Serial dilution in Widal test helps to determine the titer of antibodies in the patient's serum by observing the agglutination reaction with specific antigens. By diluting the serum sample in a stepwise manner, the titer at which agglutination occurs can be determined, providing valuable information about the presence and concentration of antibodies against Salmonella typhi and Paratyphi antigens in the blood.
The blood test for typhoid is called the Widal test. It detects antibodies in the blood against the Salmonella typhi bacteria, which causes typhoid fever.
Serial dilution in serology is used to determine the concentration of an antibody or antigen in a sample by making a series of dilutions with a known dilution factor. This allows for the creation of a standard curve to quantify the concentration of the target molecule. Serial dilution helps ensure that the concentration of the sample falls within the detectable range of the assay.
Serial dilution of an agar plate allows for the quantification of bacterial colonies by providing a range of colony counts within the plate, making it easier to count without overcrowding. It also helps to isolate individual colonies for further analysis or microbiological testing. Additionally, serial dilution can help determine the original concentration of bacteria in a sample by calculating the dilution factor.
In a Widal test, "H" refers to the flagella antigen of Salmonella typhi while "O" refers to the somatic antigen of the bacteria. The presence of antibodies against these antigens indicates a recent or current infection with Salmonella typhi, the bacterium that causes typhoid fever.
Serial dilution is usually 1/10 dilution. Therefore after a series of dilutions, you have a logarithmic curve of concentration (log10). Basically, if diluting 1/10 and starting off with 1 molar solution, first dilution = 0.1M, 2nd = 0.01M, 3rd = 0.001M. If making a 0.001M solution involved weighing out 0.005g of a salt for example, the error in making this solution out would be very large in comparison to weighing out 5g (1M) and diluting it 3 times by serial dilution. The benefit of it is mainly accuracy.
That is a good question! The answer is simple. You do step by step dilution of the serum with probably normal (isotonic) saline solution and test the same for Widal test. This is how you do quantitative test for many other tests also.
What is false positive in widal test
The main difference between the Widal slide test antigen and the Widal tube test antigen lies in the method of reaction visualization. In the Widal slide test, the reaction is observed on a glass slide under a microscope, whereas in the Widal tube test, the reaction is seen in small test tubes. Both tests detect antibodies against specific Salmonella antigens, but differ in their setup and visual interpretation.
I mean widal test result positive after treatment
Isolated Widal test reading does not have much clinical significance. Rising titre of Widal test done one week apart, in a febrile patient, indicates typhoid fever. You can have such rising titre of Widal test in healthy patient, after dose of typhoid vaccine.
1:80 titre is significant for determination of widal positive.
widal test
To a certain extent yes.The post antibiotics Widal Test will have Low titers of agglutinins.Hence the test may be reported as False Negative.
The blood test for typhoid is called the Widal test. It detects antibodies in the blood against the Salmonella typhi bacteria, which causes typhoid fever.
manual test of widal method
widal test.
Widal test is negative in incubatory carrier. Widal test is always positive in chronic carrier.