TYPHOID ANTIBODIES - serum

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Specimen: 5-10 mL blood in plain tube.

Method: Agglutination (Widal) test to detect antibodies to O and H antigens.

Reference Interval: Consult pathologist.

Application: The test is occasionally useful to support the diagnosis of enteric fever (Salmonella typhi, Salmonella paratyphi) if cultures are negative. Investigation of pyrexia of unknown origin. Antibodies to Vi antigen have been used for epidemiological purposes.

Interpretation: Culture is the definitive method for diagnosis of S. typhi or S. paratyphi infection. Serology is of only limited value because false positives and negatives are common. Increased titres are consistent with infection, the carrier state or immunisation. For a patient who has not been immunised, a positive Widal test is one in which there is a four-fold rise in anti-O antibody or a titre of >100 in a single blood sample taken in the first 3 weeks of the illness.

Reference: Sack RB and Sack DA. In: Rose NR et al eds. Manual of Clinical Laboratory Immunology. 4th ed. ASM Press 1992.

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