Laboratory Diagnosis of Current, Recent, or Past Infection
A definitive diagnosis of a current COVID-19 infection can be made by identifying viral genetic material (RNA) in a person’s respiratory system using molecular techniques.3,7 These techniques usually involve nucleic acid amplification tests (NAAT) based on real-time reverse transcription-polymerase chain reaction (real-time RT-PCR).3 Rapid testing for viral antigens has been recently developed; however, these tests are not as sensitive as molecular techniques for detecting active infections.8 Regardless of the method employed for COVID-19, testing should have received emergency use authorization (EUA) from the FDA.
The CDC recommends using a viral (nucleic acid or antigen) test to diagnose acute infection.7 Antibody testing (see Recent or Past Infection) is not recommended by the CDC for acute infections.7
For initial diagnostic testing for SARS-CoV-2, the CDC recommends collecting and testing an upper respiratory tract specimen. Nasal, nasopharyngeal, or oropharyngeal specimens are acceptable when collected according to CDC guidelines. Suboptimal collection techniques increase the chance of obtaining false-negative test results.9 Accordingly, the CDC provides guidance on the use of washes/aspirates and swabs, which specimens should be collected by a healthcare professional, and when supervised on-site or home self-collection is appropriate.9 Less invasive sampling methods include mid-turbinate or anterior nares specimens as the source for viral nucleic acid testing.9
Testing lower respiratory tract specimens is also an option, either from sputum from a noninduced productive cough, or from a lower respiratory tract aspirate or bronchoalveolar lavage.9
A positive test result for SARS-CoV-2 (COVID-19) in a symptomatic patient indicates that viral RNA was detected; the patient is infected with the virus and is presumed to be contagious. For asymptomatic individuals, detection of viral RNA does not necessarily mean that viable infectious virus is present. Prolonged detection of RNA without direct correlation to viral culture has been reported.5 However, because there are no symptoms, it is not possible to gauge where these patients are in the course of the infection. Thus, asymptomatic patients who test positive for SARS-CoV-2 RNA should also be considered contagious (see Sidebar).7
A “not detected” (negative) test result means that SARS- CoV-2 RNA was not present in the specimen above the limit of detection. A negative result does not rule out the possibility of COVID-19, however, and should not be used as the sole basis for treatment or patient management decisions.
An “inconclusive” result means not all of the viral RNA targets were detected. The sample may have viral concentrations near the limit of detection of the test, or other factors may have influenced the result, and an additional sample collection may be requested.