Synonym

• APTT
• Partial thromboplastin time
• PTT

Tubes

• Light blue top (citrate) tube
• Fill tube to maximum draw

Additional information on specimen collection:

• Mix well. Do not centrifuge
• Reject:
• Grossly hemolyzed specimen
• Frozen specimen that has thawed during transport
• Clotted specimen
• Specimen collected in tube other than that containing 3.2% citrate as anticoagulant
• Specimen received more than 2 hrs after collection

Info

Activated Partial Thromboplastin Time (aPTT) test is done to evaluate blood coagulation disorders; especially of the intrinsic coagulation pathway. It measures the length of time (in seconds) required for clotting to occur when certain reagents are added to plasma.

This test is most commonly used to monitor heparin therapy; but can also be used to investigate a bleeding or thrombotic condition.

Clinical

The aPTT test should not be used as a routine general screening test. It should be performed to:

• Evaluate patients with bleeding episodes
• Evaluate patients with thromobotic episodes
• Evaluate risk of excessive bleeding (before a surgery)
• Monitor anticoagulant therapy (heparin therapy)

aPTT evaluates all clotting factors except the factor VII and factor XIII (intrinsic pathway). It does not however, reflect the platelet function.

Monitoring heparin therapy:

• When used for monitoring heparin therapy, aPTT should typically be performed every 6 hours, until the desired therapeutic range is reached (2-3 times control)
• aPTT values should be maintained at 3 times the control value by heparinization for 18 to 24 hours after a percutaneous transluminal coronary angioplasty (PTCA)
• When heparin is given in large volumes, as during cardiopulmonary bypass, the activated clotting time (ACT) is a preferred test for monitoring heparin therapy.

In order to differentiate between coagulation factor deficiencies and the presence of coagulation factor inhibitors like antifactor antibodies, mixing studies may be performed.

The clotting time can be corrected by mixing the patient's clotting factor deficient plasma with normal plasma. However, if the prolonged aPTT is due to coagulation factor inhibitors, there will be no correction in mixing studies.

Nl Result

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

Quantitative

• Normal: 25-39 seconds
• Therapeutic: Depending upon indication, typically 2-3 times the control value

High Result

Increased aPTT will occur in the following conditions:

• Afibrinogenemia
• Antiphospholipid antibody syndrome
• Cholangiocarcinoma
• Copper deficiency (Severe)
• Deficiencies of Prekallikrein and kininogens
• Disseminated intravascular coagulation (DIC), but may be normal in chronic DIC
• Factor deficiencies
• Hemophilia A (factor VIII deficiency)
• Hemophilia B (factor IX deficiency)
• Factor XII (Hageman Factor) deficiency
• Factor XI deficiency (Partial thromboplastin antecedent)
• Factor X (Stuart-Power Factor) deficiency
• Factor V (Labile Factor) deficiency
• Factor II (Prothrombin) deficiency
• Factor I (Fibrinogen) deficiency
• Gaucher's disease
• Hemodialysis patients
• Hypofibrinogenemia
• Leukemia
• Liver disease (Severe)/Cirrhosis
• Lupus anticoagulant
• Malabsorption
• Polycythemia
• Renal disease
• Vitamin K deficiency
• von Willebrand's disease

Drugs that increase aPTT include:

• Therapeutic anticoagulants
• Heparin
• Hirudin
• Argatroban
• Other drugs such as:
• Anistreplase
• Antihistamines
• Ascorbic acid
• Chlorpromazine
• Salicylates

Critical Values:

• >70 seconds
• Important signs:
• Bleeding gums
• Blood in stool
• Hematoma at the puncture site
• Hemorrhage
• Prolonged bleeding
• Shock

• Administration of protamine sulfate can be used to reverse heparin and to some degree heparinoids or LMWH's

Low Result

The aPTT value may be decreased in the following conditions:

• Hypercoagulable states
• DIC
• Inadequate centrifugation

References

• Lab Tests Online®. aPTT: at a glance. [Homepage on the Internet]c2006. Last updated on Dec 27, 2004. Last accessed on July 06, 2006. Available at http://www.labtestsonline.org/understanding/analytes/aptt/glance.html
• Laboratory Corporation of America. Partial Thromboplastin Time (PTT), Activated. [Homepage on the Internet]c2003. Last updated on Feb 11, 2005. Last accessed on July 06, 2006. Available at http://www.labcorp.com/datasets/labcorp/html/chapter/mono/cg003300.htm
• Legnani C, Mattarozzi S, Cini M et al. Abnormally short activated partial thromboplastin time values are associated with increased risk of recurrence of venous thromboembolism after oral anticoagulation withdrawal. Br J Haematol 2006 Jul;134(2):227-232
• McGarry TF Jr, Gottileb RS, Morganroth J et al. The relationship of anticoagulation level and complications after successful percutaneous transluminal coronary angioplasty. Am Heart J. 1992 Jun;123(6):1445-51.
• Wiwanitkit V. Activated partial thromboplastin time abnormality in patients with cholangiocarcinoma.Clin Appl Thromb Hemostat. 2004; 10(1):69-71