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COVID-19 Test Sensitivity is Unclear. How Accurate is COVID-19 Test?


April 21, 2020

Harsha Moole, M.D., MBBS


COVID-19 Test Sensitivity is Unclear. How Accurate is COVID-19 Test?

Context: This blog post is regarding health care providers encountering potential COVID-19 patients at hospitals / urgent cares / clinics. A Physician Scientist’s perspective.


Learn about COVID-19 transmission on a separate blog post: How is COVID-19 Transmitted? What is the Right Mask for COVID-19? A Physician-Scientist’s Perspective.

Learn about KN95 vs. N95 Masks on a separate blog post: KN95 vs. N95 Masks – It Is Time to Use Common Sense


Summary:

  • The sensitivity of COVID-19 test in the US is unclear1. Firsthand experiences of many physicians (including myself) taking care of COVID-19 patients suggest that there are a significant number of patients that initially test negative for COVID-19, but later test positive on a repeat COVID-19 test after a few days.
  • This is a concerning finding, suggesting a possibility of high false negative rate i.e. poor COVID-19 test sensitivity.
  • The diagnosis of COVID-19 should not completely rely on the RT-PCR (reverse transcriptase – polymerase chain reaction) test, at least until further test accuracy research data is available.
  • Instead, the diagnosis and management should be done based on a combination of exposure history, lung imaging findings (chest x-ray or CT scan), symptomatology, and RT-PCR.

Reality: Unclear COVID-19 test sensitivity

  • I work as an internal medicine physician in the US, and I directly take care of patients with COVID-19 infection. Over the past few weeks, my fellow physicians and myself have noted a concerningly significant number of false negatives on COVID-19 testing.
  • This raises questions regarding the sensitivity of COVID-19 RT-PCR diagnostic testing. We noted that there were a few patients who presented with symptoms concerning for COVID-19 infection, however their initial COVID-19 RT-PCR diagnostic test came back negative.
  • Over the next few days, the clinical condition of these patients deteriorated, warranting a repeat RT-PCR test that eventually came back positive.

Suggestion: Rely on the clinical picture to diagnose COVID-19

  • In the interest of public health and patient safety, I believe it is key to not miss any positive diagnoses.
  • Considering the above-mentioned concern for false negatives on COVID-19 tests, it is important to diagnose and manage the potential patients based on an overall clinical picture.
  • This should include a combination of patient’s exposure history to COVID-19, patient’s clinical symptoms (viral infection symptoms), COVID-19 RT-PCR diagnostic test, Chest X-ray or CT scan Chest findings suggestive of viral pneumonia.

How to address the possible false negative COVID-19 test?

  • If the overall clinical picture appears concerning for possible COVID-19 infection, then the patient must be managed and treated as a COVID-19 positive patient.
  • In a hospital setting, patient must be put in air-borne isolation; whereas in an outpatient setting, patient must be recommended to follow self-isolation. (Airborne vs Droplet isolation for COVID-19 is discussed in a separate blog post)
  • A repeat COVID-19 RT-PCR test must strongly be considered. Repeat testing increases the likelihood of showing a positive result if indeed the patient has COVID-19.
  • There have been instances where patients tested positive only on the 3rd or 4th COVID-19 RT-PCR test.
  • It is too much of a transmission risk if the false negatives on potential COVID-19 patients are ignored.

Current data on COVID-19 test sensitivity:

  • COVID-19 diagnostic testing in the US is currently being performed by several manufacturing companies. Considering how recent the testing is, we do not have any valid real-life research data on the sensitivity and specificity of the COVID-19 RT-PCR diagnostic test. The currently available RT-PCR test is not 100% reliable. Currently it is not possible to define the magnitude of this concern due to lack of adequate research data1.
  • A research study from China2 reported that COVID-19 RT-PCR test sensitivity was around 71%. A significant flaw in this study was that it considered CT Chest findings of viral pneumonia as a gold standard. If CT scan showed a viral pneumonia pattern, they assumed it to be due to COVID-19 infection. It is impossible to confirm a COVID-19 diagnosis based on a CT Chest findings (obviously because tens of other viruses can cause similar pneumonia pattern on the CT scan). The premise of this China study is does not serve the purpose of evaluating the sensitivity of COVID-19 RT-PCR diagnostic test. Additionally, this Chinese study looked only at 51 patients to arrive at their conclusions. Well, to say the least, I am not sold on it. 
  • Hence, until we have a concrete understanding of test sensitivity, we have to keep an open mind, perform repeat testing if needed, and manage patients as potential positives if in doubt (even though the RT-PCR is negative). There is need for large multi-centric clinical trials looking at the accuracy of COVID-19 RT-PCR test.

What are the downsides of unreliable COVID-19 test sensitivity?

  • Poor COVID-19 RT-PCR test sensitivity results in false negatives. This means that the patients who have COVID-19 infection will go undiagnosed. This can result in the following wide-scale repercussions.
  • If the test results are false negative, proper isolation techniques will not be followed. This increases disease transmission to health care workers (HCWs), and other patient’s contacts. Asymptomatic HCWs who contracted the infection can carry the infection to other patients on their panel.
  • The above-mentioned chain of events if unchecked, will result in a prolonged 2nd wave1 or eventual persistent wave of infection, and the risk of not being able to control the infection rates. 
  • A false negative patient might be at risk of not receiving any potential benefits from COVID-19 specific treatments.

Potential reasons for unreliable COVID-19 test sensitivity:

  • Low viral load during the initial stages of infection.
  • Improper test specimen collection technique3.
  • Multiple test manufacturers and lack of standardization.
  • Technological and scientific lag: We are still in the early days of COVID-19 RNA testing. 

Do not forget the basics:

  • Physical Distancing.
  • Personal Hygiene – Hand washing, etc.
  • Personal Protective Equipment – details in a separate blog post.
  • More per-capita testing – diagnostic and serology.
  • Source control.
  • Contact tracing.
  • Airborne isolation of COVID-19 positive patients / patients under investigation in a health care setting (at-least until further research is available to prove otherwise).

Learn about COVID-19 transmission on a separate blog post: How is COVID-19 Transmitted? What is the Right Mask for COVID-19? A Physician-Scientist’s Perspective.

Learn about KN95 vs. N95 Masks on a separate blog post: KN95 vs. N95 Masks – It Is Time to Use Common Sense


References:
  1. Mayo Clinic – COVID-19 Testing: The Threat of False-Negative Results
  2. Radiological Society of North America – Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR
  3. The New England Journal of Medicine – How to Obtain a Nasopharyngeal Swab Specimen

COVID-19 Test Sensitivity

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Authored by Harsha Moole, M.D., MBBS

Hey there! I hope you enjoyed reading this blog. PhysicianEstate is my brain child and passion project. I run this platform to empower entrepreneurially motivated physicians to make financially educated investment decisions and discuss asset protection strategies. Lots of important but free content here and here! If you have any questions or if you are interested in partnering with me, let’s connect! hmoole@physicianestate.com

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