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Test Code APTTP Activated Partial Thromboplastin Time (APTT), Plasma

Useful For

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

Method Name

Coagulometric (Turbidimetric)

Reporting Name

Activated Partial Thrombopl Time, P

Specimen Type

Plasma Na Cit

Specimen Required

Specimen Type: Platelet-poor plasma

Collection Container/Tube: Light-blue top (3.2% sodium citrate)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Spin down, remove plasma and spin plasma again.

Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Plasma Na Cit Frozen (preferred) 30 days
  Ambient  4 hours

Reject Due To


Mild OK; Gross reject


Mild OK; Gross OK


Mild OK; Gross OK



Clinical Information

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).


Effective November 2016, APTT will no longer be used as the primary method for therapeutic heparin monitoring, for that purpose, order the heparin anti-Xa assay HEPTP / Heparin Anti-Xa Assay, Plasma.

Reference Values

25-37 seconds


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.


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

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

Method Description

Coagulometric (turbidimetric) clot detection is based on the principle that light passing through a medium in which fibrinogen is converted to fibrin is absorbed by the fibrin strands. Light at 671 nm is transmitted through a sample onto a photodetector, which is positioned 180 degrees to the source. Light absorption increases as fibrin clot formation progresses. Consequently, light transmittance through the sample continuously decreases and is measured by the photodetector. The corresponding electrical signal output from the photodetector changes according to the detected light. The signal output is processed via software through a series of algorithms to determine the clot point.


In this test, the incubation of plasma sample with an optimal quantity of phospholipid, a negatively charged contact activator, and buffer initiates the activation of the intrinsic coagulation pathway. After incubation at 37° C, calcium is added to trigger the coagulation process and the time required for clot formation is measured. The activated partial thromboplastin included in the SynthASil kit is a liquid buffered reagent that contains synthetic phospholipid for optimal platelet-like activity and highly defined nonsettling colloidal silica for optimal activation of the contact phase of coagulation.(Package insert: HemosIL SynthASil; IL ACL TOP Operator's Manual)

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Analytic Time

Same day/1 day

Specimen Retention Time

24 hours

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
APTTP Activated Partial Thrombopl Time, P 14979-9


Result ID Test Result Name Result LOINC Value
APTTP Activated Partial Thrombopl Time, P 14979-9