The act test uses a tube containing
For increased levels:
- Patients receiving heparin which binds to antithrombin to inhibit clotting factors mainly of the intrinsic pathway.
- Patients receiving warfarin (Coumadin) which reduces the functional activation of vitamin K dependent clotting factors
- Cirrhosis which results in decreased production of clotting factors
- A deficiency in clotting factors.
- Lupus anticoagulants against components involved in the activation of the coagulation cascade
Assess the patient to detect possible bleeding including blood in the urine and the presence of bruises, petechiae, and/or low back pain.
For decreased levels:
- Activate of the thrombotic pathways can shorten the ACT.
Related Tests
- Partial Thromboplastin Time (PTT)
- Prothrombin Time
- Coagulating Factor Concentration
Lab Interactions
The ACT can be affected by several biologic variables, including:
- Hypothermia
- Hemodilution
- Platelet number & functions
- Factors affecting the pharmacokinetics of heparin (e.g., kidney or liver disease)
- Antithrombin (AT) deficiency
- A partially or completely occluded specimen can increase ACT measurements
- Black top tube containing a particulate activator
Lab Procedure
- If the patient is receiving a continuous heparin drip, the blood sample is obtained from the arm without the intravenous catheter
- Less than 1 ml of blood is collected into a commercial container.
- The container is placed into a whole blood micro-coagulation analyzer.
- When a clot has formed, the ACT value is displayed on the machine's panel.
- Apply pressure to the venipuncture site after procedure. Remember that the bleeding time will be prolonged because of anticoagulation therapy.
- For clinical significance, the test results must be correlated with the time of the heparin administration. A clinical flow sheet is used to list the test results with the time and route of heparin administration.
Storage & Handling
- The sample should not be stored. It should be tested immediately after it has been obtained.
Patient Counseling
- No preparation needed by the patient.
References
- LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests. First ed. Montvale, NJ: Thomson PDR; 2007.
- Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5 th Ed. St. Louis, Missouri. 2014.
- Olson JD et al. College of American Pathologists Conference XXXI on Laboratory Monitoring of Anticoagulant Therapy. Laboratory monitoring of unfractionated heparin therapy. Arch Pathol Lab Med 1998;122(9):782-98. PMID: 9740136
