Medical Laboratory Scientist (MLS) ASCP Practice Exam

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What is the likely result of the prozone effect when performing a screening titer?

  1. false positive

  2. false negative

  3. true positive

  4. true negative

The correct answer is: false negative

The prozone effect occurs in serological testing where the concentration of antibodies in a sample is so high that it interferes with the formation of the antigen-antibody complexes. This interference can lead to underestimated or non-detectable levels of antibodies during the testing process, resulting in a diminished reaction signal. In the context of a screening titer, if the prozone effect is present, the test may yield a false negative result. This situation arises because the excessive concentration of antibodies prevents the formation of the immune complexes needed for proper detection. Therefore, despite the actual presence of antibodies at a level that would typically indicate a positive result, the test fails to recognize it due to the overly saturated environment caused by the high antibody concentration. Recognizing the prozone effect is crucial for accurately interpreting serological tests, particularly in clinical settings where distinguishing between the presence and absence of an antibody is pivotal for diagnosis. It’s essential for laboratory professionals to be aware of this phenomenon so they can take appropriate steps, such as diluting samples, to avoid misinterpretation of the test results.