The Validity and Applicability of Loop-Mediated Isothermal Amplification (LAMP) in the Diagnosis of Malaria in the Philippines

Abstract

Background: While microscopy has remained to be the gold standard in the diagnosis of malaria in epidemiological studies, a number of reports demonstrated that it may have drawbacks in detecting low-level parasitemia and in distinguishing morphological characteristics of some malaria species. Therefore, it becomes necessary to develop alternative species-specific diagnostic tool to replace microscopy.

Objective: This study determined the validity (sensitivity, specificity, positive and negative predictive values) and applicability (inter-reader variability, inter-reader agreement, agreement with microscopy) of Loop-Mediated Isothermal Amplification (LAMP) in the diagnosis of Plasmodium falciparum and Plasmodium vivax in the Philippines.

Methodology: Blood samples from 61 febrile patients from Puerto Princesa City, Palawan were collected for microscopy, DNA extraction, and LAMP analysis. Nucleotide sequences of the 18S rRNA genes were utilized as basis for determining LAMP primer sets. LAMP reaction was performed using the Loopamp DNA amplification kit while the presence of amplified gene products was detected through UV fluorescence.

Results: LAMP Pf showed 100% sensitivity, 94.1% specificity and 95.1% (k = 0.84) agreement with microscopy. The positive predictive value (PPV) and negative predictive value (NPV) are 76.9% and 100%, respectively. LAMP Pv showed 90% sensitivity, 100% specificity, and 98.4% (k = 0.94) agreement with microscopy. The PPV and NPV are 100% and 98.1%, respectively. In the visualization of LAMP, inter-reader variability was absent (%Level I and II Error = 0), and a perfect agreement between observers was observed (k = 1).

Conclusion: Due to its comparable validity and excellent applicability, the LAMP technique described in this study can be an alternative to microscopy in the diagnosis of P. falciparum and P. vivax in clinical laboratories where the disease is endemic.

Key words: malaria, LAMP, microscopy