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* STUCK on this question..... need help
 #487501  
  doctorofusmle - 02/26/10 07:41
 
  Prozone phenomenon... WHAT IS THIS ??

if antibody excess or Antigen excess.... Precipitate will be supoptimal....test will be Falsely -ve

WHYYYYYYYYYYYY???? i am not getting this ...

there are 3 phases in Ag/Ab precipitates
1. Ag excess
2. Equivalence zone
3. Ab excess


We cant detect Diseases in Equivalence Zone.... like Heb B ....

and 1 and 2 Will give is false Negative ...

than where we should run our screening test ...

basically what i am asking is what is Prozone phenomenon....

this is on Kaplan ME page 93 .... even in Kaplan immuno ....


thanks in advance ..... pls help
 
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* Re:STUCK on this question..... need help
#2037202
  sammy10 - 02/26/10 08:35
 
  Prozone phenomenon is when the antigen and antibodies are in equal amount and they bind eachother fully. No antigen or antibody is left for us to detect. Thus the test is false negative. This is what causes the window period  
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* Re:STUCK on this question..... need help
#2037296
  psychmledr - 02/26/10 10:33
 
  doctorofusmle, hope this helps:

The prozone phenomenon is defined as a falsely negative (=incorrectly normal) test due to very high titers (concentration) of either antigen or antibody.

Many laboratory tests rely on antigen-antibody interactions. The prozone phenomenon is said to be present when dilution of a previously negative sample leads to a positive test. High levels of antigen or antibody may prevent the formation of antigen-antibody complexes.

Examples include high levels of syphilis antibodies in HIV patients or high levels of cryptococcal antigen leading to false negative tests in undiluted samples. This phenomenon is also seen in serological tests for Brucellosis.
 
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* Re:STUCK on this question..... need help
#2037370
  doctorofusmle - 02/26/10 12:13
 
  psychmlder

Thanks for the both info .... 2nd is nice but still i am kinda confused bcaz you did not try to pin point those small points ... but still appreciated ...


sammy10 ...

if u go to med essential, the explanation you gave is for window period .... this is what bothering me too ...
this is what they wrote abt; prodrome phenomenon : formation of suboptimal amount of precipitate in antibody excess ....

and beneath this defination, they wrote window period defination, which is what you just gave me .... this is make me confuse ....

now my question is .... window period and prozone phenomenon are SAME thing???
 
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* Re:STUCK on this question..... need help
#2037414
  psychmledr - 02/26/10 13:01
 
  No, they are not.
Window period and equivalence zone are the same thing.
 
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* Re:STUCK on this question..... need help
#2037423
  psychmledr - 02/26/10 13:15
 
  The antigen-antibody precipitin curve is a bell-shaped curve that depicts the titration of ag and ab.

The central part of the bell-curve is the equivalence zone where amount of ag=amount of ab

On the right side of the curve, ag is in excess.
On the left sid of the curve, ab is in excess-this is where the PROZONE phenomenon can occur...where ab is in excess.
It is a rare phenomenon, but when it is supected, the solution will be diluted so that the amount of ab can be balanced.

I tried to place the graph here for you, but I could not.
 
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* Re:STUCK on this question..... need help
#2037444
  tophan - 02/26/10 13:40
 
  we should know :
1-precipitation test are applied for soluble antigen.
2- binding Ab. and Ag. in preciting Rx. are dependent to
a-affinity
B-AVIDITY
C-relative proportion of Ab. and Ag.
the last one is important to form 3 pheomena:
prozone P, equivalent Zone P.,postzone P.

always Ab. and Ag. would be in proportion inorder to make multimolecular lattice(it means it become bigger in size)--->precipitation

always we should know that the reaction and action between Ab. and Ag. are revesible and unstable. the only way you can overcome by making a cross link have them big and bigger. that is happening in equivalent zone.

so if you have F-ve :you might be in these 2 outliar zones:
ifin the pre.--->by diluting you artifitially make that proportion
if in the post---> you repeat the test after a while inorder giving time to body make antibody.

I hope now you can apply this concept to any condition and disease.
GL












--->increase in size until it precipitate
 
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* Re:STUCK on this question..... need help
#2037449
  sammy10 - 02/26/10 13:44
 
  yeah you are right guys. The two phenomena are different.  
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* Re:STUCK on this question..... need help
#2037504
  doctorofusmle - 02/26/10 14:43
 
  psychmledr

Thanks man, really appreciated ...


tophan
MIND BLOWING explanation .... especially the way you divided 3 parts in prozone P, equivalent Zone P.,postzone P..

thanks :)
 
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* Re:STUCK on this question..... need help
#2037506
  doctorofusmle - 02/26/10 14:44
 
  psychmledr

Thanks man, really appreciated ...


tophan
MIND BLOWING explanation .... especially the way you divided 3 parts in prozone P, equivalent Zone P.,postzone P..

thanks :)
 
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* Re:STUCK on this question..... need help
#2037511
  doctorofusmle - 02/26/10 14:46
 
  tophan

I just found this on answer.com and this makes me lil confused not alot ;) ...

The prozone phenomenon is defined as a falsely negative (=incorrectly normal) test due to very high titers (concentration) of either antigen or antibody.


You said Ab... but they are saying Antigen axcess too...

we have to dilute for both ???

and why they are only refering to secondary syphilis .... It can b EBV which cxs atypical antibody too ...?? rite ??
 
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