Incremental yield of three serial lateral flow lipoarabinomannan assays in the diagnosis of tuberculosis among HIV-positive inpatients at Kiruddu Hospital

Abstract

Background: Lateral flow urine-TB Lipoarabinomannan (LF urine-TB LAM) testing has proven beneficial in diagnosing TB among patients with advanced HIV disease. However, the yield of a single spot test remains suboptimal, and strategies are needed to improve the diagnostic yield. We assessed the incremental yield of three serial LF urine-TB LAM tests in diagnosing TB among hospitalised patients with HIV compared to a single spot LF urine-TB LAM test. Methods: We conducted a cross-sectional study at Kiruddu National Referral Hospital among hospitalised patients with HIV. Consecutive inpatients with HIV aged over 18 years who met WHO criteria for TB screening using LF urine-TB LAM were enrolled. Spot urine samples were tested using LF urine-TB LAM and Xpert® Ultra and sputum for Xpert® whenever available. Participants with negative LF urine-TB LAM on-spot testing underwent further early morning and afternoon urine tests. The incremental yield was calculated as the difference between the proportion of positive LF urine-TB LAM tests from serial testing and positive results from the initial spot test alone. Poisson regression analysis was used to assess the factors associated with positive LF urine-TB LAM. Results: Of 145 participants enrolled, 81 (55.6%) were female, and nearly half were aged 18-35. The median CD4 count was 73 cells/mm3. The yield of LF urine-TB LAM increased from 42.8% (n=62) to 53.8% (n=78) with serial testing (p<0.001). Notably, this was much greater in the probable TB category where the increase in yield of urine-TB LAM from spot to early morning was 27.1% (p<0.001). Blood pressure less than 90 mmHg was significantly associated with positive urine TB LAM (aPR = 1.6, 95% CI: 1.09-2.23, p = 0.014). Non-significant trends were observed with anaemia (PR = 1.58, p = 0.410), urine pH < 7 (aPR = 2.23, p = 0.187), and specific gravity < 1.010 (aPR = 0.69, p = 0.171) and >1.020 (aPR = 0.55, p = 0.231) Conclusion: Serial LF urine-TB LAM testing is a valuable approach for detecting additional TB cases among hospitalised HIV patients, especially those with negative GeneXpert® results, hypotension, and anaemia. Larger studies are recommended to validate these findings.