Hemolysis testing in circulatory support pumps: Standards, mock loops, and pulsatility

Hemolysis evaluation is central to the safety assessment of blood pumps and extracorporeal circulatory support, yet clinically relevant hemolysis continues to occur despite widespread use of standardized in vitro frameworks. A major contributor to this gap is that LVAD and VA-ECMO operate under intrinsically pulsatile and transient hemodynamic conditions that are not fully represented by steady or quasi-steady test protocols. This narrative, methods-focused review synthesizes recent in vitro hemolysis testing literature with an emphasis on pulsatility-aware evaluation. We highlight limitations of conventional large-volume loops and summarize emerging approaches that enable more interpretable benchmarking, including reduced-volume paired-loop testing, hybrid mock circulatory loops (HMCL) that reproduce heart-pump interaction, and quantitative descriptors for defining pulsatility. In addition, key operating and blood-handling descriptors required for reproducible interpretation across test platforms are organized to clarify minimum reporting requirements. Together, these considerations support the development of in vitro hemolysis evaluation frameworks that better reflect clinical operating conditions and facilitate objective comparison of pulsatile blood-pump technologies.