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7 votes

Can a RT-PCR test claim 100% sensitivity and specificity?

A diagnostic test should never claim 100% sensitivity or specificity. So we are all on the same page, let's review what sensitivity and specificity actually mean. According to the US Food and Drug ...
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4 votes

Why are COVID nucleic acid tests sometimes reported with non-integer CT values?

Viral nucleic acid amplification tests use real time PCR to detect viral genomic material. If the genetic material is present, a reaction will occur that generates fluorescence. If sample produces a ...
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4 votes
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Antigen vs PCR test

The ratio of false positives to true positives (as well as overall "accuracy") is a function of the underlying rate in the population. Let's imagine you have a test that has 95% specificity. ...
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3 votes

Having tested positive for COVID-19, will future tests be positive?

There are two general categories of tests typically used for identifying viral infections: those based on viral genetic material and those based on host immune response. The CDC page on MERS-CoV ...
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2 votes
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Has China announced any results from their massive (new) COVID-19 testing program in Wuhan?

From Time: June 3, 2020 Wuhan Tests Nearly 10 Million People in 19 Days, Finding Just 300 Coronavirus Infections (BEIJING) — The Chinese city of Wuhan, where the coronavirus was first detected ...
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2 votes

Has China announced any results from their massive (new) COVID-19 testing program in Wuhan?

The results are probably in the Chinese press, but are being reported elsewhere China has reported 51 new coronavirus cases including 40 asymptomatic infections, majority of them in the contagion’s ...
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2 votes

How do they test COVID-19 in drive-thru labs?

I cannot answer about South Korea, but as far as other drive-in test stations are concerned the rules I've seen are: Call ahead to get checked whether testing is indicated, get issued a special ...
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2 votes
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Do presymptomatic people test PCR-positive

Presymptomatic patients with coronavirus may test positive with RT PCR (see: Kim, Jeong et al. Viral kinetics of SARS-CoV-2 in asymptomatic carriers and presymptomatic patients. Int J Inf Dis Vol.95, ...
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2 votes
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How long it will take for a RT-PCR test CT value to go to from 27 to 35?

It is difficult to be sure from your question, but you may have a slight misunderstanding of "Ct" value. Ct stands for cycle threshold¹. In a real time polymerase chain assay, a sample is ...
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1 vote

Antigen vs PCR test

Bryan is correct, especially in his comment in the case of 0% true/prior prevalence 40/1000 = 4% positive. 1-2/40 = 2.5-5%. But even in such a conditioned test scenario, in which the 2nd test is ...
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1 vote
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False Positive PCR - COVID-19 and possible reinfection when antibodies value is +7.0

The rt-PCR tests for Covid-19 are not 100% specific so yes it's possible to get a false positive. From the China PCR test The sensitivity of the RT-PCR diagnostic test was estimated to be 0.777 (...
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1 vote

Why does CDC's RT-PCR protocol for Covid-19 use the N gene, but the Charite one the E gene and RdRp?

Well, this is the explanation I found in a (different) CDC paper: First, we based assay designs on previous diagnostic assays that had been developed for detection of MERS-CoV (12) and SARS-CoV (10)...
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1 vote

How often is a Ct of 30 (or more) using the Charité protocol a false positive for Covid-19?

Well, interpreting the Charité numbers is still a bit of a mystery to me, but by analogy with a US case, having some tests close to the detection limit for Covid-19 is not so unusual in some ...
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