I am asking this question because it has been found that patient who were later confirmed positive for COVID-19 infection were initially declared negative. Similarly, patient who, after declared negative and cured, returned a positive test.
Does it depend on the type of sample or the viral load of SARS-CoV-2?
This paper should help answer your question.
Wenling Wang, PhD; Yanli Xu, MD; Ruqin Gao, MD; et al. Detection of SARS-CoV-2 in Different Types of Clinical Specimens. JAMA 2020 (in press)
The reality is that the sensitivity of the test depends on the sampling technique and stage of the infection (i.e. viral shedding).
Broncho alveolar lavage will have the highest yield taking this sample requires bronchoscopy which exposes healthcare professionals to significant aerosolisation.
RIsk stratification is about pre- and post-test probability. If the pre-test probability is high the post test probability will remain high despite a negative poorly sensitive test.
While bronchoalveolar lavage (BAL) is the best sample in acute phase of COVID-19, it is the most invasive and risky for the sampler. Most of sites taking samples for SARS-CoV-19 have been using nasopharyngeal or oropharyngeal swabs for diagnosis using RT-PCR based testing and diagnosis of COVID-19.
i think nasopharyngeal and oropharyngeal swabs is sufficient for diagnosing covid-19
@ Muhammad Ameen
Most of the countries often prefer, a nasopharyngeal swab as a standard initial test for RT-PCR for SARS-CoV-2. Some hospitals, including ours, take both nasopharyngeal as well as oropharyngeal swabs for this purpose as it increases the diagnostic yield for diagnosis of COVID-19.
dear nasopharyngeal swabs give us good diagnostic results and it is difficult to take oropharyngeal swabs
Those who had had the swabbing done for COVID-19 diagnosis know that nasopharangeal swabbing is an unpleasant experience compared to other type of sampling but the gold standard.
Dear Muhammad Yousuf, I believe that currently, the best way to diagnose SARS-CoV-2 infection immediately and unerringly is the use of dogs. Properly trained dogs can detect infection with their nose and are infallible. Since last August, many airports (Dubai, Abu Dhabi, Helsinki, etc.) have been using dogs to identify people with COVID 19.
See:
https://www.researchgate.net/post/Is_it_possible_to_make_an_artificial_nose_to_detect_SARS-CoV-2_infection