A Widal test is used to detect antibodies in the blood that are produced in response to Salmonella typhi and Salmonella paratyphi, the bacteria responsible for typhoid fever. It measures specific antibodies (O and H antigens) to help identify an active or recent infection. Doctors usually recommend this test when symptoms like prolonged fever, headache, abdominal pain, weakness, diarrhea, or loss of appetite suggest the possibility of typhoid fever.

For the Widal test, a small blood sample is taken from a vein, and no fasting is required. The test helps support the diagnosis of typhoid fever, especially in areas where the disease is common. However, it is often interpreted alongside clinical symptoms and other tests like blood culture for more accurate results.