Test ID: APT
Activated Partial Thromboplastin Time (APTT), Plasma
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
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
Method Name A short description of the method used to perform the test
Electromagnetic Viscosity Detection System
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
APTT (Activated Partial Thromboplastin Time)
Partial Thromboplastin Time (PTT)
Partial Thromboplastin Time, Activated
PTT (Partial Thromboplastin Time)
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Specimen Type: Platelet-poor plasma
Collection Container/Tube: Light-blue top (3.2% sodium citrate)
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
Specimen Type: Whole blood (available to local accounts only)
Container/Tube: Light-blue top (3.2% sodium citrate)
Specimen Volume: 4.5 mL
Collection Instructions: APT must be completed within 4 hours of draw.
Specimen Stability Information: Ambient
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Plasma Na Cit | Frozen | 30 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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.
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.
28-38 seconds
Interpretation Provides information to assist in interpretation of the test results
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.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
For diagnostic activated partial thromboplastin time (APTT) testing, other than heparin therapeutic monitoring, specimens should not have any residual heparin present.
Mild coagulation factor deficiency may not result in prolongation of the APTT.
APTT testing will not detect all lupus anticoagulants or coagulation inhibitors.
Mixing studies may be indicated to further evaluate specimens with an unexplained prolonged APTT.
Supportive Data
Effective February 24, 2011, Mayo's activated partial thromboplastin time (APTT) procedure was changed. Specifically, the APTT reagent was changed from Biomerieux Platelin L to HemosIL SynthASil reagent. APTT results using HemosIL SynthASil reagent are, on average, 1% higher with a R(2) of 0.7832.
-With the new reagent, the lower limit of APTT for the Stago STAR Evolution changed from 5 to 20 seconds and the upper limit will remain at 240 seconds.
-The new APTT reference range of 28 to 38 seconds was determined from a Mayo Clinic reference range study.
The heparin nomogram changed from 60 to 90 seconds to 70 to 120 seconds based on a Mayo Clinic study.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
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
Method Description Describes how the test is performed and provides a method-specific reference
The activated partial thromboplastin time (APTT) assay results are determined by mixing patient plasma with HemosIL SynthASil reagent to provide optimal and uniform activation of the sample. After activation at 37 degrees C, the reaction is initiated by the addition of HemosIL SynthASil Calcium Chloride. The time, in seconds, required for the clot formation is then measured by the STA-R Evolution analyzer. The STA-R Evolution is a fully automated coagulation instrument that uses an electromagnetic viscosity detection system. The oscillation of a steel ball within the cuvette with the reagent and plasma is monitored by the STA-R Evolution. At the constant viscosity, constant pendular swings of the ball are obtained within an electromagnetic field. As the viscosity increases as a result of the coagulation, the oscillation amplitude of the ball swing decreases. An algorithm uses these variations in oscillation amplitude to determine the clotting time in seconds. (Package insert: HemosIL SynthASil, 2008; Operators manual: STA-R Evolution)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Continuously
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
85730
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| APT | Activated Partial Thrombopl Time, P | 14979-9 |
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