The Widal test has significant limitations in its specificity, sensitivity and reliability. The test results change with the course of infection.
A false-negative Widal test is more likely in the initial stages of infection or seen in cases where antibody responses in the body are diminished by early microbial treatment or in cases of typhoid relapse. Severe hypoproteinemia can cause decreased titres of antibodies against O and H antigens leading to false-negative results.
A False positive Widal test is seen in cases of the previous infection of typhoid or previous vaccination against typhoid. Widal test shows cross-reactivity with other species of Salmonella bacteria. False-positive results are also seen in cases of Acute Falciparum Malaria (especially in children), Rheumatoid Arthritis, Nephrotic syndrome, Chronic liver disease with low globulin levels.
Widal test needs a reference baseline titres from a healthy local population and this differs from time to time and place to place making it difficult to have a standard cutoff level.