Abstract Body

Thailand has one of the highest TB/HIV burdens globally. The 2020 Thai national HIV treatment guidelines recommend rapid TB urine LF-LAM testing as an additional TB diagnostic test to assist with TB diagnosis among people living with HIV (PLHIV) who present with 1) signs and symptoms of active TB, 2) critical illness (respiration rate >30 breaths/minute, body temperature >39°C, heart rate >120 beats/minute), or 3) CD4 cell count <200 cells/mm3 for in-patient and <100 cell/mm3 for out-patient with or without signs and symptoms of active TB. This study assesses the yield of the Alere Determine™ TB LF-LAM test in diagnosing active TB in PLHIV and factors associated with positivity.

National TB/HIV data from PLHIV at least 15 years old who met eligibility criteria for urine LF-LAM testing at 17 hospitals in 8 provinces from October 2020 to August 2021 were analyzed. Definite TB diagnosis is defined as having single sputum Xpert-MTB/RIF and TB culture positivity or either of these two diagnoses independently. Probable TB is defined as a clinical diagnosis by a doctor, abnormal chest X-ray, and being treated with TB regimens. We examined urine LF-LAM test accuracy, sensitivity, and specificity in diagnosing definite and probable TB and performed random effects logistic regression modeling to identify factors associated with urine LF-LAM positivity.

Of 488 PLHIV with urine LF-LAM test results, 179 (37%) were TB cases including 45 (25%) definite TB and 134 (75%) probable TB. The median age was 39 years, 118 (65%) were in-patients, and 131 (73%) were male. Table 1 shows test performance in assisting in the diagnosis of definite and probable TB cases. Overall LF-LAM test accuracy, sensitivity and specificity were 79%, 60%, and 90%, respectively and higher among CD4 <200 cells/mm3 at 81%, 66%, and 92%, respectively. The Positive Predictive Value was 83% among CD4 <200 cells/mm3 and 41% among CD4 >200 cells/mm3. Multivariable logistic regression revealed LF-LAM positivity among PLHIV with TB disease associated with CD4 <100 cells/mm3 (aOR: 3.47, 95% CI 1.22 – 9.86) and clinical weight loss (aOR: 3.57, 95% CI 1.83 – 6.96) after adjusting for hospital type.

The LF-LAM urine testing can assist in diagnosing active TB in PLHIV with CD4 <200 cells/mm3 in Thailand. Specificity was high, but the LF-LAM should be used in combination with other TB diagnostics for the most accurate diagnosis. The benefits of using LF-LAM in improving patient outcomes should be further studied.