Validation of clinic-based cryptococcal antigen lateral flow assay screening in HIV-infected adults in South Africa

Drain, P. K., Hong, T., Krows, M., Govere, S., Thulare, H., Wallis, C. L., Gosnell, B. I., Moosa, M. Y., Bassett, I. V. and Celum, C.

Since rapid cryptococcal antigen lateral flow assays (CrAg LFA) may expedite treatment of HIV-associated cryptococcal infections, we sought to validate clinic-based CrAg LFA testing. Among newly-diagnosed HIV-infected adults in South Africa, a trained nurse performed clinic-based testing of urine, fingerprick capillary and venous whole blood with rapid CrAg LFA (Immy Diagnostics, Norman, USA). We performed matched laboratory-based serum cryptococcal antigen testing with an enzyme immunoassay (EIA). We assessed diagnostic accuracy using EIA as the gold-standard, and performed additional validation testing on serum and among hospitalized adults with cryptococcal meningitis. Among 5,618 participants enrolled, 1,296 were HIV-infected and screened for cryptococcal antigenemia. Overall CrAg prevalence by serum EIA was 3.6% (95% CI 2.0-6.0%) for adults with CD4 < 200 cells/mm(3), and 5.7% (95% CI 2.8-10.2%) for adults with CD4 < 100 cells/mm(3). Using expanded screening guidelines (CD4 < 200 cells/mm(3)), CrAg LFA testing of venous whole blood, fingerprick capillary blood, and urine had diagnostic sensitivities of 46% (95% CI 19-75%), 38% (95% CI 14-68%), and 54% (95% CI 25-81%), and specificities of 97%, 97%, and 86%, respectively. When tested on serum samples, CrAg LFA had sensitivity of 93% (95% CI 66-100%) and specificity of 100% (95% CI 88-100%). All venous and fingerprick whole blood CrAg LFA tests were positive among 30 hospitalized adults with cryptococcal meningitis. Two independent readers had strong agreement for all LFA results (p < 0.0001). When performed at the point-of-care by trained nurses, CrAg LFA testing was feasible, had the highest accuracy on serum specimens, and may accelerate treatment of HIV-associated cryptococcal infections.

April 12, 2019
Year of publication
Resource types
Journal and research articles
HIV-positive adults, HIV-associated cryptococcal disease, cryptococcal antigen (CRAG), newly diagnosed

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