Impact of introduction of TB LAM in the TB testing algorithm at Levy Mwanawasa University Teaching Hospital on case detection and notifications

Abstract

Abstract   Introduction TB-LAM tests were introduced in the TB program in Zambia in 2019, to aid in diagnosis of TB. We carried out a study to determine the impact that TB lipoarabinomannan (LAM) test has had on case identification and notification at a tertiary hospital in a city with a high prevalence of HIV. We also compared sensitivity, specificity, positive predictive value and negative predictive of TB LAM tests and X-pert MTB RIF test in HIV positive and HIV negative patients.   Method Retrospective analysis of the TB laboratory as well as the TB notification registers to determine the number of TB cases identified by TB LAM and Xpert MTB-RIF. We identified patients who had both TB LAM and X-pert MTB RIF tests to determine sensitivity, specificity, positive and negative predictive values of TB LAM and Xpert MTB RIF, using TB notification and commencement of anti-tuberculosis treatment as the gold standard for comparison.     Results Between January 2019 and June 2022, there were a total number of 2353 notified cases of Tuberculosis. A total of 511 cases of Tuberculosis were identified on the basis of positive TB LAM. This accounted for 59% of all bacteriologically confirmed cases of TB. The sensitivity and specificity of TB LAM in diagnosis of TB in the study population was 55.8% and 91.4% respectively. Positive and Negative predictive values for TB LAM were 84.5% and 69.6% respectively. The sensitivity and specificity of Xpert MTB RIF in diagnosis of TB in the study population was 29.2% and 98.2% respectively. Positive and Negative predictive values for Xpert MTB RIF were 93.5% and 60.4% respectively. Positivity yield was higher for TB LAM as compared to Xpert MTB RIF (19% versus 9% in 2019; 36% versus 10% in 2020 and 38% versus 10% in 2021). Conclusion TB LAM identified 59% of all bacteriologically confirmed cases of tuberculosis at Levy Mwanawasa University Teaching Hospital. Contrary to what has been found in other studies, the sensitivity of TB LAM was much higher than that of Xpert MTB RIF. In addition, the sensitivity of TB LAM was higher in HIV negative as compared to HIV positive, which is contrary to what has been established in similar studies.