Stool Parasite Test (O&P): Symptoms, Results & Guide

What Is the Stool Ova and Parasite (O&P) Examination?

The Stool Ova and Parasite (O&P) examination is a laboratory test that looks for parasites—such as Entamoeba histolytica (amoeba) and Giardia lamblia—and their eggs (ova) in a stool sample. In my clinical practice, I often encounter patients who have been suffering from intermittent diarrhoea, bloating, or unexplained weight loss, only to discover that a microscopic examination of their stool reveals a hidden parasitic infection.

This test is essential for diagnosing gastrointestinal infections acquired through contaminated food or water, especially after travel to regions where these parasites are common.

Why Would My Doctor Order This Test?

Your healthcare provider may recommend a stool O&P examination if you have any of the following symptoms that persist for more than a few days:

• Watery or bloody diarrhoea
• Abdominal cramps and gas
• Nausea or vomiting
• Unexplained fatigue or weight loss
• Low-grade fever with intestinal symptoms

My patients typically describe a pattern of symptoms that come and go, often worsening after meals. If you've recently travelled to developing countries, camped in untreated water areas, or been in contact with children in daycare settings, your risk for parasitic infection increases significantly.

How Is the Test Performed?

Collecting a stool sample at home is straightforward, but there are a few important steps to ensure accurate results:

1. Use a clean, dry container provided by your doctor or lab (avoid urine contamination).
2. Collect a small sample of stool – about the size of a walnut.
3. If possible, collect samples on three different days because parasites are shed intermittently.
4. Refrigerate the sample (do not freeze) and deliver it to the lab within 24 hours.

In some cases, your doctor may ask you to collect a purged stool sample using a mild laxative to increase the yield of parasites.

Reference Ranges and Results

For a healthy individual, the result should show no ova, cysts, or parasites seen. The table below summarises normal findings by age group.

If the report lists a specific organism—such as Giardia lamblia cysts, Entamoeba histolytica trophozoites, or Cryptosporidium oocysts—then you have an active infection that requires treatment.

What Does a Positive Stool O&P Result Mean?

A positive result means that a parasitic organism is living in your intestines and may be causing your symptoms. The most common parasites found in stool samples include:

• Giardia lamblia – causes giardiasis, often with explosive, foul-smelling diarrhoea
• Entamoeba histolytica – causes amoebiasis, which can lead to dysentery and even liver abscess
• Cryptosporidium – causes watery diarrhoea, especially in immunocompromised individuals
• Hookworm ova – associated with iron-deficiency anaemia
• Pinworm eggs – more common in children, causing anal itching

Treatment depends on the specific parasite. For example, metronidazole is often used for giardiasis and amoebiasis, while other infections may require albendazole or nitazoxanide. Your doctor will tailor the therapy to the organism and your overall health.

Can a Stool Parasite Test Be Done During Pregnancy?

Yes, the stool O&P test is safe during pregnancy because it only involves collecting a stool sample. However, treatment of any identified infection must be carefully chosen. For instance, metronidazole is generally avoided in the first trimester unless absolutely necessary. If you are pregnant or breastfeeding, always tell your doctor so they can select the safest treatment options.

How to Prepare for the Stool O&P Test

You do not need to fast or change your diet. However, you should avoid certain medications that could interfere with parasite detection:

• Antacids (especially bismuth subsalicylate)
• Antidiarrhoeal drugs (like loperamide)
• Barium from recent X-ray procedures
• Certain antibiotics

Always inform your healthcare provider about any medications or supplements you are taking.

What Are the Limitations of This Test?

No test is 100% perfect. Because parasites are not always present in every stool sample, your doctor may order three separate samples collected over several days to improve accuracy. Additionally, some parasites (like Cryptosporidium) require special stains or antigen tests for detection. In my experience, repeating the test is often necessary when symptoms are strong but the first sample is negative.

When Should I See a Doctor?

If you have persistent diarrhoea lasting more than a few days, especially with blood, mucous, or weight loss, do not hesitate to contact your healthcare provider. Prompt diagnosis and treatment can prevent complications such as dehydration, anaemia, or spread of infection to others.