What Foods Can Cause a Positive Cologuard Test?

November 15, 2025 •

4 min read

According to the official Cologuard instructions, no special preparation or dietary changes are needed before taking the test. This means the question of what foods can cause a positive Cologuard test is based on a common misconception, as food and drink will not affect the results.

Quick Summary

This article explains why dietary restrictions are unnecessary for Cologuard, unlike older stool tests. It clarifies that a positive result is not influenced by food intake but can be caused by other factors like bleeding hemorrhoids.

Key Points

No Dietary Restrictions: Food and drink do not cause a positive Cologuard test because its advanced technology targets human-specific DNA and hemoglobin.
Confusion with Older Tests: The misconception about diet and stool tests arises from older methods like the gFOBT, which are sensitive to dietary compounds.
Cologuard Technology: The test's multi-target stool DNA technology is what makes it unique and unaffected by dietary changes.
Positive Result Factors: A positive result is not a cancer diagnosis but can indicate altered DNA or blood from sources like hemorrhoids, diarrhea, or menstruation.
Follow-up is Key: Any positive Cologuard result requires a diagnostic colonoscopy for definitive answers, regardless of potential false-positive causes.
Accuracy vs. Colonoscopy: While highly effective for cancer detection, Cologuard is less accurate at finding precancerous polyps than a colonoscopy.

Cologuard vs. Older Stool Tests: Why the Confusion?

Many people incorrectly assume that dietary restrictions apply to the Cologuard test because they are required for older, less advanced stool screening methods. The confusion primarily stems from the guaiac-based Fecal Occult Blood Test (gFOBT), which is designed differently and is sensitive to substances found in certain foods and supplements. The Cologuard test, however, uses more advanced technology, which eliminates the need for any diet modification.

How Cologuard Works Without Dietary Restrictions

The Cologuard test is a multitarget stool DNA test that analyzes your stool for both altered DNA markers and microscopic amounts of blood (hemoglobin). Unlike the chemical-reaction-based gFOBT, Cologuard's sophisticated technology specifically targets human DNA and human hemoglobin, making it unaffected by compounds from food. The test's dual-marker approach increases its accuracy for detecting colon cancer and precancerous polyps compared to other stool tests. Because of this, you can eat your regular meals and take your normal medications right up until you collect your sample.

Potential Causes of a Positive Cologuard Result

Since food is not a factor, what else could trigger a positive result? It's important to remember that a positive Cologuard result is not a diagnosis of cancer. It simply means that altered DNA or blood was detected in the sample, and a follow-up colonoscopy is necessary. The source of the blood or DNA could be a number of things. One of the most common causes of a false positive is a non-cancerous condition that causes bleeding in the digestive tract. These include:

Hemorrhoids: These can cause rectal bleeding and lead to a positive test result. For this reason, it's advised not to collect a sample if you have active bleeding hemorrhoids.
Diarrhea: An acute illness involving diarrhea can disrupt the intestinal lining and may cause a positive result. It is best to wait until your bowel movements have returned to normal before testing.
Menstruation: Women who are menstruating should wait to take the test until their period is over to avoid a false positive due to blood contamination.
Other conditions: Inflammatory Bowel Disease (IBD), ulcerative colitis, and other conditions that cause intestinal bleeding can also lead to a positive result.

Comparison of Stool-Based Screening Methods

Understanding the differences between the various types of colorectal cancer screening tests can help clarify why some require diet prep while Cologuard does not. The following table compares Cologuard with the older gFOBT and the gold-standard colonoscopy.


Feature	Cologuard (Stool DNA Test)	gFOBT (Guaiac-based FOBT)	Colonoscopy
Dietary Prep	No restrictions required.	Dietary restrictions apply (e.g., no red meat, Vitamin C).	Requires a full bowel preparation.
Test Method	Analyzes DNA and blood (hemoglobin) in stool.	Detects blood (heme) via a chemical reaction.	Visual examination of the entire colon.
False Positive Rate	Approximately 12-14%.	Susceptible to false positives from food and medication.	Low, but prep issues can affect results.
Polyp Detection	Detects 42% of large precancerous polyps.	Lower detection rate for polyps.	Detects 95% of large polyps.
Follow-up for Positive Result	Requires a diagnostic colonoscopy.	Requires a diagnostic colonoscopy.	Polyps can be removed during the procedure.

What to Do After a Positive Result

If you receive a positive Cologuard result, the most important next step is to follow up with your healthcare provider to schedule a diagnostic colonoscopy. A positive result is not a final diagnosis, but rather an indication that further investigation is needed. In fact, nearly 40% of people with a positive Cologuard test have a normal colonoscopy result. While this can cause anxiety, a colonoscopy is the only way to get a definitive answer and, if necessary, remove any polyps or cancerous growths found during the procedure.

Conclusion

The Cologuard test is a modern screening method designed for ease of use, including the elimination of dietary restrictions. While the idea that certain foods can cause a positive result is common, it is a misunderstanding based on the requirements of older, traditional stool tests. Cologuard's advanced technology specifically targets human DNA and blood markers, ignoring any dietary influence. A positive test, while it can be caused by non-cancerous factors like hemorrhoids or menstruation, always necessitates a follow-up colonoscopy to confirm a diagnosis and take appropriate action. By understanding how Cologuard works, you can approach your screening with confidence and clarity, free from unnecessary dietary concerns. The key to accurate results is to follow the kit's specific instructions, particularly regarding active bleeding, and to always complete a diagnostic colonoscopy after a positive result. For more information, consult the official Cologuard website and your healthcare provider.

Official Cologuard Website

Frequently Asked Questions

No, you do not need to change your diet before a Cologuard test. Unlike older stool tests, Cologuard's technology is not affected by food or drink.

No, eating red meat will not cause a false positive Cologuard test. This restriction applies only to older, guaiac-based fecal occult blood tests (gFOBT).

The confusion stems from the requirements of older tests like gFOBT, which required avoiding red meat, certain vegetables, and supplements before testing. People often assume the same rules apply to Cologuard.

A positive result can be caused by the detection of altered DNA or blood from various sources, including precancerous polyps, cancer, or non-cancerous conditions like hemorrhoids, diarrhea, or menstruation.

Yes, a diagnostic colonoscopy is the necessary and only recommended next step after a positive Cologuard result. It is the only way to get a definitive diagnosis and, if needed, remove polyps.

No, iron supplements do not cause a false positive Cologuard test. This is another restriction that only applies to older stool tests like gFOBT.

While Cologuard is highly effective at detecting cancer, a colonoscopy is considered the gold standard and is more sensitive at detecting precancerous polyps.