It will dep on the parasite. Stools are very unreliable my were always negative for Ascaris. After I done the blood test it showed that my eosinophils (specific white blood cells) were extremely high. They stand-by and hunt down larger parasites such as roundworms, etc. And become very active during ascariasis infection. Endoscopy or colonoscopy can be effective but you still need to ID the parasite type and it's still can be hit or miss.