Diagnostic accuracy of HIV Viral Load as a marker for Cryptococcal Antigenemia screening at a tertiary hospital in Uganda

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Abstract Background: Cryptococcal Meningitis (CM), is the second leading cause of HIV-related mortality in Uganda after TB. A CD4 cell count triggered CRAG screening algorithm and pre-emptive therapy is the mainstay of prevention of CM. The recent absolution of routine CD4 monitoring for stable patients on Highly Active Antiretroviral Therapy (HAART) has shifted this trigger to suspected virological failure.Objective: To assess the performance of Viral Load (VL) as a marker for CRAG screening among patients on HAART at an HIV clinic in Mulago National Referral HospitalMethods: This was a cross sectional diagnostic study conducted at the Baylor Uganda Centre of Excellence HIV clinic in Mulago National Referral hospital. Records of 798 HIV positive patients aged 10 years and above, on HAART for at least 6month, with at least one viral load and a corresponding serum CRAG done between January 2017 and December 2018 were extracted from the Electronic Medical Records. The test under evaluation was a VL cut-off of greater or equal to 1000cp/ml (suspected treatment failure) and the Gold standard was Serum CRAG Lateral Flow Assay (LFA). Sensitivity, specificity, positive predictive value, negative predictive value, Likelihood ratio positive, likelihood ratio negative and the Area under the Receiver Operating Characteristic (ROC) curve were then determined using 2x2 contingency tables and ROC curve analysis. Results: Prevalence of CRAG using the gold standard was 0.6% (95%CI: 0.2-1.5). The sensitivity and specificity of VL≥1000cp/ml as a marker for CRAG were 20% (95%CI: 2.1-74.4) and 99.4% (95%CI: 98.4-99.8) respectively. The Area under the ROC curve was 0.56 (95%CI: 0.29-0.82). The likelihood ratio positive and negative were 1.0. The optimal VL cut-off was VL≥49cp/ml with a sensitivity of 60% and specificity of 53%. Conclusion: In populations with low CRAG prevalence, treatment failure (VL≥1000cp/ml) is not a good marker for CRAG screening. A more conservative cut-off of 49cp/ml may be considered were resources allow.

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