The Sensitivity and Specificity of Loop-Mediated Isothermal Amplification (LAMP) Assay for Tuberculosis Diagnosis in Adults with Chronic Cough in Malawi

Abstract

BackgroundCurrent tuberculosis diagnostics lack sensitivity, and are expensive. Highly accurate, rapid and cheaper diagnostic tests are required for point of care use in low resource settings with high HIV prevalence.ObjectiveTo investigate the sensitivity and specificity, and cost of loop-mediated isothermal amplification (LAMP) assay for tuberculosis diagnosis in adults with chronic cough compared to Xpert® MTB/RIF, fluorescence smear microscopy.MethodsBetween October 2013 and March 2014, consecutive adults at a primary care clinic were screened for cough, offered HIV testing and assessed for tuberculosis using LAMP, Xpert® MTB/RIF and fluorescence smear microscopy. Sensitivity and specificity (with culture as reference standard), and costs were estimated.ResultsOf 273 adults recruited, 44.3% (121/273) were HIV-positive and 19.4% (53/273) had bacteriogically confirmed tuberculosis. The sensitivity of LAMP compared to culture was 65.0% (95% CI: 48.3% to 79.4%) with 100% (95% CI: 98.0% to 100%) specificity. The sensitivity of Xpert® MTB/RIF (77.5%, 95% CI: 61.5% to 89.2%) was similar to that of LAMP, p = 0.132. The sensitivity of concentrated fluorescence smear microscopy with routine double reading (87.5%, 95% CI: 73.2% to 95.8%) was higher than that of LAMP, p = 0.020. All three tests had high specificity. The lowest cost per test of LAMP was at batch size of 14 samples (US$ 9.98); this was lower than Xpert® MTB/RIF (US$ 13.38) but higher than fluorescence smear microscopy (US$ 0.65).ConclusionThe sensitivity of LAMP was similar to Xpert® MTB/RIF but lower than fluorescence smear microscopy; all three tests had high specificity. These findings support the Malawi policy that recommends a combination of fluorescence smear microscopy and Xpert® MTB/RIF prioritised for people living with HIV, already found to be smear-negative, or being considered for retreatment of tuberculosis.

Validating the Loop Mediated Isothermal Amplification (LAMP) technique to detect tuberculosis in a Sri Lankan laboratory setting

“…According to Keeler et al a rapid test requiring less infrastructure facilities with a sensitivity and specificity of 85% and 97% can potentially avert 24% of world deaths due to TB [7]. Although we have not achieved such a high specificity with the LAMP assay in the current study under the tested conditions in local settings, and that it is low compared to other studies, the assay has room for improvement [2,8,9]. For instance, when the reaction mixtures of the MOTT samples, after the LAMP assays, were run in 1% agarose gel (Figure 2), the reaction mixtures of the 5 false positives, showed the presence of some LAMP amplicons, rather than primer dimers, indicating a possibility of a cross contamination during the experi-mentation.…”

Diagnostic test accuracy of loop-mediated isothermal amplification assay for Mycobacterium tuberculosis: systematic review and meta-analysis

“…Although we generally understand the advantage of Xpert MTB/RIF over LAMP, many peripheral laboratories in high TB endemic area with limited infrastructures and medical resources cannot afford Xpert MTB/RIF44. LAMP might replace Xpert MTB/RIF in low-income peripheral area where multi-drug resistant TB is not prevalent, though clinicians should carefully consider the result of sputum smear and epidemiology, especially concerning drug resistance, in the area545. Currently, neither LAMP nor Xpert is the ideal tool for peripheral setting.…”

Establishment of an accurate and fast detection method using molecular beacons in loop-mediated isothermal amplification assay

“…These characteristics provide results in a fast, efficient, and cost-effective method that theoretically should amplify target sequences with higher specificity than PCR. Since its introduction, LAMP has seen wide interdisciplinary application, for example in detecting microorganisms (e.g., bacteria23, fungi4, and viruses56) diagnosing genetic diseases7, and even early sex determination8.…”