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Test Code 025 Activated Partial Thromboplastin Time (APTT)

Additional Codes


PowerChart: PTT

MA Cerner: Activated PTT.

Specimen Requirement

BD sodium citrate blue-top tube filled to or above the etched line on the tube.


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

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.


If the testing is not completed within 4 hours the plasma should be removed from the cells and transferred to a plastic tube. Samples are frozen at -20° C for up to two weeks.



  • 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 lines.
  • 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 flush.

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

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. 


Testing is performed Monday through Sunday.

Routine orders: Typically completed within 4 hours; Mercy DV and MA West within 24 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.

CPT Code Information

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

LOINC Code Information

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

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.

Test Method

Clot Based Assay; ACL Systems