Are the 5-HIAA test and the serotonin test conclusive for detecting a carcinoid tumor?

It is not 100% certain. In fact, the urine 5HIAA test will miss 50% of cases. Therefore other tests are usually done in conjunction with these tests. Among the most common tests done for diagnostic purposes are blood serotonin and blood chromogranin A. Other tests such as substance P and VIP may also be done.