Threshold for cytomegalovirus DNA PCR for preemptive treatment after allogeneic stem cell transplantation

This study evaluated cytomegalovirus (CMV) reactivation after allogeneic stem cell transplantation (allo-SCT) using both CMV-PCR and antigenemia assays in 109 adult recipients. CMV-PCR and antigenemia values had a moderate linear correlation. In total, 58 patients exhibited CMV-PCR positivity before starting antigenemia-based preemptive treatment. Excluding the two patients with persistent PCR positivity, the antigenemia value subsequently reached the threshold in 31 of 54 patients. On the other hand, 25 patients had spontaneous clearance of viremia without preemptive treatment. Spontaneous clearance was associated with letermovir use and the absence of graft-versus-host disease. The clinical course of CMV infection was simulated using various CMV-PCR thresholds (range 50-1000 IU/mL). In high-risk patients not treated with letermovir, a threshold of 50 IU/mL enables preemptive treatment initiation without increasing overtreatment risk in patients with spontaneous clearance. However, in high-risk patients treated with letermovir, thresholds > 150 IU/mL delayed the start of preemptive treatment. In low-risk patients, a threshold of 500-750 IU/mL balances avoiding spontaneous resolution and increasing delayed treatment. PCR thresholds of 50 and 150 IU/mL may be appropriate for initiating preemptive therapy in high-risk patients treated and not treated with letermovir, respectively, while 500-750 IU/mL may be optimal for low-risk patients.