Patients with vaccine-induced immune thrombotic thrombocytopenia (VITT) have been described as having platelet-activating antibodies detectable with PF4-heparin ELISA assays, and possibly with functional assays such as the serotonin release assay. Only a limited number of patients have been described to date, and testing algorithms remain in development. For more information, please refer to the Vaccine-Induced Immune Thrombotic Thrombocytopenia Testing section in the ARUP Consult COVID-19 topic.

Laboratory testing is the only way to distinguish between infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other infections with similar symptoms. Furthermore, laboratory testing is the only way to determine cases of viral coinfection.¹ Patients may be infected with multiple viruses at the same time, so diagnosis of infection with one respiratory virus does not exclude the possibility of infection with another virus.^2,3 The National Institutes of Health (NIH) recommends cotesting to determine proper medical management if multiple viruses (eg, SARS-CoV-2, respiratory syncytial virus (RSV), and influenza A/B) are circulating, such as during flu season.^1,3

Viral testing for SARS-CoV-2 infection may be used for diagnostic purposes (eg, when testing individuals with symptoms consistent with COVID-19), screening purposes (eg, when testing asymptomatic individuals with known or suspected recent exposure to SARS-CoV-2), and surveillance purposes (eg, when testing asymptomatic individuals to detect transmission hot spots or characterize disease trends). Nucleic acid amplification (NAA) testing is the gold standard for detection of SARS-CoV-2 virus.^4,5

Yes. Some multipathogen molecular assays can detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).² Clinicians are advised to confirm which respiratory viruses are detected by an assay before ordering. The U.S. Food and Drug Administration (FDA) maintains a list of COVID-19 assays with Emergency Use Authorization (EUA) that includes respiratory virus panels.

The latest CDC guidance for SARS-CoV-2 testing can be found in the CDC’s Overview of Testing for SARS-CoV-2 (COVID-19).⁴ According to the CDC, viral detection testing (eg, NAA, antigen testing) is recommended for individuals with signs or symptoms consistent with COVID-19.⁴ Testing may also be incorporated as a part of transmission reduction strategies. Diagnostic testing for asymptomatic individuals with known or suspected recent exposure to SARS-CoV-2 may also be advised.⁴

Local and regional health authorities may provide additional guidance for prioritizing patients for COVID-19 testing. Clinicians are also encouraged to consider testing for other causes of respiratory illness, including influenza.

Antibody testing is not currently recommended to diagnose infection or to infer an individual’s immunity to the virus. It may aid in determining the rate of exposure in a given population.

Children of all ages are at risk for COVID-19 infection. Children appear to present with more mild signs and symptoms than adults.⁷ Although severe disease is uncommon, children are still at risk of developing severe illness and complications from COVID-19.

It is unclear whether children are as susceptible to SARS-CoV-2 infection compared with adults. Evidence suggests that, compared with adults, children likely have similar viral loads in their nasopharynges and similar secondary infection and transmission rates,⁷ and that children can spread the virus effectively in households and camp settings.⁸

The CDC is investigating reports of multisystem inflammatory syndrome in children (MIS-C), a serious condition marked by inflammation that may be related to resolved COVID-19 infection.

Clinicians should watch for signs and symptoms, which may include a persistent fever, elevated inflammatory markers, and multiorgan (eg, cardiac, gastrointestinal, renal) involvement.⁷ For more information, refer to the CDC’s case definition for MIS-C.⁹

Nasopharyngeal (NP) specimens are the gold standard for COVID-19 viral detection. Some laboratories may accept alternative specimen types such as saliva, oropharyngeal (OP) swabs, midturbinate swabs, or anterior nares swabs.^5,10 The CDC Specimen Collection Guidelines contain detailed information about EUA-approved specimen types.¹¹ Clinicians are advised to check with their performing laboratory for specific specimen requirements.

Studies, including one performed by researchers at ARUP and University of Utah Health,¹² found that self-collected saliva and NP swabs collected by healthcare providers are equally effective for SARS-CoV-2 detection. Both saliva and NP swabs are superior to anterior nasal swabs. The study, published in the Journal of Clinical Microbiology, represents one of the largest COVID specimen-type comparisons to date.¹² However, saliva specimens are not suitable for all tests that detect SARS-CoV-2.

Detection rates in specimen types vary from patient to patient and may change over the course of the illness.¹³ For example, because of potentially discordant shedding of virus in the upper versus the lower respiratory tract, patients with pneumonia may have negative nasal or OP samples but positive lower airway samples.^14,15

Serum and plasma are the standard specimen types for COVID-19 serology testing. Most commercial assays, including those utilized at ARUP Laboratories, are only validated in these specimen types.¹⁶ Alternate specimen types, such as cerebrospinal fluid (CSF) and cord blood, are inappropriate for use in assays for which they have not been validated. Clinicians are advised to check with their performing laboratory for specific specimen requirements.

The CDC approved the use of capillary fingerstick specimen collection for some point-of-care assays. The CDC Specimen Collection Guidelines¹¹ contain more detailed information about EUA-approved specimen types.

Swab specimens should be collected with NP ultrafine or equivalent swabs. Dacron, polyester-tipped, or any other flocked swabs are acceptable alternatives. Calcium alginate swabs or swabs with wooden shafts are NOT acceptable due to test interference. Viral transport media and universal transport media (VTM/UTM) are the preferred collection systems for swabs. Media types that are equivalent to VTM/UTM are also acceptable.

Saliva specimens are self-collected in ARUP’s saliva collection tubes. This method reduces healthcare providers’ risk of exposure during the collection process. The patient should not eat or drink for 30 minutes prior to providing a saliva sample. Saliva should not surpass the fill line on the tube. Saliva specimens must be collected in the presence of a healthcare provider.

For more information, refer to ARUP’s COVID-19 Specimen Collection Guide.¹¹ For alternative transport media, refer to the FDA’s guidance on specimen collection for SARS-CoV-2 molecular diagnostic testing.¹⁰

COVID-19 diagnostic (nucleic acid amplification) or serologic testing is useful for determining current or past SARS-CoV-2 infection status but is not useful in the evaluation of post-COVID-19 conditions. The CDC provides interim guidance for laboratory testing to evaluate patients with post-COVID-19 conditions.¹⁷ In short, the CDC recommends that laboratory testing should be informed by a detailed evaluation of patient history, physical examination, and clinical findings. Basic laboratory tests (e.g., blood count, liver function, etc.) may be informative.