Template:COVID-19 Testing, Reporting, and Information Management in the Laboratory/Diagnostic testing of COVID-19 and other coronaviruses/Current test methods and their differences

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2.4 Current test methods and their differences

NOTE: Information shown here may rapidly become outdated given how quickly response to pandemic testing can change. A full attempt to keep the content relevant will be made.

2.4.1 Background on the laboratory testing environment

Before continuing, it should be noted that many elements of the prior-mentioned COVID-19 testing guidance have governmental public health laboratories in mind. However, as the scale of the epidemic has grown, the need for commercial laboratories and assay developers to get involved with efforts towards increasing analytical testing throughput—through a more rigorous public-private partnership—has become abundantly clear.[1][2][3][4] Even so, at least in the United States, turnaround times have been slow due to a variety of factors, from lack of in-house laboratory resources to handle high test volumes and a slower-than-expected ramping up of test kit production[1][3][4], to actually getting diagnostic assays that are more rapid (yet still accurate) in their diagnosis, simpler to use, and useable at the point of care.[5][6] The good news is examples of these rapid point-of-care molecular test kits are now becoming available around the globe, including the United States as part of the U.S. Food and Drug Administration's EUA process.

As the demand for expanded diagnostic testing grows in the face of a pandemic, it's important to compare the U.S. laboratory testing environments of public health and large commercial testing labs with those of small, in-office clinical labs. In the U.S., all but research-based laboratory testing of human specimens is regulated under CLIA, including public health laboratories. Of the more than 256,000 non-exempt CLIA-registered labs in the U.S., only 33,212 or 13 percent of them are certified to perform moderate- and high-complexity testing.[7] Your public health labs and commercial diagnostic labs fall into this category, with investments in the personnel, training, certifications, and equipment to conduct those sorts of tests. Contrast this with the small yet numerous physician office laboratories (POLs) and how they operate. As of October 2019, nearly 46 percent of CLIA-certified laboratories in the United States are POLs.[7] Located in an ambulatory or outpatient care setting, these labs test specimens from human patients to assist with the diagnosis, treatment, or monitoring of a patient condition. Testing in the clinical lab generally depends on three common methodologies to meet those goals: comparing the current value of a tested substance to a reference value, examining a specimen with microscopy, and detecting the presence of infection-causing pathogens.[8]

These POL's operate in a different environment than your average public health laboratory or reference lab that receives, processes, and reports on specimens en masse. The POL is typically a smaller operation, performing simple laboratory testing that can produce useful diagnostic data cheaply and rapidly. Rather than performing advanced pathology and molecular diagnostic procedures that require specific equipment and expertise, the POL typically focuses on blood chemistry, urinalysis, and other testing domains that don't require significant resources and provide rapid results. This can be seen in Centers for Medicare and Medicaid Services statistics reported in October 2019 that show nearly 67 percent of POLs in the U.S. are certified to provide CLIA-waived tests[7], "simple tests with a low risk for an incorrect result."[9]

As of the end of April, with 1. all but a handful of the current EUAed molecular in vitro diagnostic COVID-19 test kits being limited to moderate- and high-complexity CLIA labs[10] (the FDA claims that EUAed SARS-CoV-2 tests authorized for "use at the point of care" are considered CLIA-waived tests[11]), and 2. local government entities such as New York City's Department of Health and Mental Hygiene sending reminders to local laboratories that serology testing (as of April 7) is also still considered high-complexity in nature[12] (though the FDA has EUAs for serology tests that are approved for both moderate and complex CLIA labs[10]), a significant majority of clinical laboratories are shut out from assisting with the effort to test the U.S. population for SARS-CoV-2 infection. Given the rapid rate of change at multiple levels of government and society, and wildly varying levels of reliable information being given to the public[13][14], it's important to remember these fundamental differences in laboratories when trying to explain to someone why they are, as of yet, unable to go to their primary care physician and get tested for SARS-CoV-2 in the doctor's office. Should researchers develop and the FDA provide EUAs for more CLIA-waived point-of-care assays, these differences may become less noticeable, and more people will be able to be tested.

2.4.2 PCR-based

As of April 28, the U.S. Food and Drug Administration (FDA) has 42 EAUs for molecular in vitro diagnostic test kits. Forty-one of those 42 test kits use some form of RT-PCR methods, with most using real-time versions of RT-PCR (rRT-PCR). Thirty of those 41 are only authorized to be used in CLIA-certified high-complexity laboratories, with nine being rated for both moderate- and high-complexity. Two RT-PCR kits—Mesa Biotech's Accula SARS-Cov-2 Test and Cepheid's Xpert Xpress SARS-CoV-2 Test—have an additional authorization for point-of-care (POC) use (and thus CLIA-waived use) when used with their authorized POC devices.[10]

