Limit of Detection, Specificity & Sensitivity There is currently a lot of debate in the medical world about how we achieve specificity (the ability to test negative), sensitivity (the ability to test positive), limit of dectection (LOD), and at what point of infection. Of course most tests will achieve high specificity and sensitivity by testing a high viral load, so we want tests that can detect them on low viral loads as well. That’s where the LOD comes into play.
This chart shows the windows that antigen and antibody tests can detect the virus. Antigen tests can detect the virus from day 0-28, but note that detection is highest between day 7-18. The key is to find tests that can still detect lower viral loads from day 0-7 (asymptomatic to the start of symptoms) at a high specificity.
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(Courtesy of @oz)
PCR tests, which can detect asymptomatic patients, are currently the most accurate (around 98%) and have a TCID:50 of about 1 x 10 to 1.8 x 10 TCID:50, which is a very good, low limit if detection that we can use as a baseline. After that PCR tests will begin to decline in accuracy. The trouble is that these PCR tests require technicians and lab equipment, hence the bottle neck effect on the healthcare system.
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The solution was to create a faster, rapid antigen test, that can still have high accuracy and low limit of detection. So far, 4 have been approved by FDA and Sona has applied to be the 5th.
Quidel Sofia 2 Rapid Antigen Test
(Requires device to read results)
Specificity: 100% clinical
Sensitivity: 80% (recently self reevaluated to 97.1%) clinical
LOD: 3.40 x 10:2 TCID:50
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BD Rapid Antigen Test
(Requires device to read results)
Specificity: 100% clinical
Sensitivity: 84% clinical
LOD: 2.8 x 10:5 TCID:50 clinical
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LumiraDX Antigen Test
(Requires device to read results)
Specificity: 97% clinical
Sensitivity: 98% clinical
LOD: 2.8 x 10:5 TCID:50 clinical
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Abbott Rapid Antigen Test
(No device required)
Specificity: 98.5% clinical
Sensitivity: 97.1% clinical
LOD: 22.5 x 10 TCID:50
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As you are about to see, Sona has a lower LOD than all these tests, with both clinical and field tests to back up their work.
Sona Nanotech Rapid Antigen Test
(No device required)
Specificity: 96.6% clinical, 90% field
Sensitivity: 96.6% clinical, 84.6% field
LOD: 2.1 x 10:2 TCID:50
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In MRIGlobal’s validation of Sona’s antigen test, they achieved 96.6% specificity and an LOD of 2.1 x 10:2 TCID:50. This is very impressive and close to PCR standards, at a much faster rate (5-15 mins)
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(Courtesy of @aegis_trader)
Sona has furthur validation from SaudiVax field studies, that resulted in 90% specificity, but did not release the LOD. The LOD for Sona’s field studies has been rumoured to be very low, just like the clinical study at MRI Global.
Jim Megann, director, has went on record saying the viral loads were very low, in fact, lower than they expected in the field studies.
Darren Rowles, CSO, also said in the last news release “Rapid, point-of-care, antigen tests can make a significant contribution to reducing the spread of COVID-19 by detecting the presence of the virus, potentially before the onset of symptoms. This achievement is the result of the extraordinary work and dedication by the entire Sona team and our partners.”
Detecting the virus before the onset of symptoms would require a low viral load.
SaudiVax and associates have shown great confidence in Sona’s test and have tweeted openly about it.
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(Courtesy of @woodywoodland)
Now that validation and field studies are complete and Sona has submitted to FDA and HC with their final submission, I predict a fast approval from both regulatory bodies, which will give the green light for mass manufacturing and sales.
Put on your seat belt.