Correlation Of Chest Ct And Rt-Pcr Testing In Coronavirus Disease 2019 (Covid-19) In China: A Report Of 1014 Cases

Original Article: Tao Ai*, Zhenlu Yang*, Hongyan Hou, Chenao Zhan, Chong Chen, Wenzhi Lv, Qian Tao, Ziyong Sun, Liming Xia, Correlation of Chest CT and RT-PCR Testing in Coronavirus Disease 2019 (COVID-19) in China: A Report of 1014 Cases, Radiology

Author of summary: Laura Martin; Reviewer: Gabriele Piconi

Original Article Published on February 26th, 2020

Purpose : To investigate the diagnostic value and consistency of chest CT as compared with comparison to RT-PCR assay in COVID-19.

Methods : Study conducted using data from 1014 patients in Wuhan, China who underwent both chest CT and RT-PCR tests from January 6 to February 6, 2020.

RT-PCR results were used as reference standard, to evaluate the performance of chest CT in diagnosing COVID-19. Adding to this, for patients with multiple RT-PCR assays, the dynamic conversion of RT-PCR results (negative to positive, positive to negative, respectively) was analyzed and  compared with serial chest CT scans for those with time-interval of 4 days or more.

Results : Evaluation of the diagnostic value of chest CT as a test for COVID-19 detection:

  • Sensitivity: 97% (580/601)
  • Specificity: 25% (105/413)
  • Accuracy: 68% (685/1014)
  • Positive predictive value (PPV): 65% (580/888)
  • Negative predictive value (NPV): 83% (105/126)

In patients with negative RT-PCR results, 75% had positive chest CT findings; of them, 81% were re-classified as probable (33%) or highly likely (48%) COVID-19 cases, by the comprehensive analysis of clinical symptoms, typical CT manifestations, and dynamic CT follow-ups.

In the subgroup of positive to negative RT-PCR results, about 60% cases showed the initial chest CT had typical imaging features consistent with COVID-19 prior (or parallel) to the initial positive RT-PCR results; if we include in the statistics also patients who had initial positive chest CT scans within 6 days from the initial positive RT-PCR results, this percentage reaches 98%.

In addition, 42% cases showed improvement of follow-up chest CT scans before the RT-PCR results turning negative.

Discussion: According to current diagnostic criterion, viral nucleic acid test by RT-PCR assay plays a vital role in determining hospitalization and isolation for individual patients. However, the positive rate of RT-PCR assay for throat swab samples is reported to be around 30%-60% (in particular, in this study, around 59%).

In addition, a number of any external factors may affect RT-PCR testing results including sampling operations, specimens source (upper or lower respiratory tract), sampling timing (different period of the disease development), and performance of detection kits. As such, the results of RT-PCR tests must be cautiously interpreted, taking into consideration the medical history, clinical symptoms, typical CT manifestations and dynamic follow-ups of the patient.

On the other hand, by using RT-PCR assays with relatively low positive rate as reference, the sensitivity of chest CT for COVID-19 may be overestimated while the specificity underestimated, due to the overlap of features of COVID-19 infection and other viral pneumonia. Nevertheless, considering the rapidly spreading epidemic of COVID-19 and the priority to isolate the patients and administer appropriate treatment, the risk of diagnosing some false-positive cases by CT scan may be acceptable.

Conclusions: In spite of a low specificity, chest CT imaging has high sensitivity for diagnosis of COVID-19 and may be considered as a primary tool for the current COVID-19 detection in epidemic areas, since may be a more reliable, practical, and rapid method compared to RT-PCR. 

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