Of course, there are many more test kits than those approved in the United States. The Foundation for Innovative New Diagnostics (FIND) is currently "collating an overview of all SARS-CoV-2 tests commercially available or in development for the diagnosis of COVID-19."[15] As of April 28, their site shows more than 180 commercialized manual NAAT tests around the world (most being RT-PCR), with more than 20 in development. AdVeritasDx test and controls database is also useful.[16]

2.4.3 LFA- and LAMP-based

LFAs are currently rare, but due to their advantages of being quick and useable at the point of care, some have suggested that as a format for antigen and antibody (serology) testing, they could positively change the testing landscape.[17][18][19] As of April 28, only three LFA serology tests have received EUAs by the FDA for moderate- and high-complexity CLIA-certified labs. An article by Sheridan in Nature Biotechnology highlights a handful of others developed around the world (see their Table 1).[17] FIND shows more than 120 commercialized rapid diagnostic immunoassay tests around the world, though it's not clear how many of them actually LFAs (from their list, only one is explicitly stated as being LFA).[15] At this point, it's safe to say that LFA are still being developed, and it may be May or June before we start seeing more of them, at least in the United States.[18]

Also of note is the LAMP (and RT-LAMP) method. Abbott's ID NOW COVID-19 test is described by the FDA as using "isothermal nucleic acid amplification technology for the qualitative detection of SARS-CoV-2 viral nucleic acids."[20] This is presumably a loop-mediated isothermal amplification or LAMP test, the only one so far approved by the FDA. Among FIND's list of more than 180 commercialized manual NAAT tests around the world, five of them are explicitly shown to be some form of LAMP test. Multiple preprint papers on medRxiv and bioRxiv suggest that RT-LAMP could provide rapid results for SARS-CoV-2 testing[21][22][23][24], and Abbott is stating its EUAed ID NOW COVID-19 test can be completed within five minutes[25], providing further optimism for rapid point-of-care testing in the near future.

2.4.4 Blood serum

Blood in tubes (9617266704).jpg

Blood serum or serology assays come in three common varieties: LFA, enzyme-linked immunosorbent assay (ELISA), or neutralization assay.[26] As discussed prior, LFAs are intended to be rapid point-of-care tools for qualitatively testing body fluids for patient antibodies or viral antigen. The ELISA is, in contrast, a more lab-bound method which produces results that are qualitative or quantitative. In the context of COVID-19 testing, ELISA tests for the presence of patient antibodies in a given specimen based upon whether or not an interaction is observed with the viral proteins present on the test plate. However, even if antibodies are present, ELISA isn't able to tell a clinician if those antibodies are able to protect against future infection. Neutralization assays are the lengthiest to complete, taking from three upwards to five days.[26] This is largely due to the fact that the assay depends on culturing cells that encourage growth of the target virus. Afterwards, introduced patient antibodies, if present, will fight to prevent viral infection of cells. This process is performed in decreasing concentrations, giving the clinician an opportunity to "visualize and quantify how many antibodies in the patient serum are able to block virus replication."[26] In contrast to ELISA, a neutralization assay is able to determine if a patient's antibodies are actively fighting against the target virus, even after recovering from the infection.

Johns Hopkins' Center for Health Security appears to be tracking serology-based COVID-19 tests that are in development or have been approved in various parts of the globe. However, for the most up-to-date list of serology tests that have received EUAs in the United States, the FDA's EUA list appears to be the best source. As of April 28, the FDA shows eight serology assays approved for diagnostic use in the U.S. Of those eight, three appear to be LFAs and the other five ELISA-based.

A review of Johns Hopkins' tracking list in early April showed more LFA-based tests among those approved in other parts of the world. ScanWell Health's kit appears to be proprietary, but given its claims of rapid results, it's probably LFA. A Singapore-based operation has two tests, one that is advertised as rapid and another as a neutralization test. Of the 22 assays approved for research or surveillance, six appear to be based on ELISA, one is unknown, and the rest are LFA-based assays. Among those still in development, an LFA stands out for integrating CRISPR detection.[27] CRISPR (clustered regularly interspaced short palindromic repeats) represents bacterial and archaeal DNA sequences derived from DNA fragments of previous infection. This genetic material can then be used as an activator of biomarkers when attached RNA "guides" find a match with target viral RNA in patient specimen.[28]

2.4.5 Testing alternatives and challenges

We’ve never faced this before, where clinical labs needed to very quickly be able to ramp up a test so fast.[29]
 
- Jennifer Doudna, Executive Director of the Innovative Genomics Institute, University of California, Berkeley

Though the dismantling and fund-cutting (proposed and real) of government programs designed to protect the populace from pandemics—as well as shortfalls in funding overall[30]—have likely hobbled local, national, and global response to COVID-19[31][32][33][34], it should be recognized that this pandemic may arguably represent a once-in-a-century type of event.[35][36] That said, even the most well-prepared governments would still face challenges in quickly learning about, controlling, and developing therapies for a novel disease agent. Shortages in supplies, workers, funding, and other resources are inevitably caused with a pandemic as people across all types of infrastructure fall ill.[30][37] This requires the additional human elements of adaptability, drive, and shared knowledge to find new and alternative solutions to fighting the challenges inherent to fighting against a novel disease.

