Background <p>Activated clotting time (ACT), a widely used point-of-care test, monitors anticoagulation in clinical settings. Despite ACT technology advancements, some uncertainties remain regarding the factors influencing ACT measurements and inter-device variability. Although ACT is widely used for anticoagulation monitoring in clinical practice, the factors affecting ACT values are not fully understood, complicating their interpretation. This scoping review aims to address these challenges by examining the factors affecting ACT measurements, highlighting gaps in current knowledge.</p> Methods <p>A systematic search was conducted in MEDLINE (PubMed), including animal studies, clinical trials, observational studies, in vitro experiments, and systematic reviews. Article selection involved a two-step process: initial title and abstract screening followed by a full-text review, this was performed by three independent reviewers. Data from the included studies were charted and extracted, collecting information on factors influencing ACT measurements.</p> Results <p>A total of 1908 records were identified, with 74 studies included after screening. Key factors influencing ACT measurements included platelet count, platelet inhibitors, and hematocrit levels. Direct thrombin inhibitors, low-molecular-weight heparin, and direct oral anticoagulants prolonged ACT with characteristics different from heparin. Aprotinin and nafamostat mesylate interacted with coagulation activators during ACT measurements affecting results. Significant differences in ACT measurements were observed between devices.</p> Conclusions <p>This scoping review comprehensively analyzed factors influencing ACT and emphasized ACT measurement variability across devices. Despite its widespread use as a point-of-care test for anticoagulation monitoring, ACT’s limitations and device discrepancies highlight the need for cautious interpretation in clinical settings.</p> Clinical trial number <p>Not applicable.</p>