Clinical implications of SARS-CoV-2 cycle threshold values in solid organ transplant recipients

Detection of SARS-CoV-2 viral RNA by RT-PCR assays is the primary diagnostic test for COVID-19. Cycle threshold (C_T ) values generated by some of these assays provide inversely proportional proxy measurements of viral load. The clinical implications of C_T values are incompletely characterized, particularly in solid organ transplant (SOT) recipients. We conducted a retrospective chart review of 25 adult SOT recipients admitted to the Yale New Haven Health System between March 1 and May 15, 2020, analyzing 50 test results to investigate the clinical implications of SARS-CoV-2 C_T values in this population. Initial C_T values from upper respiratory tract samples were significantly higher in patients on tacrolimus, but were not associated with admission severity nor highest clinical acuity. Viral RNA was detected up to 38 days from symptom onset with a gradual increase in C_T values over time. In five patients with serial testing, C_T values <35.0 were detected >21 days after symptom onset in 4/5 and ≥27 days in 2/5, demonstrating prolonged RNA detection. These data describe SARS-CoV-2 viral dynamics in SOT patients and suggest that C_T values may not be useful to predict COVID-19 severity in SOT patients. SARS-CoV-2 C_T values may be more useful in informing infection prevention measures.