Please explain a titer test to me

[2boyzmama]

And, if you know it, the difference between a titer and an antigen stimulation test.

My understanding is that a titer test will check for existing immunities (either from natural illness or from vaccination). For example, my son had natural chicken pox, however his varicella titer is negative, meaning that he did not acquire immunity from it (expected that he would not, he has an immune deficiency).

My son also had a negative antigen stimulation test result to tetanus. This is different than a titer, correct? I thought that a negative (or low) antigen stimulation test result suggests that he will not respond appropriately to a tetanus vaccine. Am I correct?

His immunologist said that he expected the antigen stimulation test to be negative since my son hasn't been vaccinated...but that sounds like he's talking about a titer test.

Help!

[Dmitrizmom]

Titer will tell you if immunity was developed (and maintained) - measures circulating antibody to a specific antigen.


I'm looking in my immunology books for info on the other.

[ccohenou]

Antigen stimulation testing measures the response of lymphocytes to a specific antigen - ie do they respond and proliferate. I don't think antigen stimulation testing would tell you whether he will respond to a vaccine for an antigen he's never met before, because it takes time for lymphocytes to recognize antigen and mount their response.
Titers measure the level of free immune globulin - antibodies in the plasma.

[2boyzmama]

Originally Posted by ccohenou

Antigen stimulation testing measures the response of lymphocytes to a specific antigen - ie do they respond and proliferate. I don't think antigen stimulation testing would tell you whether he will respond to a vaccine for an antigen he's never met before, because it takes time for lymphocytes to recognize antigen and mount their response.
Titers measure the level of free immune globulin - antibodies in the plasma.

Okay, if this is true, then why run the antigen stimulation test for tetanus on a non-vaccinated child? (the dr knew he wasn't vaccinated, we discussed it at length)

Here's another thing that's confusing me...he has low lymphocytes, we've known that since he was a year old. In the past we have run mitogen tests on him which have all been normal. So the dr explained to me that although his *number* of lymphocytes is low, their *function* is normal, so that's a good thing. The antigen test is different than the mitogen test, right?

I'm still not understanding the difference between a titer and an antigen stimulation test then. It sounds like the results basically tell you the same thing...whether the child's immune system responded properly to a previously introduced antigen (virus, bacteria)? So the varicella titer being negative tells us that he did not acquire immunity from his natural infection. But his tetanus antigen stimulation test being negative tells us nothing at all because he's never been exposed to tetanus before?

[Dmitrizmom]

here's the thing... you can be exposed to tetanus through environmental mechanisms, not develop clinical tetanus, but develop an immune response. Vaccination is not the only route of exposure... current medical science believes vaccination to be the safest route to get that exposure. the negative tetanus antigen stimulation test tells us that he hasn't been exposed to tetanus by any route, vaccination or otherwise.

[Otto]

Originally Posted by Dmitrizmom

here's the thing... you can be exposed to tetanus through environmental mechanisms, not develop clinical tetanus, but develop an immune response.

This is pretty rare in the literature. The only cases I'm aware of suggest intestinal colonization by C. tetani as the route.

[ccohenou]

They're not exactly testing for the same thing. If your lymphocytes could differentiate and proliferate when stimulated, but weren't secreting free Ig into the serum, then you would get a positive AST but negative titer. As to why your doctor is ordering the tests, I don't know; hopefully he would be willing to communicate with you about his reasoning and what he is looking for.