How is the titer determined in an antibody dilution test?

How is the titer determined in an antibody dilution test?

• A. By the highest dilution of serum giving a negative reaction
• B. By the highest dilution of serum giving a positive reaction
• C. By the amount of serum in the last tube
• D. By visual inspection of the color change

Answer: (B)

In an antibody dilution test, the titer represents the strength or concentration of antibodies present in the serum. This is determined by identifying the highest dilution of the serum that still produces a positive reaction. When conducting the test, a series of dilutions of the serum are prepared and mixed with a known antigen. The reactions at each dilution are then observed. The positive reaction indicates that antibodies are present in sufficient quantity to interact with the antigen. As dilutions increase, the concentration of antibodies decreases; therefore, the goal is to find the highest dilution at which a positive reaction is still detectable. This dilution reflects the maximum capacity of the serum to produce a detectable immune response, thus indicating the titer. In contrast, identifying the highest dilution that gives a negative reaction would not provide meaningful information about the antibody concentration, as it focuses on the point at which antibodies are no longer detectable, rather than their highest functional concentration. The other options, such as measuring the amount of serum in the final tube or relying solely on visual inspection of color change, do not accurately reflect the systematic method required to determine the titer in a rigorous and quantifiable way.

In an antibody dilution test, the titer represents the strength or concentration of antibodies present in the serum. This is determined by identifying the highest dilution of the serum that still produces a positive reaction. When conducting the test, a series of dilutions of the serum are prepared and mixed with a known antigen. The reactions at each dilution are then observed.

The positive reaction indicates that antibodies are present in sufficient quantity to interact with the antigen. As dilutions increase, the concentration of antibodies decreases; therefore, the goal is to find the highest dilution at which a positive reaction is still detectable. This dilution reflects the maximum capacity of the serum to produce a detectable immune response, thus indicating the titer.

In contrast, identifying the highest dilution that gives a negative reaction would not provide meaningful information about the antibody concentration, as it focuses on the point at which antibodies are no longer detectable, rather than their highest functional concentration. The other options, such as measuring the amount of serum in the final tube or relying solely on visual inspection of color change, do not accurately reflect the systematic method required to determine the titer in a rigorous and quantifiable way.