Since 2003, our Laboratory has offered fecal antigen testing for giardia and crytptosporidium intestinal parasites. While performing well, these tests -- which address the two most common parasite pathogens in our patient populations -- have been underutilized. Compared to these antigen tests, approximately three times as many routine microscopic ova and parasite exams by microscopy were conducted in 2005, but with a lower rate of pathogen detection.

Except for eight blastocystis hominis -- which are of doubtful significance -- giardia and cryptosporidium were the only significant intestinal parasites identified in 2005 by routine ova and parasite microscopy. Routine ova and parasite microscopy did not reveal any important organisms, and is the most time-consuming and least beneficial procedure performed in microbiology in our Lab and most labs. Cryptosporidium -- which resists common municipal water treatment methods -- is relatively common, but difficult to discern by microscopy due to its small size, making the antigen test more sensitive. Giardia is the only other parasite to which exposure is likely without foreign travel. The antigen test is also more sensitive than microscopy for giardia.

To increase the chances of finding a significant organism, routine ova and parasite exam is not offered without being preceded by giardia and cryptosporidium antigen testing. All routine requests for intestinal parasite studies have the antigen tests performed. Frequently -- by the time the antigen test is completed -- the diarrhea will have ended or the cause of the diarrhea or abdominal complaint is identified, and a complete ova and parasite microscopic exam will no longer be desired, but is still obtainable by calling the Laboratory at 314.653.5940. The specimen jars will be held one week for this possibility. Many hospitals have adopted similar policies. They find it unnecessary to perform routine, complete microscopic ova and parasite exams frequently. Recent foreign travel or unexplained eosinophilia is an indication for a routine ova and parasite exam. This test is ordered as "ova and parasite screen."

Giardia