The cause of your diarrhea may be difficult to diagnose. Even if blastocystis is present on a fecal exam, it may not be causing your symptoms.

Your doctor likely 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 or their eggs (ova). Your doctor may give you a special container with preservative fluid for your stool samples. 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 may request this test. After you're sedated, a doctor, usually a gastroenterologist, inserts a tube into your mouth or rectum to look for the cause of your symptoms. You'll need to fast beginning the night before the test.
  • Blood tests. A blood test that can detect blastocystis is now available, but it isn't commonly used. However, your doctor may order blood tests to look for other causes of your signs and symptoms.