Activated Partial Thromboplastin Time


  • EPIC Code:
  • LAB325
  • Soft Test Code:
  • PTT
Alternate Names
  • APTT
  • Partial Thromboplastin Time
  • PTT
Clinical Significance

Screening for deficiencies or inhibitors of the coagulation system. 
Monitor the dosing effect of unfractionated heparin therapy.

Specimen Collection & Preparation

Client Notes:

If patient is on Unfractionated Heparin the specimen will need to be to the testing laboratory within 45 minutes of collection.  

Specimen Requirements

2.7 mL Whole Blood in a Blue Top Tube - 3.2% Buffered Sodium Citrate

Alternate Specimen

2.7 mL Whole Blood in a full Blue Top Tube - 3.2% Buffered Sodium Citrate in a Plastic Vial when unable to send to testing laboratory within the transport stability levels.



Unfractionated heparinized patient 4 hour Ambient 

Non-heparinized patient 24 hours Ambient 

Collection Instructions

Specimens must be filled appropriately see this example

Correct ratio of Blood to Citrate is critical (9:1). Specimens must be filled within +/- 10% of stated volume.

If a Blue Top Tube is collected utilizing a butterfly, a Blue Discard Tube must be drawn first to remove air from the line. If this is not done, the Blue Top Tube will not be filled properly due to the vacuum in tube and a redraw will be required

   Heparinized Patient specimens must be spun within 1 hour of collection - Follow Platelet Poor Collection

Note: Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. 
If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution should be considered. 
When obtaining specimsn from indwelling lines that may contain heparin, the line should be flushed with 5mL of saline, and the first 5 mL of blood or 6-times the line volume
(dead space volume of the catheter) be drawn off and discarded before the coagulation tube is filled. For those samples collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.

Clinical Interpretation

Reference Range:

24.2 - 33.0 seconds

Therapeutic range for pre-mixed heparin is 50.0-70.0 seconds.  seconds. Heparin therapeutic range is based on the APTT range corresponding to a heparin concentration of 0.3 to 0.7 Units/milliliter determined by Factor Xa inhibition assay.

Critical Ranges:

>= 110.0 Seconds

  • Photo Optical

Clinical Significance

Screening for deficiencies or inhibitors of the coagulation system. 
Monitor the dosing effect of unfractionated heparin therapy.

Production Schedule

Sites Performed
  • Parkview DeKalb Hospital
  • Parkview Huntington Hospital
  • Parkview Kosciusko Hospital
  • Parkview LaGrange Hospital
  • Parkview Noble Hospital
  • Parkview Randallia Hospital
  • Parkview Regional Medical Center
  • Parkview Southwest
  • Parkview Wabash Hospital
  • Parkview Whitley Hospital
Days Performed
  • Coagulation
Turn Around Time

8 hours

Stat Eligible

Coding & Compliance



CPT Coding


Medical Necessity May Apply