An occult blood test yields a positive result indicated by color change to which color?

An occult blood test yields a positive result indicated by color change to which color?

• A. Red
• B. Green
• C. Blue
• D. Yellow

Answer: (C)

An occult blood test detects the peroxidase activity of hemoglobin. In a guaiac-based test, the guaiac substrate reacts with hydrogen peroxide in the presence of hemoglobin to produce a blue color. This blue color indicates a positive result, meaning occult blood is present. Other colors do not reflect this reaction, so they do not indicate a positive test. Diet and medications can affect results, potentially causing false positives or negatives.

An occult blood test detects the peroxidase activity of hemoglobin. In a guaiac-based test, the guaiac substrate reacts with hydrogen peroxide in the presence of hemoglobin to produce a blue color. This blue color indicates a positive result, meaning occult blood is present. Other colors do not reflect this reaction, so they do not indicate a positive test. Diet and medications can affect results, potentially causing false positives or negatives.