I'm NOT ashamed to ask this..... (Re: antibody titer)

This is most likely simple math or what-have-you, but I'm going to ask anyway:

Let's say that a certain criteria list states that the titer has to be > 1:8 for something to be positive. And let's say a question says that the titer is 1:16. Then shouldn't a titer of 1:16 be considered NEGATIVE?

Isn't 1:16 LESS THAN 1:8? (one in sixteen seems less than one in eight).

The criteria says that if it's ABOVE 1:8, it's positive.

The question: "A 33 year-old multipara at 17 weeks' gestation. Indirect Coomb's = + for an antibody that's associated with HDON. The father of the baby is positive for the antigen. The antibody titer = 1:16. Is the fetus at risk for anemia?"

The answer is "Yes". But shouldn't it be NO? since the titer is less than 1:8?


I hate math.

Knicks said:

This is most likely simple math or what-have-you, but I'm going to ask anyway:

Let's say that a certain criteria list states that the titer has to be > 1:8 for something to be positive. And let's say a question says that the titer is 1:16. Then shouldn't a titer of 1:16 be considered NEGATIVE?

Isn't 1:16 LESS THAN 1:8? (one in sixteen seems less than one in eight).

The criteria says that if it's ABOVE 1:8, it's positive.


I hate math.

Click to expand...

You start with 1:1 ratio of the stuff & keep diluting it until you can no longer detect it. So 1:8 is LESS diluted than 1:16 hence something turning positive in 1:16 is STRONGER than turning positive in 1:8

Hope that helps

FutureInternist said:

hence something turning positive in 1:16 is STRONGER than turning positive in 1:8

Click to expand...

..cuz you had to dilute it more, right?

gotchya.

Thanks, man/woman.