The rubella hemagglutination inhibition (hi) test is the most sensitive serologic method available for diagnosis of infection and for determination of immunity status. At present, however, it is not a well-standardized procedure and several modifications are in use. Comparison of results obtained on the same specimens by different laboratories has shown wide variations. The sensitivity and reliability of the technique is decidedly influenced by each of the variables of the test system; these include erythrocytes, antigen, methods employed for removal of non-specific inhibitors and natural agglutinins from test sera, the pH of the diluents and the temperature of incubation. The presence or absence of hi antibody cannot be determined reliably by screening a single low dilution of serum. Commercially available reagents and kits for rubella hi tests vary widely in their reliability. The test should be performed only by experienced persons who understand the principles of the technique and who are aware of the pitfalls and of the importance of using adequate controls in each run.
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