Chlorine test turns pink after 2 months, is it false negative for HP?

Ask
Hello doctor! I have congestive gastritis, my chlorine test is yellow, but after 2 months I take it out and check the results, it turns pink again. So the doctor asked me, is the chlorine test turning pink after 2 months, is it false negative for HP? Looking forward to your answer, thank you doctor!
Nguyen Van Huy (1996)
Answer
Hello, doctor would like to answer the question: "Is the chlorine test pink after 2 months, is it false negative for HP? ” as follows:
Chlorine test is a test to assess HP infection status, Chlorine test is a type of invasive test, also known as Urease rapid test, detecting HP based on the following principles. HP that exists in the stomach will secrete a lot of ureasse. This yeast is the catalyst for the breakdown of urea into ammonia and carbon dioxide. People use urea - indol to detect, if HP is present, the solution will change from yellow to pink. This method is easy to implement, gives fast results, high sensitivity and specificity in general. However, the disadvantage is that it takes a large enough amount of bacteria to change the color of the urea-indol solution. In addition, the Chlorine test can only detect HP in the active form, leading to false negatives in many cases. Some other bacteria also present in the gastrointestinal tract can secrete urease enzyme such as HP causing false positive.
To avoid false results, patients need to stop taking ACE inhibitors, acid reducers for at least 2 weeks. And stop Bismuth, antibiotics at least 4 weeks before doing the chlorine test.
My results after 2 months of changing color to pink, it is difficult to say exactly because when the outside environment is affected for a long time, it will change the properties of the test, can you check the HP test again through the breath? Endoscopy should be performed to assess the status of HP infection.
You can go to the nearest medical facility or the Hospital of Vinmec Health System for more detailed examination and advice by doctors. Best regards!

Answered by Master, Doctor Ta Que Phuong - Gastroenterologist - Endoscopy - Department of General Internal Medicine, Vinmec Times City International Hospital