Partial thromboplastin time

From Wikipedia, the free encyclopedia - View original article

Partial thromboplastin time
Intervention
Coagulation diagram.png
MeSHD010314
 
Jump to: navigation, search
"KccT" redirects here. For the radio station, see KCCT.
Partial thromboplastin time
Intervention
Coagulation diagram.png
MeSHD010314

The partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT or APTT) is a performance indicator measuring the efficacy of both the "intrinsic" (now referred to as the contact activation pathway) and the common coagulation pathways. Apart from detecting abnormalities in blood clotting,[1] it is also used to monitor the treatment effects with heparin, a major anticoagulant. It is used in conjunction with the prothrombin time (PT) which measures the extrinsic pathway. Kaolin cephalin clotting time (KccT) is a historic name for the activated partial thromboplastin time.[2]

Method[edit]

Blood samples are collected in tubes with oxalate or citrate to arrest coagulation by binding calcium. The specimen is then delivered to the laboratory. In order to activate the intrinsic pathway, phospholipid, an activator (such as silica, celite, kaolin, ellagic acid), and calcium (to reverse the anticoagulant effect of the oxalate) are mixed into the plasma sample. The time is measured until a thrombus (clot) forms. This testing is performed by a medical technologist.

The test is termed "partial" due to the absence of tissue factor from the reaction mixture.

Interpretation[edit]

The typical reference range is between 30 seconds and 50 s (depending on laboratory). Shortening of the PTT is considered to have little clinical relevance, but some research indicates that it might increase risk of thromboembolism.[3] Normal PTT times require the presence of the following coagulation factors: I, II, V, VIII, IX, X, XI, & XII. Notably, deficiencies in factors VII or XIII will not be detected with the PTT test. Prolonged APTT may indicate:

To distinguish the above causes, mixing tests are performed, in which the patient's plasma is mixed (initially at a 50:50 dilution) with normal plasma. If the abnormality does not disappear, the sample is said to contain an "inhibitor" (either heparin, antiphospholipid antibodies or coagulation factor specific inhibitors), while if it does occur a factor deficiency is more likely. Deficiencies of factors VIII, IX, XI and XII and rarely von Willebrand factor (if causing a low factor VIII level) may lead to a prolonged aPTT correcting on mixing studies.

Laboratory findings in various platelet and coagulation disorders (V - T)
ConditionProthrombin timePartial thromboplastin timeBleeding timePlatelet count
Vitamin K deficiency or warfarinProlongedNormal or mildly prolongedUnaffectedUnaffected
Disseminated intravascular coagulationProlongedProlongedProlongedDecreased
Von Willebrand diseaseUnaffectedProlonged or unaffectedProlongedUnaffected
HemophiliaUnaffectedProlongedUnaffectedUnaffected
AspirinUnaffectedUnaffectedProlongedUnaffected
ThrombocytopeniaUnaffectedUnaffectedProlongedDecreased
Liver failure, earlyProlongedUnaffectedUnaffectedUnaffected
Liver failure, end-stageProlongedProlongedProlongedDecreased
UremiaUnaffectedUnaffectedProlongedUnaffected
Congenital afibrinogenemiaProlongedProlongedProlongedUnaffected
Factor V deficiencyProlongedProlongedUnaffectedUnaffected
Factor X deficiency as seen in amyloid purpuraProlongedProlongedUnaffectedUnaffected
Glanzmann's thrombastheniaUnaffectedUnaffectedProlongedUnaffected
Bernard-Soulier syndromeUnaffectedUnaffectedProlongedDecreased or unaffected
Factor XII deficiencyUnaffectedProlongedUnaffectedUnaffected
C1INH deficiencyUnaffectedShortenedUnaffectedUnaffected

History[edit]

The aPTT was first described in 1953 by researchers at the University of North Carolina at Chapel Hill.[4]

References[edit]

  1. ^ "MedlinePlus Medical Encyclopedia: Partial thromboplastin time (PTT)". Retrieved 2009-01-01. 
  2. ^ "KCCT - General Practice Notebook". GP Notebook. Oxbridge Solutions Ltd. Retrieved 2010-06-08. 
  3. ^ Korte, Wolfgang; Clarke, Susan; Lefkowitz, Jerry B. (January 2000). "Short activated partial thromboplastin times are related to increased thrombin generation and an increased risk for thromboembolism". American journal of clinical pathology 113 (1): 123–7. doi:10.1309/G98J-ANA9-RMNC-XLYU. PMID 10631865. 
  4. ^ Langdell RD, Wagner RH, Brinkhous KM (1953). "Effect of antihemophilic factor on one-stage clotting tests; a presumptive test for hemophilia and a simple one-stage antihemophilic factor assy procedure". J. Lab. Clin. Med. 41 (4): 637–47. PMID 13045017.