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False-positive reactions in the latex agglutination test for Cryptococcus neoformans antigen
J S Heelan1, L Corpus, N Kessimian
1Department of Pathology, Memorial Hospital of Rhode Island, Pawtucket 02860.
Abstract:
The latex agglutination test for Cryptococcus neoformans antigen is a simple and rapid procedure for the diagnosis of cryptococcal meningitis. Although the test is sensitive, care must be taken to prevent contamination of the sample, which may result in false-positive reactions. It was discovered in our laboratory that immersion of a platinum wire inoculating loop into a sample of cerebrospinal fluid prior to testing introduced interfering substances leading to nonspecific agglutination. After further studies, it was determined that trace amounts of surface condensation (syneresis fluid) from agar, either added to the cerebrospinal fluid or adhering to the loop, were the probable source of contamination. It is suggested that the latex agglutination test for C. neoformans antigen be performed prior to culture or on a separate sample.
Insights
Contamination of cerebrospinal fluid samples with agar syneresis fluid can cause false positives in the latex agglutination test for Cryptococcus neoformans antigen. Performing the test before culture or on a separate sample is recommended to ensure accurate diagnosis of cryptococcal meningitis.
Area of Science:
- * Clinical microbiology
- * Diagnostic immunology
Background:
- * The latex agglutination test is a rapid diagnostic tool for cryptococcal meningitis.
- * False-positive results can occur due to sample contamination.
- * Identifying sources of contamination is crucial for accurate diagnosis.
Purpose of the Study:
- * To investigate the cause of nonspecific agglutination in the latex agglutination test for Cryptococcus neoformans antigen.
- * To identify interfering substances introduced during sample handling.
- * To recommend procedural modifications for improved test accuracy.
Main Methods:
- * Laboratory investigation of false-positive latex agglutination test results.
- * Analysis of cerebrospinal fluid samples and platinum wire inoculating loops.
- * Identification of contaminants using agar syneresis fluid.
Main Results:
- * Trace amounts of agar syneresis fluid were identified as a source of contamination.
- * Syneresis fluid, present on inoculating loops or in cerebrospinal fluid, caused nonspecific agglutination.
- * Contamination led to false-positive reactions in the latex agglutination test.
Conclusions:
- * Agar syneresis fluid interferes with the latex agglutination test for Cryptococcus neoformans antigen.
- * Careful sample handling is necessary to prevent contamination.
- * Performing the latex agglutination test before culture or on a separate sample is advised to ensure diagnostic accuracy.