ObjectiveMitochondrial DNA (mtDNA) reportedly has diagnostic and predictive value in critically ill patients. This study evaluated the diagnostic and predictive value of mtDNA in patients undergoing continuous venovenous haemofiltration (CVVH).MethodsWe consecutively enrolled 41 patients who were treated with CVVH from September 2018 to December 2019. Prefilter, postfilter, and ultrafiltrate samples were collected before the initiation of CVVH (T0) and 6 and 12 h after CVVH. The total mass removal rate (Mtr), total mass adsorption rate (Mad), plasma clearance (PC), and sieving coefficient (SC) were calculated based on the mass conservation principle.ResultsThe plasma mtDNA concentration in patients at T0 prefilter was higher than that in healthy volunteers [13.77 (12.45–15.86) vs. 1.24 (1.15–1.34) ng/mL, P < 0.001]. Prefilter, but not postfilter or ultrafiltrate, mtDNA decreased during CVVH (P = 0.02), with a total CVVH clearance of 25.9%. The postfilter and ultrafiltrate mtDNA levels were lower than the prefilter level at each time point (P < 0.05 for all). The Mtr, Mad, PC, and SC did not change over time (P > 0.05 for all).ConclusionsPlasma mtDNA in critically ill patients was significantly affected by CVVH.Trial registration: Retrospectively registered on 20 August 2019 at ClinicalTrials.gov (NCT04083482).