See for example a non-peer-reviewed paper published on bioRxiv in early April 2020, where Schmid-Burgk et al. point out that though RT-PCR methods are the most common for currently testing for SARS-CoV-2, "global capacity for testing using these approaches, however, has been limited by a combination of access and supply issues for reagents and instruments." They propose "a novel protocol that would allow for population-scale testing using massively parallel RT-LAMP by employing sample-specific barcodes." They claim that a single heating step, pooled processing, and parallel sequencing with computational analysis would allow for the testing and tacking of "tens of millions of samples." Though the protocol has not been validated with clinical samples, and concerns about sensitivity levels of RT-LAMP (an isothermal nucleic acid amplification technique that allows for RNA amplification) have been raised, the authors' work exemplifies the immediacy and ingenuity going into finding workable solutions to a once-a-century problem.[21]

Another example of ingenuity in the face of difficult circumstances can be found at the University of California, Berkeley. Its Innovative Genomics Institute (IGI) has rapidly repurposed a 2,500-square-foot scientific lab into an automated diagnostic laboratory that can initially process more than 1,000 patient samples per day, with the ability to ramp up to 3,000 per day thanks to robotics and a streamlined workflow. Partnering with dozens of people from Thermo Fisher Scientific, Salesforce, Third Wave Analytics, and Hamilton Corp., the lab is focused on not only turnaround time but also accuracy of results through automation. Their continued success, of course, relies on a steady supply of reagents and related supplies from Thermo Fisher.[29][38]

Others have also expressed concerned about the global supply of reagents necessary to test for SARS-CoV-2. Successful testing using RT-PCR requires two different enzymes: reverse transcriptase, for converting RNA to DNA, and polymerase, for amplifying the converted DNA. These enzymes and other reagent components may be instrument-specific, and at least one component has to be sympathetic to detection of the target virus' RNA. Little of this can be prepared without a proper sequence of the virus in question. Dr. Ronald Leonard, president and medical director of Cytocheck Laboratory and medical director of the Labette Health hospital, has expressed the difficulties associated with reagent manufacturing thusly[39]:

With the instant demand for SARS-CoV-2 testing, the manufacturing process had to start from scratch for the SARS-CoV-2 specific components, and this did cause a lag time before reagents were available. The increased demand coupled with the decision to only allocate reagents to two national laboratories, some state health departments, and to "hot spots" has compounded the difficulty for laboratories like ours to obtain the necessary reagents to perform the testing.

Reports of reagent shortages appeared in March and April from various sources[40][41][42][43], though whether the shortage is a real supply issue or "a consequence of restrictive policies on where and how testing could be completed" is argued by some.[39][42] Others have taken matters into their own hands in regards to reagent component shortages. Noting Irish laboratories' difficulties sourcing lysis buffer (for isolating molecules of interest and keeping them stable), Cork Institute of Technology's Dr. Brigid Lucey worked with several other virologists and microbiologists, as well as pharmaceutical company Eli Lilly, to produce a custom-formulated yet high-quality lysis buffer for not only Irish laboratories but also other countries can take advantage of. "We are happy to share what we found with other countries and it’s important our scientists retain their skills to make this kind of formulation because we may need to do this again in the future if we get other pandemics," she said.[43]

One other challenge lies in the accuracy of serology-based antibody tests, let alone how much they actually tell us about immunity. FierceBiotech's Conor Hale touch upon this in late April[44]:

Compared to molecular tests—which sequence and match the RNA of the novel coronavirus to produce a result—the FDA has described antibody tests that gauge the body’s immune system response as a less-complicated endeavor that could proceed without review, dubbed “regulatory flexibility” by Commissioner Stephen Hahn. This policy shift has led to confusion, with some antibody test developers falsely claiming their tests are FDA-approved or could diagnose COVID-19 at home. Still others have sold outrightly fraudulent tests online.

At least in the U.S., these problems are compounded by company participation in test validation of EUAs being voluntary.[44] As a memorandum from Congress puts it: "FDA is unable to validate the accuracy of antibody tests that are already on the market, and companies are ignoring requests from the Department of Health and Human Services (HHS) to voluntarily submit their tests for validation ... FDA has failed to police the coronavirus serological antibody test market, has taken no public enforcement action against any company, and has not conveyed any clear policy on serological tests..."[45] The entire memorandum is revealing in the challenges of attempting to relax social distancing measures under the pretense of the effectiveness of antibody testing. Entities such as the University of California - San Francisco[46] and the University of California - Berkeley[47] have been emphasizing the importance elements such as sensitivity, specificity, proper training, and the unknowns of the predictive ability of the test. With public confusion growing and expectations increasingly out of line with the science[48], it's more important than ever for leaders across government, healthcare, and the media to continue to not spread misinformation and not make decisions based on poor scientific evidence.

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