In what way does crohn's disease alter test results?false positives or false negatives?

Not usual: Crohn's disease can alter some test due to nutritional problems or bleeding but other no. False positive means that a test comes up positive but there is no disease present. False negative means a test is negative but disease is present. These are statistical number calculated for each test for a disease.

Too open ended: We cannot answer the question without further consideration of the type of tests you are referring to. There are definitely some tests that can be falsely elevated if you have crohn's disease. The one that comes to mind is the blood test for celiac disease (ttg) which can be elevated in crohn's. But you cannot make a blanket statement about all tests. Sorry.