ifference-in-antibody-titer-between-serum-a-and-serum-b-and-what-does-this-imply

Question

You test two patient sera in parallel with twofold serial dilutions starting at 1:20. Serum A is positive through 1:640 but negative at 1:1280. Serum B is positive through 1:160 but negative at 1:320. What is the fold difference in antibody titer between Serum A and Serum B and what does this imply?

Accepted Answer

Serum A has a 4-fold higher titer (1:640 vs 1:160), implying a stronger antibody response in Serum A.

Answer

Fold differences cannot be calculated from endpoint titers produced by serial dilutions; only ELISA absorbance values permit fold-change interpretation.

Answer

Serum A has a 2-fold higher titer and therefore indistinguishable clinically from Serum B because twofold differences are within assay variability.

Answer

Serum B actually has the higher titer because lower denominators indicate stronger antibody concentration; therefore B is two times higher than A.