From the Guidelines
Urine Tuberculosis (TB) Lipoarabinomannan (LAM) test is a rapid diagnostic test that detects lipoarabinomannan (LAM) in urine samples, particularly useful for diagnosing TB in HIV-positive individuals with advanced disease and low CD4 counts. This test is recommended for use in hospitalized HIV-positive adults, adolescents, and children with signs and symptoms of TB, as it provides rapid results within 25 minutes and is non-invasive, using urine samples 1. The test involves applying a few drops of urine to a test strip and reading the results after 25 minutes, with a positive result appearing as a visible line on the strip.
Key advantages of Urine TB LAM include:
- Rapid results (within 25 minutes)
- Non-invasive (uses urine samples)
- Can detect TB in patients who may have difficulty producing sputum
- Useful in patients with both pulmonary and extrapulmonary TB The test works by detecting LAM, which is released from metabolically active or degenerating mycobacteria, and in HIV-positive individuals with weakened immune systems, there's often a higher bacterial load and more LAM excretion in urine, making the test more sensitive in this population 1.
Some commercial assays, such as the lateral flow urine LAM assay, have a pre-specified threshold for detecting TB positivity, which is used at initial presentation, and it must be specified if this threshold is also used for treatment monitoring purposes 1. While Urine TB LAM is a valuable tool, it should be used in conjunction with other diagnostic methods for TB, as it has limitations in sensitivity, especially in HIV-negative individuals or those with higher CD4 counts.
In terms of study design guidance for evaluating TB treatment monitoring tests, including Urine TB LAM, it is essential to include people who have received a diagnosis of TB and are already undergoing treatment, and to collect key demographic and clinical characteristics that may be relevant to the biomarker(s) under investigation, such as HIV status, baseline drug resistance profile, and history of TB disease 1.
From the Research
Urine Tuberculosis (TB) Lipoarabinomannan (LAM) Test
- The Urine TB LAM test is a diagnostic tool used to detect tuberculosis in patients, particularly those with HIV co-infection or advanced immunosuppression 2, 3, 4, 5, 6.
- Lipoarabinomannan (LAM) is a lipopolysaccharide found in the cell wall of Mycobacterium tuberculosis, which can be detected in urine samples 2, 3, 4, 6.
- The test is particularly useful for diagnosing TB in patients who are unable to produce sputum or have difficulty providing sputum samples, such as those with HIV-induced immunosuppression or children 3, 4, 6.
Test Characteristics
- The sensitivity of the Urine TB LAM test ranges from 13% to 93%, while specificity ranges from 87% to 99% 3.
- The test has improved sensitivity in HIV-TB co-infection, particularly in patients with advanced immunosuppression 3, 4, 5.
- The test can be used as a rule-in test for TB in patients with advanced HIV-induced immunosuppression, allowing for early initiation of antituberculous treatment 4, 5.
Clinical Applications
- The Urine TB LAM test can be used as a point-of-care diagnostic tool for TB, particularly in resource-limited settings 2, 6.
- The test can be used in conjunction with other diagnostic modalities, such as smear microscopy and chest radiography, to improve diagnostic accuracy 4.
- The test has the potential to facilitate global TB control by enabling rapid and accurate diagnosis of TB in adult and pediatric patients, regardless of HIV status or site of infection 6.