What is the correct antibody titer result indicated by the following results: 1:2 1:4 1:8 1:16 1:32 1:64 1:128 with positive reactions?

What is the correct antibody titer result indicated by the following results: 1:2 1:4 1:8 1:16 1:32 1:64 1:128 with positive reactions?

• A. 1:16
• B. 1:32
• C. 1:64
• D. 1:8

Answer: (C)

The main idea is that the antibody titer is defined by the highest serum dilution that still gives a positive reaction. You test a series of twofold dilutions (1:2, 1:4, 1:8, 1:16, 1:32, 1:64, 1:128, etc.), and the endpoint is the last dilution that remains positive. In this set, positive reactions are observed up through the 1:128 dilution. That means the endpoint is 1:128, so the antibody titer should be reported as 1:128. If a provided answer lists 1:64, that would reflect an endpoint at 1:64, but with the dilutions shown, the last positive is at 1:128, making 1:128 the correct titer.

The main idea is that the antibody titer is defined by the highest serum dilution that still gives a positive reaction. You test a series of twofold dilutions (1:2, 1:4, 1:8, 1:16, 1:32, 1:64, 1:128, etc.), and the endpoint is the last dilution that remains positive.

In this set, positive reactions are observed up through the 1:128 dilution. That means the endpoint is 1:128, so the antibody titer should be reported as 1:128. If a provided answer lists 1:64, that would reflect an endpoint at 1:64, but with the dilutions shown, the last positive is at 1:128, making 1:128 the correct titer.