Current best evidence for clinical care (more info)
OBJECTIVES: To evaluate the diagnostic and prognostic performance of CT in patients referred for COVID19 suspicion to a French university hospital, depending on symptoms and date of onset.
METHODS: From March 1st to March 28th, 214 patients having both chest CT scan and reverse transcriptase polymerase chain reaction (RT- PCT) within 24?h were retrospectively evaluated. Sensitivity, specificity, negative and positive predictive values of first and expert readings were calculated together with inter reader agreement, with results of RT-PCR as standard of reference and according to symptoms and onset date. Patient characteristics and disease extent on CT were correlated to short-term outcome (death or intubation at 3 weeks follow-up).
RESULTS: Of the 214 patients (119 men, mean age 59?±?19 years), 129 had at least one positive RT-PCR result. Sensitivity, specificity, negative and positive predictive values were 79 % (95 % CI: 71-86 %), 84 %(74-91 %), 72 %(63-81 %) and 88 % (81-93 %) for initial CT reading and 81 %(74-88 %), 91 % (82-96 %), 76 % (67-84 %) and 93 % (87-97 %), for expert reading, with strong inter-reader agreement (kappa index: 0.89). Considering the 123 patients with symptoms for more than 5 days, the corresponding figures were 90 %, 78 %, 80 % and 89 % for initial reading and 93 %, 88 %, 86 % and 94 % for the expert. Disease extent exceeded 25 % for 68 % and 26 % of severe and non-severe patients, respectively (p?<?0.001).
CONCLUSION: CT sensitivity increased after 5 days of symptoms. A disease extent > 25 % was associated with poorer outcome.
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CT can be used as an adjunct tool to rule out/rule in COVID when there's a suspicion and PCR testing for COVID is not readily available. However, the sensitivity is only in the 70s for all comers which isn't great (much better with symptoms after 5 days). Specificity is better (and better than reported in other literature). The conflict with specificity in different studies does need to be resolved. However whether CT should be used as first line (esp for those being dc home) is not answered in this question. So, more studies will need to be done to show how CT can change clinical outcomes.
It is a very interesting study since we find a significant number of patients with imaging findings of COVID 19 or viral pneumonia but negative RT-PCR testing. This study highlights that there is a significant overlap of RT-PCR findings and CT findings. Similarly this article highlights a very important fact that sensitivity of CT chest findings increase with duration of onset of symptoms.
To be read with caution like all retrospective studies.