Preferred Specimen(s) 3ml serum
Instructions Separate serum from cells as soon as possible
Transport Container No additive (red-top) tube
Transport Temperature Refrigerated 48 hours
Reject Criteria
- Received frozen;
- Room temperature
Methodology Agglutination on slide
Clinical Significance The Widal test is a presumptive serological test for Enteric fever or Undulant fever that may be caused by Salmonella infections (S. typhi, S. paratyphi A & B). The most important causative factor in India is S. typhi. The antibodies are tested against two types of antigens, the protein H (flagellar) and the polysaccharide O (somatic) antigen. The H antigen is a protein and more antigenic and hence gives higher antibody titers. The H antigen is however relatively nonspecific due to due to shared antigens amongst entero-bacteriaceae. The O polysaccharide antigen gives lower titers and is more specific. A twofold rise in titer is diagnostic of typhoid fever. A single reading of titer more than 240 is also considered as diagnostic.