Weil-Felix reaction is a serological test for detecting Rickettsial antibody in serum of patient using heterophile antigen. This is a non specific agglutination reaction.
This test is very useful for diagnosis in case of epidemic typhus.
Both Sensitivity and specificity of weil-felix test is low, but its predictive value can be increased by testing both acute and convalescent phase samples and observing rise in antibody titre.
Weil-felix test has low sensitivity, i.e. its gives high percentage of false negative results. This is common in case of Scrub Typhus.
It also shows low specificity, i.e. false positive results are obtained in other diseases such as leptospirosis, and relapsing fever (diseases which require differentiating from rickettsial infections), in Proteus infections, brucellosis and acute febrile illness.
