What is the Widal Test?

About Widal Test: 

• It is a test done for diagnosing typhoid fever.
  • Typhoid fever, also known as enteric fever, is a bacterial infection caused by the bacterium Salmonella Typhi, and it is commonly spread through contaminated food or water. 
  • A person with typhoid fever will experience symptoms like fatigue, high fever, headache, diarrhoea or constipation, abdominal pain, weight loss, and red spots.
  • These symptoms mimic those of malaria, dengue, influenza, and typhus, to name a few, making it difficult to diagnose without proper testing.
• As with other infections, our immune system produces antibodies in the blood against the bacteria, causing enteric fever. 
• The widal test is a serological test that detects antibodies against the bacteria in a patient’s blood sample, indicating whether or not they have been infected with the bacteria. 
• It is used to help diagnose a current or recent infection or to determine if an individual has had a previous typhoid infection.
• It’s a point-of-care test and doesn’t need special skills or infrastructure.
• Developed in the late 1800s by a French physician, it is no longer used in many countries because of its flaws. The World Health Organization (WHO) has said that due to the various factors that can influence the results of a Widal test, it is best not to rely too much on this test.
• Limitations:
  • A single positive Widal test report doesn’t necessarily mean a typhoid infection is present, and a negative report doesn’t confirm the disease’s absence.
  • To diagnose an active infection, clinicians must test at least two serum samples taken at least 7-14 days apart, so that they may detect a change in the concentrations of the antibodies. But getting two samples is rarely feasible and time-consuming.
  • In areas with a high and continuous typhoid burden, certain levels of antibodies against the bacteria may already be present in the blood. Without knowing the baseline cut-off, it isn’t possible to correctly interpret the test.
  • The reagents used in the Widal test to reveal the presence of various antibodies can cross-react with antibodies produced against infections by other bacteria, viruses or parasites, or even in typhoid-vaccinated individuals, leading to false positives.
  • Prior antibiotic therapy can also affect antibody levels and yield a false negative.