Methods: 
For the study, patients who came for routine control between September 2020 and March 2021 in Ankara City Hospital Liver Transplant outpatient clinic were screened. All patients were older than 18 years of age and had undergone LT in the past. The ethics committee approved the study of Ankara Bilkent City Hospital (Approval number: E2-21-280 ). The study was conducted in accordance with good clinical practice principles and the Declaration of Helsinki.
Study enrolment was performed when patients presented for scheduled routine follow-up. Among all patients, patients whose serum COVID-19 IgM + IgG antibody was tested were recorded. Sars-Cov-2 polymerase chain reaction (PCR) test was performed with a nasopharyngeal-oropharyngeal swab in each patient with a positive antibody test within the first three days the results. All participants completed a questionnaire querying information including common clinical symptoms (fever, cough, diarrhea, myalgia, nausea, and vomiting) in the last six months. Additionally, we questioned all participants for a history of contact with a covid-19 positive patient or hospitalization.
We evaluated the performance of COVID-19 serology testing on chemiluminescent immunoassay (CLIA) per manufacture’s protocol (ADVIA Centaur®) SARS-CoV-2 Total (COV2T) (Siemens Healthcare Diagnostics Inc., NY, USA) (Siemens Test). These serological tests use the SARS-CoV-2 Spike protein (S protein) as a viral labeling protein to detect anti-SARS-CoV-2 antibodies. Test results were interpreted as positive if the signal value of the Siemens Test (index) ≥1.0 of total antibodies. All serum Anti-SARS-CoV-2 Total results of all patients were collected before the vaccination for COVİD-19.
The statistical analyses were performed with IBM SPSS Statistics for Windows, Version 26.0 software (IBM Corp., Armonk, NY, USA). Continuous variables were expressed as median and range. Categorical variables were summarized as count and percentage. Between-group comparisons were performed using the Mann-Whitney U test for continuous variables and a chi-squared test (or Fisher’s exact test where appropriate) for categorical variables. P values are given as indicated using the x2 test or a non-parametric t-test. A p-value <0.05 was considered to indicate statistical significance.