Test Principle

Test Principle

This product was developed in order to detect the urease activity of H. pylori in stomach biopsy specimens. Urease in the biopsy specimen catalyzes hydrolysis of urea present in the test device.

This reaction produces ammonia which leads to an increase in pH of the medium. Increased pH turns the color of the indicator ring from yellow to reddish/pinkish color. The formula of the reaction is as follows:

Urea + Water → Carbon dioxide + Ammonia

Interpretation of the Results

Positive Results: The result is positive if the outer ring’s color changes from yellow to reddish/pinkish. The severity of the infection can be guessed depending of the speed of the reaction and the intensity of red color. The inner circle remains yellow and serves as a reference to color change.

Negative Result: If the outer circle remains yellow and there is no change to red then the result is negative. Wait for 60  minutes to report negative result. 

Sensitivity: Urease enzyme (Merck, Kat No: 1.16493.0010, Lot: HC270495) was diluted in deionized water so that the final concentration of the enzyme is 1 U/ml. 5 µl of enzyme solution (5 mU of urease) was applied to the device. Color change began within a minute and was completed to bright red circle within 5 minutes. All biopsy tests for detection of H. pylori are subject to false negative results because of sampling errors. Colonization of the microorganism can be patchy so the biopsy specimen taken may be from an area without infection. Additionally, proton pump inhibitors may alter the colonization of the microorganism and antral biopsies may not be correct. In order to increase the sensitivity you should consider taking biopsies from different parts of the stomach.

Specificity: The test method relies on the reaction of urease enzyme and urea. The product of this reaction increases the pH of the medium, increased pH changes the color of indicator pad from yellow to red. This reaction is catalyzed only by urease enzyme. Studies made with other urease producing microorganisms have shown that H. pylori has a unique urease which has higher activity and has higher affinity to its substrate. Thus other microorganisms which may be present in the biopsy specimen will not be able to yield enough product within the test period to give a color change (positive result). This makes this test specific for H. pylori.