Which type of agglutinins are being measured in the Widal test?

The Widal test is specifically designed to measure the presence of typhoid agglutinins, which include antibodies against the O and H antigens of Salmonella typhi, the bacterium responsible for typhoid fever. In this test, patients' serum is mixed with a suspension of killed Salmonella bacteria, and the agglutination reaction indicates the presence of these antibodies.

The test aims to detect the antibodies produced by the immune system in response to the infection, making it an important diagnostic tool for typhoid fever. A rise in the titre of these agglutinins suggests an active infection or previous exposure to the bacteria.

Understanding the correct choice in this context hinges on recognizing that the Widal test is uniquely utilized for identifying typhoid agglutinins, differentiating it from tests assessing other antibodies, such as rheumatoid factor or anti-nuclear antibodies, which are associated with other disease processes and conditions.