Hello and thanks for the query.
Crohn's disease is a difficult condition to diagnose since the symptoms can point towards a variety of different conditions. At first, the symptoms can begin as subtle and vague. Over time, the symptoms may become more severe and indicative of Crohn's disease. Sometimes, patients will not receive an accurate diagnosis for years.
Of all possible tests, a colonoscopy is the most effective, since the condition may be in parts of the bowel that are difficult to otherwise examine.If only the ileum is affected, Crohn's disease cannot be diagnosed through a colonoscopy. Blood tests can help doctors achieve an accurate and thorough diagnosis. Anemia that is caused by a management of crohn's disease.
 Antibodies to various proteins including Baker's or Brewer's yeast (saccharomyces cerevisiae) and bacteria like Escherichia. coli (E. coli) are present in the blood of many people with Crohn's disease but rarely in normal people. 
The blood tests currently available are anti-ASCA, anti-OmpC, and anti-CBir1 flagelin antibodies.But these tests are not done in all laboratories.

ASCA is anti-saccharomyces cerevisiae antibody. Saccharomyces cerevisiae is Brewer's or Baker's yeast. Crohn's patients have a high prevalence of abnormal antibodies to this yeast. 
 OmpC is the abbreviation for an antibody that develops in many Crohn's patients to the outer membrane porin protein of the bacteria E. coli though that bacteria is not thought to be the cause of Crohn's disease.
 Just recently Prometheus Laboratories added antibody testing for a specific protein on bacteria that constitutes the flagelin or hair like structure on certain bacteria enabling movement and attachment of bacteria in the intestine called CBir1 flagelin.

The mainstay for the diagnosis of crohn's however is colonoscopy along with biopsy.
The blood tests are relatively very new and not being done everywhere.
I hope to have answered your query however you may revert to  me or any other query.
Best of luck.
Thanks

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