POINT OF CARE DIAGNOSTICS
Point of care diagnosis in epidemics is very essential and can be achieved by the use of rapid analysis which can be conducted at ease outside laboratory or near patient in order to facilitate prompt diagnosis, monitoring, management and quick medical decision at early stage of disease development (Vashist, 2017). It is highly needed at the time of epidemics and pandemic such as SARS-CoV and SARS-CoV-2.
Molecular detection of both SARS-CoV and COVID-19 was known to be their recommended means of diagnosis (WHO, 2020). The fact that NAAT require expertise, and is expensive, complex and not easily obtainable at environments outside laboratories, other devises to aid diagnosis that are easy to use are currently recommended at point of care to detect antigens or antibodies or both (WHO, 2020; Ying et al., 2020). Rapid diagnostic test (RDT) is used to detect viral antigens present in the clinical sample if they are in sufficient concentration to bind with the specific antibody against the virus that are fixed on paper and detectable visually within 30 minutes, they are best used in acute stages when the viruses are actively replicating (WHO, 2020). It has been experienced from the antigen based RDTs for respiratory viruses such as influenza and ASRS-CoV that have variable sensitivities and could lead to missed diagnoses (Bruning et al., 2017; Wang et al., 2018), hence further studies are required to understand their accuracy in COVID-19 cases so that if any of the antigen detection strip demonstrate adequate performance they can be used as triage for individuals that have likelihood to harbour COVID-19 (WHO, 2020).
Being that RT-PCR is the gold standard for viral diagnosis and NAAT is globally recommended method for detection of SARS-CoVs, detection of antibodies to COVID-19 become a supplementary option even if a combined IgG/IgM device is to be used. This can be supported with the fact that about 86% of the RT-PCR positive samples have been found to be positive for SARS-CoV-2 IgG/IgM test kit with 91% specificity as demonstrated by Ying et al. (2020).
RDTs that detect the presence of COVID-19 antibodies in the blood are readily available (Cheng et al., 2020). In some infected individuals that are confirmed positive by RT-PCR, there was reported weak or absent antibody responses till after a week or more (Li et al., 2020), which indicate that antibody testing are more reliable at later stage of the disease (Zhao et al., 2020; Okba et al., 2020). For point of care diagnosis, there is limitation for such tests as a result of delayed outcome, but can be useful epidemiological vaccines research and risk assessments (Cheng et al., 2020; WHO, 2020),
At point of care, neither immunoassay nor RT-PCR are ideally reliable, however the later is better in terms of accuracy and speed of development but complex and delays results; the former is less accurate and usually takes long time to develop but easier to use, with results within 20-60 minutes. Immunoassays usually detect antibodies to pathogens from samples and must unavoidably be contended with the variable human polyclonal antibody response that take time to characterize (Sheridan, 2020), efforts are therefore needed to produce more reliable devices.