Test Catalog

Test ID: APTTP    
Activated Partial Thromboplastin Time, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

Monitoring heparin therapy (unfractionated heparin)


Screening for certain coagulation factor deficiencies


Detection of coagulation inhibitors such as lupus anticoagulant, specific factor inhibitors, and nonspecific inhibitors

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

The activated partial thromboplastin time (APTT) assay is used as a screening test to evaluate the overall integrity of the intrinsic/common coagulation pathway and to monitor patients on heparin therapy.


This test reflects the activities of most of the coagulation factors in the intrinsic and common procoagulant pathway, but not the extrinsic procoagulant pathway, which includes factor VII and tissue factor, nor the activity of factor XIII (fibrin stabilizing factor).

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

25-37 seconds

Interpretation Provides information to assist in interpretation of the test results

Prolongation of the activated partial thromboplastin time (APTT) can occur as a result of deficiency of one or more coagulation factors (acquired or congenital in origin), or the presence of an inhibitor of coagulation such as heparin, a lupus anticoagulant, a nonspecific inhibitor such as a monoclonal immunoglobulin, or a specific coagulation factor inhibitor. Prolonged clotting times may also be observed in cases of fibrinogen deficiency, liver disease, and vitamin K deficiency.


Shortening of the APTT usually reflects either elevation of factor VIII activity in vivo that most often occurs in association with acute or chronic illness or inflammation, or spurious results associated with either difficult venipuncture and specimen collection or suboptimal specimen processing.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Activated partial thromboplastin time (APTT) results may be affected by many commonly administered drugs and should be considered as a potential source of unexpected abnormal results.


APTT testing will not detect all lupus anticoagulants, antiphospholipid antibodies, or coagulation inhibitors. SynthASil reagent is reportedly sensitive to decreased concentration of intrinsic factors resulting in an abnormal APTT value when factors VIII, IX, XI, and XII levels were in the 35% to 60% range.


Mixing studies may be indicated to further evaluate specimens with an unexplained prolonged APTT.

Supportive Data

The activated partial thromboplastin time (APTT) reference interval of 25 to 37 seconds was determined by verifying the IL package insert.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Clinical and Laboratory Standards Institute (CLSI). One-stage PT and APTT test; Approved Guideline Second Edition. H47-A2, 2008

2. Greaves M, Preston FE: Approach to the bleeding patient. In Hemostasis and Thrombosis: Basic Principles and Clinical Practice. Fourth edition. Edited by RW Colman, J Hirsh, VJ Marder, et al. Philadelphia, JB Lippincott Co, 2001, pp 1197-1234

3. Boender J, Kruip MJ, Leebeek FW: A Diagnostic Approach to Mild Bleeding Disorders. J Thromb Haemost 2016;Aug;14(8):1507-1516. doi: 10.1111/jth.13368