A narrative literature review on the clinical utility of activated partial thromboplastin time and anti-factor Xa activity assays in cancer patients with anticoagulant therapy.

Background and Objective: Cancer patients face a substantially increased risk of venous thromboembolism (VTE), a leading cause of non-cancer mortality. Optimizing anticoagulation therapy in this population necessitates balancing thromboprophylaxis efficacy with hemorrhage risk, which is particularly challenging given comorbidities, polypharmacy, and tumor-specific factors such as gastrointestinal/urogenital malignancies amplifying bleeding risks with direct oral anticoagulants (DOACs). Monitoring anticoagulant activity is crucial to avoid subtherapeutic dosing or supratherapeutic dosing. This article provides a narrative review of the clinical utility of activated partial thromboplastin time (aPTT) and anti-factor Xa (anti-Xa) activity assays in anticoagulant therapy for cancer patients. Methods: A literature search was conducted in the databases of PubMed, MEDLINE, Embase, the Cochrane Library, Web of Science, and Scopus for studies published between January 2010 and August 2025. Only English-language journal articles were included. All selected publications pertained to anticoagulant therapy in cancer patients or supported the fundamental rationale and clinical management of anticoagulation. Key Content and Findings: aPTT has traditionally monitored unfractionated heparin (UFH); its limitations include variable sensitivity across anticoagulants, reagent dependency, and confounding by factors such as coagulation factor deficiencies common in liver dysfunction or malignancy itself. Conversely, anti-Xa activity assays demonstrate superior correlation with plasma concentrations of heparins [UFH, low-molecular-weight heparin (LMWH)] and factor Xa inhibitors. However, anti-Xa assays face challenges including lack of standardized reference ranges for heparins, variability at supratherapeutic concentrations, interference from concomitant medications, and insufficient evidence directly linking levels to clinical outcomes. Moreover, aPTT retains utility for UFH monitoring and provides valuable complementary information on intrinsic pathway integrity. Therefore, although anti-Xa assays are increasingly preferred for monitoring specific anti-Xa agents, aPTT remains relevant. Conclusions: A synergistic approach combining both assays, tailored to the specific anticoagulant, patient factors, and clinical context, appears optimal for evidence-based, individualized anticoagulation management in cancer patients. Future large-scale trials are needed to validate correlations between monitoring results and clinical endpoints.