Diagnosis

If you have diarrhea and related symptoms, the cause may be difficult to diagnose. Even if blastocystis is found in your stool, it might not be causing your symptoms. Often another food- or water-borne organism is the likely cause of illness.

Your doctor will take your medical history, ask you about recent activities, such as traveling, and perform a physical exam. A number of lab tests help diagnose parasitic diseases and other noninfectious causes of gastrointestinal symptoms:

• Stool (fecal) exam. This test looks for parasites. Your doctor might give you a container with preservative fluid for your stool sample. Refrigerate — don't freeze — your samples until you take them to your doctor's office or lab.
• Endoscopy. If you have symptoms, but the fecal exam doesn't reveal the cause, your doctor might request this test. When you're under sedation, a special camera on a tube is used to exam your digestive tract.
• Blood tests. A blood test that can detect blastocystis is available but not commonly used. However, your doctor might order blood tests to look for other causes of your signs and symptoms.