Abstract
BackgroundThe accurate diagnosis of TB in HIV-infected patients, particularly with advanced immunosuppression, is difficult. Recent studies indicate that a lipoarabinomannan (LAM) assay (Clearview-TB®-ELISA) may have some utility for the diagnosis of TB in HIV-infected patients; however, the precise subgroup that may benefit from this technology requires clarification. The utility of LAM in sputum samples has, hitherto, not been evaluated.MethodsLAM was measured in sputum and urine samples obtained from 500 consecutively recruited ambulant patients, with suspected TB, from 2 primary care clinics in South Africa. Culture positivity for M. tuberculosis was used as the reference standard for TB diagnosis.ResultsOf 440 evaluable patients 120/387 (31%) were HIV-infected. Urine-LAM positivity was associated with HIV positivity (p = 0.007) and test sensitivity, although low, was significantly higher in HIV-infected compared to uninfected patients (21% versus 6%; p<0.001), and also in HIV-infected participants with a CD4 <200 versus >200 cells/mm3 (37% versus 0%; p = 0.003). Urine-LAM remained highly specific in all 3 subgroups (95%–100%). 25% of smear-negative but culture-positive HIV-infected patients with a CD4 <200 cells/mm3 were positive for urine-LAM. Sputum-LAM had good sensitivity (86%) but poor specificity (15%) likely due to test cross-reactivity with several mouth-residing organisms including actinomycetes and nocardia species.ConclusionsThese preliminary data indicate that in a high burden primary care setting the diagnostic usefulness of urine-LAM is limited, as a rule-in test, to a specific patient subgroup i.e. smear-negative HIV-infected TB patients with a CD4 count <200 cells/mm3, who would otherwise have required further investigation. However, even in this group sensitivity was modest. Future and adequately powered studies in a primary care setting should now specifically target patients with suspected TB who have advanced HIV infection.
Highlights
Tuberculosis (TB) kills almost two million people annually [1] and is out of control in Sub-Saharan Africa where up to 80% of TB patients may be co-infected with HIV [2]
Smear microscopy had a sensitivity of 65%, 49% and 37% in unselected TB patients, in HIV co-infected patients, and in those
In this study we show that in unselected HIV-infected or uninfected ambulant TB suspects LAM has little clinical utility in a high burden primary care setting
Summary
Tuberculosis (TB) kills almost two million people annually [1] and is out of control in Sub-Saharan Africa where up to 80% of TB patients may be co-infected with HIV [2]. Delayed diagnosis facilitates disease transmission, increases healthcare costs, increases mortality, and causes greater lung damage resulting in chronic disability [4]. These drawbacks are exacerbated in HIV-infected patients, where the diagnostic ‘gap’ is the widest - smear-positivity in this sub-group is as low as 20% [5], and the clinical and the radiological features are often atypical [6]. Mycobacterial culture results are only available after several weeks, if at all, in resource-poor settings [7] Newer technologies such as the T cell assays are not useful as rule-in tests for the diagnosis of active TB in adults [8], and molecular assays [7] are not widely available in high burden countries. The utility of LAM in sputum samples has, hitherto, not been evaluated
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