consider a positive test result with urine in the bowl as counting as a true positive test. Instead, I would continue testing with the remaining test tissues and make sure I follow the appropriate protocol as indicated above. If one would feel they did not have enough remaining test tissues, I would just get another set and re-test again. If the individual does test negative three times in a row that should give her much comfort. The test is far more accurate on "negatives" vs. "positives" because the test's specificity (true negative rate) is much above its sensitivity (true positive rate).