Settings in which anti-Xa monitoring is preferred
| Critically ill children and adults |
| Presence of lupus anticoagulant |
| Pregnancy |
| Deficiencies of contact system factors (factor XII, kallikrein, high-molecular-weight-kininogen) |
| Special populations receiving low-molecular-weight heparin |
| Suspected heparin resistance: |
| > 35,000 U of unfractionated heparin required over 24 hours, or total daily dose exceeding estimated weight-based requirement |
| Antithrombin deficiency |
| Increased heparin clearance |
| Concomitant use of aprotinin and nitroglycerin |