Evaluation of a cryptococcal antigen lateral flow assay test for rapid detection of cryptococcal infection in HIV-negative patients in Ibadan, Nigeria

Abstract

Background: A number of studies have been conducted in Nigeria on the prevalence of cryptococcal infections mostly on HIV-infected patients using culture, India ink and/or latex agglutination tests. These tests are either laborious, time-consuming and expensive or have low sensitivity, thus limiting their use. Cryptococcal antigen lateral flow assays (LFA) were introduced in the last decade as rapid user-friendly tests for diagnosis. In this study, we sought to determine the diagnostic accuracy of an LFA kit for the detection of cryptococcal antigen in the serum of HIV-negative patients with or without cerebrovascular accident (CVA) or stroke in University College Hospital, Ibadan, Nigeria.
Methodology: The diagnostic accuracy of Dynamiker CrAg LFA was tested against BiosynexR CryptoPS on serum samples of 100 HIV-negative patients with and without stroke. Samples were tested and results interpreted in accordance with the manufacturer’s instructions. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and positive and negative likelihood ratios of the Dynamiker CrAg LFA were calculated by comparing with the BiosynexR CryptoPS as ‘gold standard’.
Results: Overall, a total of 98 valid patient sample results were analysed; 17 samples (17.3%) were positive with Dynamiker CrAg LFA cryptococcal antigen and 16 samples (16.3%) were positive with BiosynexR CryptoPS. The sensitivity, specificity, PPV and NPV of Dynamiker CrAg LFA compared to the BiosynexR CryptoPS were 100%, 98.8%, 94.1% and 100% respectively, while the positive and negative likelihood ratios were 82 and 0 respectively.
Conclusion: In comparison to the BiosynexR CryptoPS, the Dynamiker CrAg LFA is a highly sensitive and specific test for the detection of cryptococcal antigen in serum. The test kit should be considered as a screening device for cryptococcal infection both in outreach and clinical settings, especially in antiretroviral therapy (ART) centres.

Keywords: Cryptococcus; evaluation; lateral flow assay; HIV-negative; stroke