Validity and reliability of immunochromatographic IgM/IgG rapid tests for COVID‐19 salivary diagnosis

Abstract

Objectives To assess the accuracy of three immunochromatographic rapid tests for salivary detection of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens and the reliability of these tests comparing saliva with plasma samples. Materials and methods Plasma and saliva samples from 62 patients diagnosed with COVID-19 and 20 healthy volunteers were assayed. IgM/IgG antibody against SARS-COV-2 was detected using three immunochromatographic rapid tests and compared with real-time reverse transcription-polymerase chain reaction (qRT-PCR). Results The tests' overall accuracy for detecting anti-SARS-CoV-2 antibodies ranged from 75.6 to 79.3 for saliva and 86.6 to 87.8 for plasma tests. The sensitivity of saliva and plasma tests increased with the severity of coronavirus disease 2019 (COVID-19) signs and symptoms. The chance of a positive plasma test in participants with a positive qRT-PCR test was 2.27 greater than a positive saliva test. Conclusions Although rapid immunochromatographic tests are more accurate using plasma than saliva, which was expected considering its original use, our findings support the use of saliva as a straightforward supplementary method to assess seroconversion in patients with COVID-19, with important sensitivity and sensibility, especially in severe and critical cases.