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.