APTT

PTT, APTT, aPTT, Partial Thromboplastin Time, Activated Partial Thromboplastin Time (APTT) 

Test Codes

EPIC: LAB325

Department

Coagulation

Instructions

Specimens with hematocrit values greater than 55% have spuriously increased aPTT values. To correct for this, specimens should be re-collected using a specified whole blood to sodium citrate ratio. Contact the performing Laboratory for specific instructions.

Specimen Collection Criteria

Collect: One Light Blue-top 3.2% Sodium Citrate tube.

• TUBE MUST BE FULL.
• Greiner brand tubes must be filled to the black arrow.
• See Minimum Pediatric Specimen Requirements.
• Requests for an add-on aPTT for patients on Heparin must be within one hour of specimen collection time. 

Physician Office/Draw Specimen Preparation

For optimal results, maintain whole blood specimen at room temperature (20-26°C or 68-78.8°F) prior to transport. Transport whole blood to the Laboratory within 16 hours of collection. If transport within 16 hours is not possible, the following procedure must be followed for accurate results:

1. Centrifuge the capped tube at 1500 x g for 15 minutes.
2. Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.
3. Immediately remove only the top two-thirds of the PPP and transfer it into a plastic tube.
4. Freeze (-20°C/-4°F or below) the PPP immediately.
5. Transport frozen on DRY ICE. Specimen must remain frozen during transport.

For Outreach Patients Only:
Prolonged aPTTs in specimens greater than 16 hours old from patients NOT on anticoagulants should be verified by repeat analysis on a frozen specimen.

Preparation for Courier Transport

Transport: Whole blood at room temperature (20-26°C or 68-78.8°F), or plasma obtained through the process listed above, frozen (-20°C/-4°F or below).

Rejection Criteria

• Glass tubes and 3.8% Sodium Citrate tubes.
• Specimens that are clotted or grossly hemolyzed.
• Inappropriate specimen volume.
• Thawed or partially thawed specimens. 

In-Lab Processing

Whole blood specimens must be processed as follows upon receipt in the Laboratory:

1. Centrifuge the capped tube at 1500 x g for 15 minutes.
2. Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10.0 bil/L. Plasma with a platelet count of less than 10.0 bil/L is critical for accurate results.
3. Immediately remove only the top two-thirds of the PPP and transfer it into a plastic tube.
4. Test or freeze specimen according to lab protocol.

Storage

Whole Blood (spun or unspun)

Inpatients
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Outreach Only
Room Temperature (20-26°C or 68-78.8°F): 16 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Plasma Aliquot

Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): 30 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 5 days
Room Temperature (20-26 C or 68-78.8 F): 5 days 

Laboratory

Canton Laboratory
Dearborn Hematology Laboratory
Farmington Hills Hematology/Coagulation Laboratory
Grosse Pointe Hematology/Urinalysis Laboratory
Lenox Main Laboratory
Livonia Main Laboratory
Royal Oak Coagulation Laboratory
Taylor Hematology Laboratory
Trenton Hematology/Coagulation Laboratory
Troy Hematology/Coagulation Laboratory
Wayne Hematology/Coagulation Laboratory

Performed

Sunday – Saturday, 24 hours a day.
STAT results available within 45 minutes of receipt in the Laboratory unless further verification is necessary.
Routine results available within 2 hours of receipt in the Laboratory.

Reference Range

aPTT: 25-38 seconds. 

Heparin Therapeutic Range:

• Acute Coronary Syndrome: 55-75 seconds.
• Venous Thromboembolism: 60-90 seconds.

Test Methodology

Photo-Optical Clot Detection (IL ACL-TOP Series)

Interpretation

• In patients receiving oral anticoagulants, the circulating levels of factors II, VII, IX, and X are depressed. The aPTT is expected to be prolonged in these patients.
• The presence of nonspecific inhibitors, such as the lupus-like anticoagulant, may prolong the aPTT, but this effect is variable. In this case, the prolonged clotting time may be related to the nature of the aPTT reagent used in the assay.
• The aPTT may be affected by a number of drugs. A decrease in aPTT has been reported with conjugated estrogen therapy or oral contraceptives. An increase in aPTT has been seen in diphenylhydantion, heparin, warfarin, naloxone, and radiographic agent administration.

Clinical Utility

• The Activated Partial Thromboplastin Time (aPTT) employs the intrinsic pathway of clotting. A lipid factor, similar to that released by the platelets, and calcium are added to the plasma. Plasma Thromboplastin is formed which initiates the clotting mechanism. The APTT has also been widely advocated as a means to monitor the effectiveness of unfractionated heparin therapy, where the clotting time is prolonged in proportion to the level of unfractionated heparin. The ACCP and CAP recommend that the aPTT therapeutic target be established as comparable to 0.3 to 0.7 U/mL unfractionated heparin by anti-Xa assay.
• The aPTT assay aids in the evaluation of the intrinsic coagulation system issued to monitor heparin therapy, aids in screening for the presence of classical hemophilia A and B, aids in the diagnosis of congenital deficiencies of factors II, V, VIII, IX, X and XI, XII, dysfibrinogenemia, disseminated intravascular coagulation, liver failure, congenital hypofibrinogenemia, vitamin K deficiency.

CPT Codes

85730

LOINC: 14979-9

Contacts

Last Updated

9/12/2025