This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Widal test is a type of 
Select and explain. 
A. Slide agglutination test, B. Tube agglutination test, C. CFT, D. Ring precipitation test
B: Tube agglutination test
Answer: B: Tube agglutination test 
Explanation: Tube dilution agglutination test (Widal test): Serum agglutinins rise sharply during the second and third weeks of S serotype Typhi infection. The Widal test to detect these antibodies against the O and H antigens has been in use for decades. At least two serum specimens, obtained at intervals of 7-10 days, are needed to prove a rise in antibody titer. Serial dilutions of unknown sera are tested against antigens from representative salmonellae. The interpretive criteria when single serum specimens are tested vary, but a titer against the O antigen of greater than 1:320 and against the H antigen of greater than 1:640 is considered positive.Ref: Jawetz Medical Microbiology; Chapter15 Enteric Gram-Negative Rods (Enterobacteriaceae); Page no: 241