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Test Code PTT Activated Partial Thromboplastin Time (APTT) LAB325

Test Method

Clot Based Assay; ACL Systems


Testing is performed Monday through Sunday.

Routine orders: Typically completed within 4 hours.

Expedite orders: Typically completed within 1 hour after the
specimen arrives at the testing site.

STAT orders: Typically completed within 25 minutes after the
specimen arrives at the testing site.

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. 

Specimen Requirement

Sodium citrate blue-top tube filled to the area within the
indicator arrow printed on the side of the tube.

CPT Code Information

85730 Coagulopathy Testing: Thromboplastin
time, partial (PTT); plasma or whole blood

Reference Values

25-37 Seconds for Non-anticoagulated samples

  • Critical Value: > 100 Seconds

Therapeutic Range: 44-74 Seconds

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 0.2 to 0.4 U/mL as assessed
by heparin response curve. In our laboratory, we have found the
therapeutic APTT range to be approximately 44 to 74 seconds.

LOINC Code Information

14979-9 Activated Partial Thromboplastin Time (aPTT) In Platelet
Poor Plasma By Coagulation Assay

Additional Specimen Collection Information


Invert the sodium citrate tube end to end 4 times to
thoroughly mix blood and anticoagulant. The tube should be left
stoppered until time of testing. Specimens stored at room
temperature should be centrifuged and tested within four hours of
specimen collection.



  • It is not recommended to use a winged blood
    collection set (Butterfly).
  • If a vacuum tube butterfly must be used, the first tube in the
    series will be under-filled. Collect a “discard citrate
    tube”, and then collect the citrate tube used for testing.
    This will ensure the proper blood to anticoagulant ratio.
  • If using a syringe, use a BD Blood Transfer Device to transfer
    blood from the syringe to the citrate tube within one minute of
    collection. Hold the syringe with the plunger in the up-right
    position and allow the vacuum present to fill the tube. Before
    collection, be sure the syringe plunger is pushed to the top of the
    syringe. The transfer device may pop up and needs to be
    held down to completely fill tube to between fill
  • Do not “force fill” blood into a vacuum tube. This
    may result in activation of the platelets possibly leading to
    erroneous results. Allow the vacuum present to fill the tube.
  • Do not remove vacuum tube cap to add blood.
  • Specimens should be obtained from a single venipuncture with
    minimal tissue trauma. Never combine multiple blood collections
    into a single vacuum tube.
  • Never re-use a syringe that was used for a pic line saline

Refer to the “Citrated Plasma for Coagulation Studies” protocol
in the Quality Assurance Manual.