Diagnosis of Parasitic Diseases

by CDC

How are parasitic diseases diagnosed?

Many kinds of lab tests are available to diagnose parasitic diseases. The kind of test(s) your health care provider will order will be based on your signs and symptoms, any other medical conditions you may have, and your travel history. Diagnosis may be difficult, so your health care provider may order more than one kind of test.

What kinds of tests are used to diagnose parasitic diseases?

See below for a list of some commonly used tests your health care provider may order.

1. A fecal (stool) exam, also called an ova and parasite test (O&P)

This test is used to find parasites that cause diarrhea, loose or watery stools, cramping, flatulence (gas) and other abdominal illness. CDC recommends that three or more stool samples, collected on separate days, be examined. Your health care provider may request that the lab use special stains to look for parasites not routinely screened for.

This test is done by collection of a stool specimen. Your health care provider may ask you to put your stool specimen into a special container with preservative fluid. Specimens not collected in a preservative fluid should be refrigerated, but not frozen, until delivered to the lab or the health care provider's office. This test looks for ova (eggs) or the parasite.

2. Endoscopy

Endoscopy is used to find parasites that cause diarrhea, loose or watery stools, cramping, flatulence (gas) and other abdominal illness. This test is used when stool exams do not reveal the cause of your diarrhea. This test is a procedure in which a tube is inserted into the mouth or rectum so that the doctor, usually a gastroenterologist, can examine the intestines. This test looks for the parasite.

3. Blood tests

Some, but not all, parasites can be found by testing your blood. Blood tests look for a specific parasite infection; there is no blood test that will look for all parasitic infections. There are two general kinds of blood tests that your doctor may order:

a. Serology

This test is used to look for antibodies or for parasite antigens produced when the body is infected with a parasite and the immune system is trying to fight off the invader. This test is done by your health care provider taking a blood sample and sending it to a lab. This test is able to detect antibodies produced by the body or antigen from the parasite found in your blood.

b. Blood smear

This test is used to look for parasites that are found in the blood. By looking at a blood smear under a microscope, parasitic diseases such as malaria, filariasis, or babesiosis, can be diagnosed. This test is done by placing a drop of blood on a microscope slide. The slide is then looked at under a microscope.

4. X-ray, Magnetic Resonance Imaging (MRI) scan, Computerized Axial Tomography scan (CAT)

These tests are used to look for some parasitic diseases that may cause swelling of internal organs or abnormal scarring.

Can my lab work be sent directly to CDC?

No. CDC is a reference lab for the 50 states. This means that CDC cannot accept specimens unless they are sent by your state health lab.

Where should lab specimens be sent for testing?

It is best to send stool specimens to a lab with experience, such as the local, county, or state health lab, a commercial lab, or a hospital lab. Diagnosis of any stool parasite may be difficult; by submitting several stool specimens, your chance of being diagnosed correctly is higher than by submitting just one sample. If you receive a negative lab report, your physician may choose to send another sample to a different lab for confirmation. Blood testing is done by a variety of labs.

Is it true that labs in the United States cannot diagnose parasites?

No. Labs throughout the United States are qualified to diagnose parasitic infections.

About the Author

www.cdc.gov
The Centers for Disease Control and Prevention (CDC) is one of the 13 major operating components of the Department of Health and Human Services (HHS), which is the principal agency in the United States government for protecting the health and safety of all Americans and for providing essential human services, especially for those people who are least able to help themselves.