The SARS-CoV-2 testing landscape is continually changing as additional tests receive an emergency use authorization (EUA) from the FDA. Technology to conduct molecular, antigen, and serology tests is now available and additional technologies are anticipated. The availability of evidence regarding the performance of these different tests as well as guidelines for their best use in different populations is still limited.
Laboratory testing capacity and turnaround time for results is improving locally and statewide. There is, however, limited availability of point-of-care diagnostic tests.
Laboratories Providing COVID-19 PCR Molecular Testing (9-21-20) Reference Guide LA County Department of Health Services (LAC DHS) has created this guide to help organizations identify a laboratory provider that best fits their needs. This document provides an overview of some of the laboratories offering testing to LA County providers and residents.
California Testing Task Force Lab List The Testing Task Force is maintaining a list of labs that have met certain criteria for readiness and can receive samples for RT-PCR COVID testing.
All laboratories (regardless of their location) that test Los Angeles County residents must register with the California Department of Public health (CDPH).
Only tests with emergency use authorizations (EUA) from the FDA should be used for patient care. A wide variety of molecular tests, antigen tests, and SARS-CoV-2 serologic tests now have EUA.
Test accuracy is dependent on many factors including the test technology, specimen collection and handling, pretest clinical probability of disease, community prevalence of disease, and the specific characteristics of the assay. It is particularly important for clinicians to review the EUA for any SARS-CoV-2 test(s) they are using to understand the specific performance characteristics and the instructions for use. All SARS-CoV-2 EUAs are listed on the FDA COVID-19 Emergency Authorization website.
Molecular tests are currently the most accurate tests for diagnosing COVID-19. Molecular tests detect the unique genetic sequence of the SARS-CoV-2 virus by using nucleic acid amplification (NAA) technology such as reverse transcription polymerase chain reaction (RT-PCR) or other amplification methods (e.g. LAMP). RT-PCR is highly sensitive and specific for detecting SARS-CoV-2 virus and is the recommended “gold standard” method for diagnosing current infection. Most molecular tests are moderate or high complexity and must be run in a laboratory, however some are also authorized to be conducted in the point-of-care (POC) setting under a Clinical Laboratory Improvement Amendments (CLIA) Certificate of Waiver.
Not all molecular tests have equivalent performance. Some POC molecular tests have demonstrated lower sensitivity compared with standard laboratory-based RT-PCR tests. The sensitivity of all molecular tests is dependent on the assay, the timing of testing, sampling technique, and sample type. Molecular tests are considered to be very specific.
Laboratory turn-around time (TAT) for PCR test results should be less than 48 hours, however results can be delayed if laboratories are experiencing high volumes. Currently available POC molecular tests results have a TAT ranging from 15-45 minutes.
See FDA list of EUAs for Molecular Tests for more information on the performance and use of specific authorized tests.
Antigen tests detect the presence of SARS-CoV-2 viral surface proteins. The main advantages of antigen tests is that they have a fast turn-around time for results (within 15-30 minutes), they are relatively simple to perform, and they are less expensive than RT-PCR tests. The currently available EUA authorized SARS-CoV-2 antigen tests are all approved as POC tests for settings with a CLIA waiver and they are intended for use on symptomatic persons within 5-12 days of symptom onset (number of days varies by manufacturer).
While antigen tests are considered very specific for the virus, they are less sensitive than RT-PCR.
See FDA’s list of EUAs for Antigen Tests for more information about the performance and use of specific authorized tests
The best use of antigen tests is still be evaluated. While their intended use is in symptomatic persons early in the course of infection, they are currently being deployed and evaluated for use in asymptomatic persons. Antigen tests can augment other testing efforts, especially in settings where RT-PCR testing capacity is limited or testing results are delayed. Rapid antigen tests should add both clinical and infection control value as they can rapidly “rule in” persons with SARS-CoV-2 infection, particularly when the likelihood of infection is high, such as patients with symptoms suggestive of infection, recent close contacts to a known case, or persons that are part of an outbreak setting. Negative antigen tests in these situations should be confirmed by RT-PCR.
There is limited data to guide the use of antigen tests for screening asymptomatic persons. Antigen testing guidelines released by the CDC and CDPH outline scenarios where antigen tests may be considered for screening asymptomatic persons. They recommend using serial screening (repeat antigen testing at set intervals) to alleviate the lower sensitivity of antigen tests.
To learn more, see current antigen testing guidance:
Serology Tests detect waning or past SARS-CoV-2 virus infection indirectly, by measuring the antibody response to the virus. Serology assays should not replace direct viral detection methods for diagnosing an active SARS-CoV-2 infection. At this point in time, until the presence, durability, and duration of immunity is established, serology tests they should not be used to determine immune status. Healthcare providers and systems considering using serologic tests for patient care should adopt strategies to minimize false positive results as outlined in the CDC antibody testing guidance and summarized briefly below.
A list of EUA authorized serology tests plus performance information can be found here.
Use of Serologic Tests
CDC Recommendations for Use of Serologic Tests include:
Non-diagnostic uses of serological tests:
When SARS-CoV-2 serology tests should not be used:
See CDC COVID-19 Antibody Testing in Clinical and Public Health Settings Guidelines, CDPH Serology Indications Guidance, and Infectious Diseases Society of America (IDSA) Guidelines on the Diagnosis of COVID-19: Serologic Testing for more information.
Healthcare providers and systems are encouraged to expand SARS CoV-2 diagnostic testing to more patients with symptoms of COVID-19. Testing asymptomatic persons may be recommended if they are part of an outbreak or case investigation, or if they are staff or residents in a high-risk congregate living setting, or if they are a close contact to a confirmed case.
Healthcare providers and systems should be able to provide their patients with timely access to SARS-CoV-2 diagnostic testing when indicated. Visit Laboratories Providing Diagnostic Testing to identify a laboratory provider that best fits their needs.
If testing resources are insufficient, providers should follow these prioritiesHighest Priority for Testing
Rationale includes, ensuring optimal care options for all hospitalized patients, lessening the risk of nosocomial infections, and detecting and controlling outbreaks in acute- and subacute-care health facilities and high-risk congregate living settings.Testing is Strongly Encouraged
Rationale includes, ensuring that those who are at highest risk of complications are rapidly identified.Recommend Testing assuming sufficient resources
Rationale is to detect new cases to decrease community spread.
Routine testing of asymptomatic persons in the general population is not recommended in the absence of a known exposure.
If such testing is undertaken it is important to emphasize that if they test negative that it only means that the test did not detect the virus at the time the test was taken. A negative result can also happen if the test was taken too early and/or the test missed the infection. A negative test does NOT mean the person can safely ignore physical distancing and mask requirements. Refer the patient to Information about Testing.
Note: if facilities elect to conduct pre-admission or pre-procedure screening of patients for COVID-19, it is important to continue to practice COVID-19 infection prevention precautions on patients testing negative due to the risk of false negatives.