Stool Tests: What Do Positive and Negative Results Mean?

Regarding stool examination?

Hello, doctor.
Recently, I sought treatment at a nearby clinic due to the flu and took medication for a few days.
Later, I experienced difficulty with bowel movements, so I returned for a follow-up.
The doctor checked my records and noticed that I had not undergone colorectal cancer screening, so I was advised to do so and brought home two glass vials.
I was unsure why there were two vials since my wife only received one during her screening.
I later learned that two types of tests were conducted: one using a chemical method and the other using an immunochemical method.
The result for the chemical method was positive (+), indicating a positive reaction, while the immunochemical method result was negative (-), indicating a negative reaction.
The doctor analyzed that my intestines were normal, but there was a slight positive reaction for occult blood in my stomach, and he recommended a referral to a larger hospital for further examination (I am unclear if stool screening can differentiate between the stomach and intestines).
However, I am a bit confused about why both types of screening were performed simultaneously, and what the inconsistent results signify.
Do I need to undergo further testing? I wonder if the larger hospital will require me to have an endoscopy and colonoscopy.
Additionally, I informed the doctor that I do not have stomach pain, abdominal pain, or any discomfort, and I have never had any gastrointestinal diseases.
Yet, strangely, the doctor noted "R019 Abdominal Pain" and "K2971 Gastritis with Hemorrhage" in the referral diagnosis, even though I do not have these symptoms.
I am unsure why this was written.
Currently, my bowel movements have returned to normal, and I have recovered from the flu.
I would appreciate your response.
Thank you.

Ong Picton, 60~69 year old female. Ask Date: 2019/12/02

Dr. Chen Shidian reply Gastroenterology and Hepatology

The immunological method is more accurate as it specifically tests for the presence of human hemoglobin in stool samples from the colon.
The chemical method will yield a positive result if there is any bleeding in the gastrointestinal tract, but it is easily influenced by food or medications and is only for reference.

Reply Date: 2019/12/02

More Info

Understanding stool tests can be quite complex, especially when faced with varying results from different testing methods. In your case, you underwent two types of stool tests: a chemical test and an immunochemical test. The chemical test returned a positive result, indicating the presence of blood in your stool, while the immunochemical test was negative, suggesting no blood was detected by that method.

Why Two Tests?
The reason for conducting both tests is that they utilize different methodologies to detect blood. The chemical test (often referred to as the guaiac test) is more sensitive to a wider range of substances and can sometimes yield false positives due to dietary factors or medications. For example, certain foods like red meat, and even some medications, can lead to a positive result. On the other hand, the immunochemical test is more specific for human hemoglobin, which means it is less likely to be affected by dietary factors and is generally considered more reliable for detecting lower gastrointestinal bleeding.

Interpreting the Results
The discrepancy between the two tests can be confusing. A positive result from the chemical test suggests that there may be bleeding somewhere in your gastrointestinal tract, but it does not specify the source. The negative result from the immunochemical test indicates that, at least at the time of testing, there was no detectable blood from the lower gastrointestinal tract. This inconsistency could mean that the bleeding is intermittent or that the source is higher up in the gastrointestinal tract, such as the stomach or duodenum.

Next Steps
Given the positive chemical test result and the recommendation for further evaluation, it is prudent to follow your doctor's advice and undergo additional testing. This may include a gastroscopy (upper endoscopy) to examine the stomach and possibly the duodenum, as well as a colonoscopy to inspect the colon. These procedures will help identify any potential sources of bleeding, such as ulcers, polyps, or other abnormalities.

Concerning the Diagnosis
Regarding the diagnosis noted on your referral, it is not uncommon for physicians to document potential conditions based on test results, even if the patient does not currently exhibit symptoms. The codes "R019" (abdominal pain) and "K2971" (gastritis with bleeding) may have been included as precautionary measures to ensure that all potential issues are considered during further evaluation. It’s important to communicate with your healthcare provider about your symptoms and concerns, as this will help guide the diagnostic process.

Conclusion
In summary, while the positive chemical test raises concerns about potential gastrointestinal bleeding, the negative immunochemical test provides some reassurance. The next steps should involve further evaluation through endoscopic procedures to clarify the source of the bleeding. It’s also essential to maintain open communication with your healthcare provider regarding your symptoms and any concerns you may have about the diagnosis or the need for further testing. Your current recovery from flu and normalization of bowel movements is a positive sign, but it’s wise to address the findings from your stool tests thoroughly.

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