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partial thromboplastin time (PTT)

Indications: - assessment of coagulation disorders - monitoring therapy with unfractionated heparin Contraindications: - anti-factor Xa heparin assay indicated a) patients with lupus anticoagulant b) patients also taking warfarin c) patients refractory to heparin (> 40,000 units/day) d) baseline elevated aPTT [7] Reference values: - normal range: < 35 seconds (method-dependent) - 25-35 seconds [5] - therapeutic range for heparin therapy: 60-90 seconds Principle: Assessment of coagulation factors 1) factor II 2) factor V 3) factor VIII 4) factor IX 5) factor X 6) factor XI 7) factor XII The assay is performed by activating contact factors with kaolin, ellagic acid or celite, adding a standardized phospholipid preparation as a platelet substitute & measuring the time to clot formation after adding excess Ca+2 to citrated plasma. Increases: 1) causes of increased PTT* a) decreases in coagulation factors < 30-40% of normal* - factor II deficiency - factor V deficiency - factor VIII deficiency - factor IX deficiency - factor X deficiency - factor XI deficiency - factor XII deficiency b) decrease in plasma prekallikrein c) decrease in plasma high molecular weight kininogen d) plasma fibrinogen levels < 50 mg/dL or dysfibrinogenemia e) circulating anticoagulant: lupus anticoagulant f) drugs - heparin - chlorpromazine - valproic acid g) failure for correct for hematocrit n) insufficient filling of vacutainer * ONLY factor VIII deficiency or factor IX deficiency associated with frequent or severe bleeding [3] Plasma mixing studies are performed to assess whether increased PTT is due to deficiency vs inhibitor 2) causes of increased PTT with normal PT [5] a) factor V deficiency b) factor IX deficiency c) factor XI deficiency d) factor XII deficiency e) von Willebrand's disease (severe) & factor VIII low f) heparin exposure 3) causes of increased PT & PTT: [3] a) factor II deficiency b) factor V deficiency c) factor X deficiency d) vitamin K deficiency (late) e) warfarin Decreases: 1) compensated low-grade coagulopathy (activated coagulation system) 2) traumatic venipuncture contaminating specimen with tissue thromboplastin Differential diagnosis: - prolonged prothrombin time, normal aPTT [5] - factor VII deficiency - disseminated intravascular coagulation (DIC) - liver disease - vitamin K deficiency - warfarin - normal prothrombin time, prolonged aPTT [5] - factor VIII deficiency - acquired factor VIII inhibitor - severely prolonged aPTT, NOT corrected with addition of normal plasma - factor IX deficiency - factor XI deficiency - factor XII deficiency - von Willebrand's disease (if factor VIII low) - lesser increases in aPTT - heparin - prolonged prothrombin time, prolonged aPTT [5] - factor V deficiency - factor X deficiency - factor II deficiency - fibrinogen deficiency - severe liver disease - disseminated intravascular coagulation (DIC) - vitamin K deficiency - warfarin toxicity - heparin overdose - normal prothrombin time, normal aPTT [5] - platelet dysfunction (acquired or congenital) - von Willebrand's disease (factor VIII not too low) - scurvy - Ehlers-Danlos syndrome - hereditary hemorrhagic telangiectasia - factor XIII deficiency

Related

coagulation cascade plasma mixing studies prothrombin time (PT)

General

clinical coagulation test

References

  1. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 726
  2. Guide to Clinical Laboratory Tests, 3rd ed, NW Teitz (ed) WB Saunders, 1995
  3. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 322
  4. Panel of 6 tests Laboratory Test Directory ARUP: 30133 - Panel of 4 tests Laboratory Test Directory ARUP: 30177 - Panel of 12 tests Laboratory Test Directory ARUP: 30181 - Partial Thromboplastin Time Laboratory Test Directory ARUP: 30235 - Panel of 16 tests Laboratory Test Directory ARUP: 30268 - Panel of 16 tests Laboratory Test Directory ARUP: 2003222 - Panel of 7 tests Laboratory Test Directory ARUP: 2003417 - Panel of 7 tests Laboratory Test Directory ARUP: 2003947
  5. Medical Knowledge Self Assessment Program (MKSAP) 17, 18. American College of Physicians, Philadelphia 2015. 2018.
  6. Tcherniantchouk O, Laposata M, Marques MB. The isolated prolonged PTT. Am J Hematol. 2013 Jan;88(1):82-5. Epub 2012 Jul 18. PMID: 22811044 Free Article
  7. NEJM Knowledge+ Hematology - Guervil DJ, Rosenberg AF, Winterstein AG et al Activated partial thromboplastin time versus antifactor Xa heparin assay in monitoring unfractionated heparin by continuous intravenous infusion. Ann Pharmacother. 2011 Jul;45(7-8):861-8 PMID: 21712506

Component-of

coagulation screening panel DIC panel PT/aPTT/fibrinogen in plasma