When the answer is a maybe: a retrospective review of indeterminate SARS-CoV-2 results and their associations

Abstract

Testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using reverse transcriptase polymerase chain reaction (RT-PCR) may generate indeterminate results (with a cycle threshold ≥30), requiring further investigation to determine the clinical significance. Patient variables which could predict a definitive result ('Detected'/'Not detected') post indeterminate result would aid in optimization of bed management and utilization of limited resources. A retrospective observational study of indeterminate SARS-CoV-2 results in an Irish tertiary hospital from March 2020 to March 2022 was performed to determine whether demographics, comorbidities and immunosuppression were associated with a definitive result upon subsequent investigation. Data was obtained from patient and laboratory records. Analysis of association was explored using Fisher's exact test, and predictability was tested using logistic regression. Of 411 patients with an initial indeterminate test, investigation showed that 299 (72.2%) patients had a subsequent definitive result; 29 were Detected and 270 were Not detected. In the Detected group, a prior diagnosis of COVID-19 was associated with a reduced risk of becoming Detected (crude odds ratio (COR) = 0.10, 95% CI 0.03-0.35). In the Not detected group, vaccinated patients were less likely to have a Not detected result on subsequent testing (adjusted odds ratio (AOR) = 0.57, 95% CI 0.34-0.94). Patients with previous COVID-19 infection were less likely to have a Detected result and vaccinated patients were less likely to have a Not detected result upon investigation of an indeterminate result. This study emphasizes the need for a good clinical and medical history in the management of SARS-CoV-2.

Keywords: COVID-19; Cycle threshold; High Ct; RT-PCR; SARS-CoV-2.