Cold agglutinin titration vs Indirect Coombs for AIHA - USMLE Forums
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Old 09-30-2011
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Question Cold agglutinin titration vs Indirect Coombs for AIHA

Hey all,

I got a question from Kaplan CK QBank : describing a case of Cold Autoimmune Hemolytic Anemia.

The question was : Give the most appropriate test to diagnose this patient's anemia.

Among the options were :
b) Cold agglutinin titration
d) Indirect coombs test


Kaplan's answer was (b) cold agglutinin titration, and they say "answer (d) Indirect coombs is wrong because it looks for circulating antibodies such as testing blood before transfusion, and is not commonly used in evaluating autoimmune hemolytic anemia".

Is that right? I thought Coombs is always used in autoimmune hemolytic anemia?
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Old 09-30-2011
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Default It's the direct Coombs!

You're right, but it said INDIRECT Coombs test, the one to do for AIHA is the DIRECT test. The explanation describes the indirect one, done in pregnant women and prior to transfusions.
Direct Coombs tests for Ab or complement BOUND to red cells and it would be positive in AIHA!
So between those answers, the right one is cold agglutinin titration. If the other one would have been DIRECT Coombs, then I would have said direct Coombs test is the most appropriate next step but agglutinin titration is the most accurate step.
Hope this helped.
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Old 10-01-2011
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Quote:
Originally Posted by dr_mhm View Post
You're right, but it said INDIRECT Coombs test, the one to do for AIHA is the DIRECT test. The explanation describes the indirect one, done in pregnant women and prior to transfusions.
Direct Coombs tests for Ab or complement BOUND to red cells and it would be positive in AIHA!
So between those answers, the right one is cold agglutinin titration. If the other one would have been DIRECT Coombs, then I would have said direct Coombs test is the most appropriate next step but agglutinin titration is the most accurate step.
Hope this helped.
dr_mhm is correct
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Old 10-01-2011
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Quote:
Originally Posted by dr_mhm View Post
You're right, but it said INDIRECT Coombs test, the one to do for AIHA is the DIRECT test. The explanation describes the indirect one, done in pregnant women and prior to transfusions.
Direct Coombs tests for Ab or complement BOUND to red cells and it would be positive in AIHA!
So between those answers, the right one is cold agglutinin titration. If the other one would have been DIRECT Coombs, then I would have said direct Coombs test is the most appropriate next step but agglutinin titration is the most accurate step.
Hope this helped.
Also all individuals have circulating antibodies directed against red blood cells, but their concentrations are often too low to trigger disease (titers under 64 at 4C). In individuals with cold agglutinin disease, these antibodies are in much higher concentrations (titers over 1000 at 4C).
Other major Differentials including Paroxysmal cold hemoglobinuria and drug induced autoimmune hemolytic anemia can have positive coomb;s but titers are less then 164 or or negative in these cases .So titers are more specific in detecting,though they are not necessary for diagnosing and moreover Direct coombs is much easier to perform.
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