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Table 2 Evaluation of 49 patients (101 swabs) with discordant COVID-19 testing and confirmatory testing results

From: False negative rate of COVID-19 PCR testing: a discordant testing analysis

  Swab 1 (n = 49 swabs) Swab 2 (n = 49 swabs) Swab 3 (n = 3 swabs)c
NP swab in UTM (%) 29 (59.2) 32 (65.3) 2 (66.7)
Deep nasal turbinate swab (%) 20 (40.8) 9 (18.4) 1 (33.3)
Oropharyngeal swab (%) 0 8 (16.3) 0
Original swab test resulta
(E gene Ct median; range)
(RdRp gene Ct median; range)
49 negative 46 positive
3 negative
(19.5; 13.0–35.5)
(22.4; 16.2–37.8)
3 positive
0 negative
(13.9; 12.5–24.7)
(16.5; 14.8–28.0)
Positive result on E gene assayb
(Ct range)
5/49
(34.1–37.9)
0/3 ND
Positive result on CDC N1 assayb
(Ct range)
2/49
(32.7–35.9)
0/3 ND
Positive result on CDC N2 assayb
(Ct range)
5/49
(33.2–38.8)
0/3 ND
  1. Ct cycle threshold (cycles), E envelope, LDT laboratory developed test, ND not done, NP nasopharyngeal, RdRp RNA dependent RNA polymerase, UTM universal transport media
  2. aTesting done using E gene/RdRp gene LDT SARS-CoV-2 rtRT-PCR
  3. bRepeat testing conducted only on negative swabs to evaluate for false-negative results
  4. cOnly 3 of 49 patients had a third swab done