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

Table 1 Case reports of false positive cryptococcal antigen

Ref.	Age (yr)/gender	Country	Underlying disease (including Immunosupressive disease or drug use)	Sample source/Detection method/Reagent company	Basis of diagnosis	Possible causes	Outcome
Matsumoto et al[24], 2019	58/F	United States	SLE with secondary immune thrombocytopenic purpura	CSF/LA/CALAS® Meridian Bioscience Inc., Cincinnati, Ohio	(1) Reexamination of serum LA suggested negative; (2) Both CSF ink staining and culture results were negative; and (3) Head MRI showed abnormal signals in the left superior frontal cortex, consistent with subacute ischemia; Cardiac hypertrophy suggested Libman-Sack endocarditis. The final diagnosis was "thromboembolic cerebrovascular transient ischemia"	Nonspecific interference with the autoantibodies of SLE circulation in patients	Survived
Augeret al[25], 2019	26/M	United States	None	CSF/LA	Blood and CSF culture identified Df-2 infection	Common antigenic surface components may exist in DF-2
Volozhantsev et al[26], 2020	33/M	United States	Aplastic anemia; after bone marrow transplantation	Serum/LA/ IM Inc, American Microscan	The autopsy confirmed Trichosporon asahiti infection	Similar structures of polysaccharides may exist in Trichosporon asahiti	Died
Zhu et al[27], 2018	29/F	United States	Non-Hodgkin's lymphoma	CSF/LA/CALAS, Meridian Diagnostics, Cincinnati, Ohio, and CRYPTO-LA, International Biological Laboratories, Cranbury, New Jersey	CSF culture indicated Stomatococcus infection	Stomatococcus infection may cross-react with LA	Died
This case 1	53/M	China	None	Serum/LFA/ IMMY Immuno-Mycologics, Norman, Oklahoma, United States	(1) Anticryptococcal treatment failed; and (2) Lung puncture tissue culture suggested aspergillus	Insufficient sample dilution	Survived
Case 2	67/F	China	Bronchial asthma	Serum/LFA/ IMMY Immuno-Mycologics, Norman, Oklahoma, United States	Lung biopsy and left supraclavicular lymph node biopsy indicated lung adenocarcinoma	Insufficient sample dilution	Survived
Case 3	67/M	China	Post-orthotopic liver transplantation	Serum/LFA/ IMMY Immuno-Mycologics, Norman, Oklahoma, United States	(1) The local hospital reexamination of CRAG was negative; and (2) Anti-bacterial therapy was effective	Insufficient sample dilution	Survived

SLE: Systemic lupus erythematosus; CSF: Cerebrospinal fluid; LA: Latex agglutination; MRI: Magnetic resonance imaging; CRAG: Cryptococcal antigen.