Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

APT
9058
APCRV
81967
Activated Partial Thromboplastin Time (APTT), Plasma
Clinical Information: The activated partial thromboplastin time (APTT) test reflects the activities
of most of the coagulation factors, including factor XII and other "contact factors" (prekallikrein [PK]
and high molecular weight kininogen [HMWK]) and factors XI, IX, and VIII in the intrinsic
procoagulant pathway, as well as coagulation factors in the common procoagulant pathway that include
factors X, V, II and fibrinogen (factor I). The APTT also depends on phospholipid (a partial
thromboplastin) and ionic calcium, as well as an activator of the contact factors (eg, silica), but reflects
neither the extrinsic procoagulant pathway that includes factor VII and tissue factor, nor the activity of
factor XIII (fibrin stabilizing factor). The APTT is variably sensitive to the presence of specific and
nonspecific inhibitors of the intrinsic and common coagulation pathways, including lupus
anticoagulants or antiphospholipid antibodies. Lupus anticoagulants may interfere with in vitro
phospholipid-dependent coagulation tests, such as the APTT, and prolong the clotting time. Lupus
anticoagulants are antibodies directed towards neoepitopes presented by complexes of phospholipid and
proteins, such as prothrombin (factor II) or beta 2 glycoprotein I, but these antibodies do not specifically
inhibit any of the coagulation factors. Clinically, lupus anticoagulant represents an important marker of
thrombotic tendency. In contrast, patients with specific coagulation inhibitors, such as factor VIII
inhibitor antibodies, have a significant risk of hemorrhage and often require specific treatment for
effective management. Both types of disorders may have similar prolongation of the APTT.
Useful For: Monitoring heparin therapy (unfractionated heparin [UFH]) Screening for certain
coagulation factor deficiencies Detection of coagulation inhibitors such as lupus anticoagulant, specific
factor inhibitors, and nonspecific inhibitors
Interpretation: Since activated partial thromboplastin time (APTT) reagents can vary greatly in their
sensitivity to unfractionated heparin (UFH), it is important for laboratories to establish a relationship
between APTT response and heparin concentration. The therapeutic APTT range in seconds should
correspond with an UFH concentration of 0.3 to 0.7 U/mL as assessed by heparin assay (inhibition of
factor Xa activity with detection by a chromogenic substrate). In our laboratory, we have found the
therapeutic APTT range to be approximately 70 to 120 seconds. Prolongation of the APTT can occur as
a result of deficiency of 1 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. 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.
Reference Values:
28-38 seconds
Clinical References: 1. Miletich JP: Activated partial thromboplastin time. In Williams
Hematology. 5th edition. Edited by E Beutler, MA Lichtman, BA Coller, TJ Kipps. New York,
McGraw-Hill, 1995, pp L85-86 2. Greaves M, Preston FE: Approach to the bleeding patient. In
Hemostasis and Thrombosis: Basic Principles and Clinical Practice. 4th edition. Edited by RW Colman,
J Hirsh, VJ Marder, et al. Philadelphia, JB Lippincott Co, 2001, pp 1197-1234 3. Olson JD, Arkin CF,
Brandt JT, 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;122:782-798
Activated Protein C Resistance V (APCRV), Plasma
Clinical Information: Protein C, a part of the natural anticoagulant system, is a vitamin
K-dependent protein zymogen (molecular weight=62,000 da) that is synthesized in the liver and
circulates at a plasma concentration of approximately 5 mcg/mL. Protein C is activated to activated
protein C (APC) via proteolytic cleavage by thrombin bound to thrombomodulin, an endothelial cell
surface membrane protein. APC downregulates the procoagulant system by proteolytically inactivating
procoagulant factors Va and VIIIa. Protein S, another vitamin K-dependent coagulation protein,
Current as of January 3, 2013 2:22 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 45