BACKGROUNDHyaluronic acid (HA) fillers have increased in popularity. Although complications are rare, knowledge regarding their prevention and management are crucial. The utility of preinjection aspiration has become controversial.OBJECTIVEOur study investigated the utility of preinjection aspiration as a safety checkpoint for HA fillers through comparison of physiochemical and rheological properties in an in vitro model.MATERIALS AND METHODSWhole blood was drawn from vacutainers using syringes containing 10 commonly used HA fillers. Each HA filler was examined with the plunger pulled back at volumes of 0.2 and 0.5 cc. The time required to visualize a flash was recorded. Data were compared using physiochemical and rheological properties, pullback volumes, and needle gauges.RESULTSUsing a multivariable regression model, HA concentration, elastic modulus (G′), viscous modulus (G″), and complex modulus (G-) had significant relationships with time to flash, whereas needle gauge and pullback volume did not. However, when comparing pullback volume using an appropriate paired analysis, 0.5 cc pullback volume had a significantly decreased mean time to flash than 0.2 cc.CONCLUSIONPreinjection aspiration may have utility as a safety checkpoint for HA fillers. Practitioners may have to adjust pullback volume and waiting time to visualize the flash based on physiochemical and rheological properties.