Lymphogranuloma venereum can be extremely difficult to test for. To come to a correct diagnosis, doctors have to be both familiar with the illness and take a very careful medical history. Simply examining the sores may not give a clear result, since bacteria may not always be visible depending on the stage of the illness.
Because Lymphogranuloma venereum is caused by a type of chlamydia, testing sores and inflamed lymph nodes for the presence of chlamydia can lead to a correct diagnosis. Most labs are not capable of distinguishing between a standard genital chlamydia infection and Lymphogranuloma venereum, so the infection may end up being misdiagnosed. Still, treatment for each situation is similar, and in the presence of a bubo-containing chlamydia, it's a pretty safe bet that Lymphogranuloma venereum is the culprit rather than a standard genital strain.
Sources:
McLean CA, Stoner BP, Workowski KA. "Treatment of lymphogranuloma venereum." Clin Infect Dis. 2007 Apr 1;44 Suppl 3:S147-52.
