False positive detection of serum cryptococcal antigens due to insufficient sample dilution: A case series

At present, with the development of technology, the detection of cryptococcal antigen (CRAG) plays an increasingly important role in the diagnosis of cryptococcosis. However, the three major CRAG detection technologies, latex agglutination test (LA), lateral flow assay (LFA) and Enzyme-linked Immunosorbent Assay, have certain limitations. Although these techniques do not often lead to false-positive results, once this result occurs in a particular group of patients (such as human immunodeficiency virus patients), it might lead to severe consequences.

Case summary: In the three cases we reported, we found that insufficient dilution of the samples may lead to false-positive results in the detection of cryptococcal capsule antigen, which has never been reported before.

Conclusion: Therefore, once the test results are inconsistent with the clinical symptoms, it is necessary to reexamine the samples carefully. Especially for LFA and LA, the samples can be fully diluted or segmented diluted to avoid false-positive results. It is certain that in the diagnosis, fluid and tissue culture should also be improved, combined with imaging, ink staining, and other methods to improve the accuracy of the diagnosis further.