A blood sample can also be tested for evidence of infection. Blood tests are indicated for travelers or immigrants from endemic areas who have not been treated (or not treated appropriately) in the past. The most common tests detect antibodies to the adult worm. For accurate results, the blood sample tested should be collected at least 6 to 8 weeks after likely infection. Blood testing may not be appropriate for patients who have been repeatedly infected and treated in the past because antibodies can persist despite cure. In these patients, blood testing cannot distinguish between a past or current infection. A specific blood test has been developed for this population (which can detect an active infection based on the presence of schistosomal antigen), but this test is not commercially available in the United States and is currently being studied for its ability to detect mild infections.