Partial Thromboplastin Time

From Anvita Health Wiki

Contents 1 Reference-interval 2 Principle 3 Increases 4 Decreases 5 More General Terms 6 Additional Terms 7 References

Reference-interval

• normal range: < 35 seconds (method-dependent)
• therapeutic range for heparin therapy: 60-90 seconds

Principle

• Assessment of coagulation factors

• factor II
• factor V
• factor VIII
• factor IX
• factor X
• factor XI
• 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

• causes of increased PTT*

• 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

• decrease in plasma prekallikrein
• decrease in plasma high molecular weight kininogen
• plasma fibrinogen levels < 50 mg/dL or dysfibrinogenemia
• circulating anticoagulant: lupus anticoagulant
• drugs

• heparin
• chlorpromazine
• valproic acid

• failure for correct for hematocrit
• 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
  
• causes of increased PT & PTT: [3]

• factor II deficiency
• factor V deficiency
• factor X deficiency
• vitamin K deficiency (late)
• warfarin

Decreases

• compensated low-grade coagulopathy (activated coagulation system)
• traumatic venipuncture contaminating specimen with tissue thromboplastin

More General Terms

• clinical coagulation test

Additional Terms

• coagulation cascade
• prothrombin time (PT)

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

partial thromboplastin time (PTT)