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

Table 2 Possible causes of false positive results in three cryptococcal antigen detection techniques

Detection method	LA	LFA	ELISA
Sample	Cerebrospinal fluid/Serum	Cerebrospinal fluid/Serum/Plasma /Whole blood	Cerebrospinal fluid/Serum
Possible causes of false positive	Serum of rheumatoid factor, agarose dehydration, hydroxyethyl starch, and containing Fe3+/dL > 200 mg was present, Circular slides are not properly washed, the inactivation of Streptomyces protease in the kit and some nonspecific reactions in patients with HIV infection occur	LFA has antigenic cross-reaction with aspergillus which may lead to false positive results1; Sample dilution is insufficient2	Samples are Infected with other microbial infections, such as Trichosporon1; Reagents and samples to be tested are contaminated2

¹Lateral flow assay (LFA) should not be used as a screening test for the general population, but only should be performed when clinical evidence suggests the possibility of cryptococcosis.

²LFA may also have potential interference factors, including samples pretreated with 2-mercaptoethanol or those containing vaginal ointment, caffeine, ascorbic acid, itraconazole, amphotericin B, acetaminophen or acetylsalicylic acid. However, the above factors have not been systematically evaluated.

LA: Latex agglutination; LFA: Lateral flow assay; ELISA: Enzyme linked immunosorbent assay; HIV: Human immunodeficiency virus.