Quality control of loop-mediated isothermal amplification (LAMP) using external control: Detection of SARS-CoV-2 using nasopharyngeal specimens

We evaluated an external control for loop-mediated isothermal amplification (LAMP) for the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using 100 nasopharyngeal specimens (20 positives and 80 negatives). We performed LAMP for the specimens and distilled water. We collected threshold time (Tt) and calculated the difference in Tt values between specimens and distilled water. All specimens showed amplification of the external control. Regarding the Tt values (median, min), no difference was found between the positive specimens (15.9) and the negative specimens (15.8) (p = 0.75). For the difference in Tt values, no difference was found between the positive specimens (1.4) and the negative specimens (1.3) (p = 0.78). No specimens were found with noticeable inhibitory reactions. These results indicate that the external control has the potential to monitor the inhibitory reactions in specimens. Future work will include the evaluation of specimens with inhibitory reactions.