What is guaiac used for in medical testing?

Guaiac is primarily used in medical testing as a reagent in fecal occult blood tests (FOBT). It aids in the detection of blood in stool, which can indicate various health conditions, including colorectal cancer. The guaiac resin reacts with the heme portion of hemoglobin, producing a color change that signifies the presence of blood.

In the context of FOBT test cards, guaiac serves as a coating that interacts with any hemoglobin present in the stool sample applied to the card. When the test is performed, if blood is present, it will react to the guaiac, allowing healthcare providers to diagnose or rule out potential issues related to gastrointestinal bleeding.

The other functions mentioned in the incorrect options do not pertain to guaiac. For example, measuring blood sugar levels relies on different testing methods and reagents. Preservation of samples is generally achieved through other means such as refrigeration or the use of specific preservatives, while analyzing blood gases requires specialized equipment and procedures unrelated to guaiac. Thus, the application of guaiac in the FOBT context makes it a critical component in the early detection of serious health issues.