Current Testing Options for COVID-19
By Yan H. Lemeshev, M.D.
In late 2019, a viral epidemic broke out in Wuhan, China. This newly isolated coronavirus caused a severe acute respiratory syndrome, which was designated SARS-CoV-2, as it was in the same subgenus of beta coronavirus as SARS-CoV (the etiology of another deadly viral outbreak in China in 2003). The disease associated with SARS-CoV-2 is COVID-19, for coronavirus disease and the year it was identified, 2019.
Coronaviruses, named for the crown-like spikes on the viral surface, have been known for years as one of the causes of the common cold. SARS-CoV-2 has a highly variable presentation with most infected patients exhibiting virtually no or only mild symptoms. Of those who are symptomatic most present with fever, fatigue and dry cough and less commonly with anorexia, myalgias, dyspnea, anosmia and dysgeusia. A small percentage present with gastrointestinal symptoms including nausea, vomiting and diarrhea.
Severe disease occurs in a substantial minority of patients. The overall mortality rate has been variably reported from <1% to between 2-3%, though age, underlying comorbidities and several other factors appear to significantly affect this number. Underlying comorbidities also impact those who progress to having a more severe course and include obesity, cardiovascular disease, diabetes, hypertension, chronic lung disease and cancer.
There are three main strategies currently being pursued for diagnosing SARS-CoV-2: Molecular detection, serologic identification of IgM and IgG antibodies and viral antigen detection.
This is the primary means of viral identification in the acute setting, and typically involves using a swab to obtain a sample from the nasopharynx or oropharynx of a suspected COVID-19 patient. Polymerase chain reaction (PCR) is the general term for a class of nucleic acid amplification tests, in which commercially available oligonucleotide primers and probes are used to detect regions of the SARS-CoV-2 nucleocapsid N1 & N2 gene.
There are various types of PCR, but in general, a positive result indicates the presence of viral RNA, and in a patient with symptoms consistent with COVID-19, is confirmatory of the disease. While a negative result indicates the absence of identifiable viral RNA, factors such as appropriate sampling, sample dilution in transport media and variability of viral particle number can influence the outcome of the test. Numerous manufacturers have been granted emergency use authorization (EUA) for this type of test by the FDA. Manufacturers have produced a wide variety of platforms for this testing methodology from point-of-care devices such as the Abbott ID NOW, which tests individual patients one at a time, to high throughput platforms such as Hologic’s Panther Fusion system, which can test many hundreds of patients per day. This testing methodology can be more expensive to perform and produces results varying from <30 minutes to several hours depending on the manufacturer.
Serologic Antibody Detection
Detection of serum antibodies for SARS-CoV-2 is another option in evaluation of patients for the disease and is currently available via two main methods: Individual test kits qualitatively identifying the presence of IgM and IgG and quantitative evaluation of those antibodies on high throughput immunoanalyzers.
The presence of serum antibodies indicates exposure to a disease and has been studied since the late 1800s. Typically, IgM is the first antibody produced by the body to fight the infection with other Ig classes following it. This should not be the primary method of evaluating patients for COVID-19, as there is typically a several day lag (or window) after infection during which time this test will be negative. The presence of IgM alone or in conjunction with IgG, indicates current/recent infection and IgG in isolation indicates remote disease. Unfortunately, unlike molecular detection of the presence of viral RNA, the detection of serum antibodies says nothing of the patient’s current infectivity with the virus. Additionally, issues with cross-reactivity to other coronaviruses hamper the specificity of these tests.
Manufacturers such as Cellex currently offer qualitative test kits for IgM and IgG detection, while Ortho Clinical Diagnosis offers a total serum antibody test on their Vitros analyzer.
Based on current data, the World Health Organization (WHO) does not recommend the use of antibody-detecting rapid diagnostic tests for patient care but encourages the continuation of work to establish their usefulness in disease surveillance and epidemiologic research.
Viral Antigen Detection
Viral antigen detection uses fluid from a nasal swab sample mixed with reagent, which is then introduced onto a specific window in the test kit. This fluid potentially containing the virus moves across the strip mixing with labeled antibodies. If the virus is present, a visible line appears on the strip in an area designed to catch the labeled antigen-antibody complex and another line appears indicating the test is working properly via a control substance or antibody.
These test kits are typically inexpensive and allow for quick detection of the virus but suffer from all the issues common to kit tests including low throughput. However, this method does have the potential to be used as a screening tool, and because of its low cost and rapid results, would be useful in a variety of situations that require rapid triaging of patients.
Sona Nanotech is an example of a manufacturer that is currently developing this test methodology.
