The Widal test is a complex serological procedure that involves the mixing of the bacteria that is responsible for the typhoid fever, also known as enteric fever, and the human blood that has certain antibodies taken from a patient suffering from typhoid. The most important point in this test is to interpret the test results carefully according to the previous history of the typhoid fever and the history of typhoid vaccination of the patient.
According to MyHealthyFeeling, the Widal test procedure can be done in two ways: slide agglutination and tube agglutination. The tube agglutination procedure is more accurate than the slide agglutination procedure, but the latter is faster. The procedure involves the following steps.
- Preparing a blood plate whose background should be black
- Adding one drop of serum
- Adding the antigens which include the H, AH and BH
- Mixing the antigens and the serum
- Rotating the sample for about one minute
- Interpreting the results which may be either positive reactive or negative non-reactive
The antibodies normally develop towards the end of the first week while the titres rise in the course of the second, third and the forth week. After this period, the titres gradually decrease and this is why a Widal test procedure may give negative results if performed within the first days of the first week.