With the limited data now available, WHO does not currently recommend the use of antigen-detecting rapid diagnostic tests for patient care, although research into their performance and potential diagnostic utility is highly encouraged.
PROPATH’S TESTING SOLUTIONS
After extensively researching and evaluating the various options, ProPath has identified molecular and serology tests with strong performance characteristics, and a reliable pipeline of materials, to ensure the availability of quality testing to our clients. As a result, we have partnered with Hologic for molecular identification of SARS-CoV-2 RNA utilizing their Panther system and found this testing platform to provide excellent sensitivity and specificity for viral detection. We feel this combination of tests provides the most reliable answer to the question of whether the patient currently has or has previously had infection with SARS-CoV-2. Molecular testing is currently available to our clients, while serologic testing will be available in late-May, 2020.
THE OBLIGATORY CAVEATS
As is the case when testing for any infectious organism via any methodology, false positives and false negatives are possible, and any clinical decisions should be primarily driven by the clinical scenario regardless of the testing methodology performed or results obtained.
The state of affairs with the COVID-19 pandemic are rapidly evolving, and the information presented in this document is accurate as of late April 2020. Government regulations change regularly, and new manufacturers of various testing methods are reported on an almost daily basis.
According to the FDA, any test that receives EUA for testing via any methodology is required to be performed in a CLIA accredited laboratory approved for high complexity testing unless otherwise explicitly specified. Examples of exceptions include the Abbott ID NOW and Cepheid, which currently only require moderate complexity testing capabilities. Pre-EUA tests, even though many of them are actually very simple to perform, are still classified as high complexity until the EUA review is complete and specifically defined otherwise. None of the current tests on the market in the United States are FDA cleared or approved, and the EUA is only good for the duration of the declared emergency. No advertising or promotional descriptive printed matter relating to the use of any of the authorized tests may represent or suggest that the test is safe or effective for the detection of SARS-CoV-2.
About the author
Board-certified – Anatomic and Clinical Pathology by the American Board of Pathology
Fellowship – Surgical Pathology, University of Texas Southwestern Medical Center, Dallas, TX
Residency – Pathology, University of Texas Health Science Center, San Antonio, TX
Medical School – University of Texas Health Science Center, San Antonio, TX
Dr. Lemeshev is also the Medical Director of Laboratory at Plano Surgical Hospital.
ProPath is a physician-owned medical practice and laboratory offering expert anatomic pathology, esoteric testing, and full-service clinical pathology. Our team of board-certified pathologists have subspecialty training and expertise in virtually every aspect of anatomic pathology. Our team also includes Ph.D. scientists with expertise in Cytogenetics, Molecular Diagnostics, and Flow Cytometry.
With a focus on patient safety, ProPath has invested in today’s technological advances, including proprietary systems to provide accurate and timely processing, tracking, and delivery of results to our clients and patients.
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Dan T. Benscoter, D.O.
Medical Director, Kindred Hospital Arlington, Kindred Hospital Fort Worth Southwest, Kindred Hospital Mansfield, and Weatherford Regional Medical Center
W. Frederick Bierbaum, M.D.
Medical Director, Texas Health Harris Methodist Hospital Southwest Fort Worth, and USMD Hospital at Fort Worth
Carrie Chenault, M.D.
ProPath Medical Director, Director of Flow Cytometry
Medical Director, Pine Creek Diagnostic Imaging Center, and Pine Creek Medical Center Frozen Lab
Rosemary E. Detweiler, M.D.
Medical Director, Texas Health Harris Methodist Hospital Southwest Fort Worth and Texas Health Hospital Clearfork
Michael Y. L. Hew, M.D.
Medical Director, Medical City
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Isabel C. Hill, M.D.
Medical Director, Baylor Scott & White Medical Center at Sunnyvale
Scott E. Kornman, M.D.
Medical Director, Baylor Scott and White Surgical Hospital and Wilson N. Jones Regional Hospital.
Donna J. Lager, M.D.
Director, Renal Pathology
Medical Director, Texas Digestive Consultants
Yan H. Lemeshev, M.D.
Director, Women’s Health
Medical Director, Plano Surgical Hospital
Craig E. Litz, M.D.
Medical Director, Texas Health Surgery Center Dallas, North Central Surgical Center, and Texas Scottish Rite Hospital
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Medical Director, John Peter Smith Hospital
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Medical Director, Texas Health Harris Methodist HEB Hospital
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Medical Director, Medical City
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Horace C. Wu, M.D.
Medical Director, Texas Health Harris Methodist Hospital Southlake.
Lauren Xu, M.D.
Medical Director, Weatherford Regional Medical Center