Partial thromboplastin time: Difference between revisions
m cleanup using AWB |
Added reference to potential value of shortened PTT values. While it might not be considered relevant clinically (yet), it is probably good to mention it. |
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==Interpretation== |
==Interpretation== |
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The typical reference range is between 25 [[second]]s and 39 s (depending on laboratory). Shortening of the PTT |
The typical reference range is between 25 [[second]]s and 39 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 thromboembolisms<ref>{{cite journal |author=Wolfgang Korte, MD, Susan Clarke, MT(ASCP), and Jerry B. Lefkowitz, MD |title=Short Activated Partial Thromboplastin Times Are Related |
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to Increased Thrombin Generation and an Increased Risk for Thromboembolism |journal=Am J Clin Pathol. |issue=113 |pages=123-127 |year=2000}}</ref>. 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: |
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* use of [[heparin]] (or contamination of the sample) |
* use of [[heparin]] (or contamination of the sample) |
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* [[antiphospholipid antibody]] (especially [[lupus anticoagulant]], which paradoxically increases propensity to [[thrombosis]]) |
* [[antiphospholipid antibody]] (especially [[lupus anticoagulant]], which paradoxically increases propensity to [[thrombosis]]) |
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Revision as of 16:29, 19 January 2012
| Partial thromboplastin time | |
|---|---|
| MeSH | D010314 |
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
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
The typical reference range is between 25 seconds and 39 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 thromboembolisms[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:
- use of heparin (or contamination of the sample)
- antiphospholipid antibody (especially lupus anticoagulant, which paradoxically increases propensity to thrombosis)
- coagulation factor deficiency (e.g. hemophilia)
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 correct 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.
History
The aPTT was first described in 1953 by researchers at the University of North Carolina at Chapel Hill.[4]
See also
- Prothrombin time (PT)
References
- ^ "MedlinePlus Medical Encyclopedia: Partial thromboplastin time (PTT)". Retrieved 2009-01-01.
- ^ "KCCT - General Practice Notebook". GP Notebook. Oxbridge Solutions Ltd. Retrieved 2010-06-08.
- ^ Wolfgang Korte, MD, Susan Clarke, MT(ASCP), and Jerry B. Lefkowitz, MD (2000). "Short Activated Partial Thromboplastin Times Are Related
to Increased Thrombin Generation and an Increased Risk for Thromboembolism". Am J Clin Pathol. (113): 123–127.
{{cite journal}}: line feed character in|title=at position 57 (help)CS1 maint: multiple names: authors list (link) - ^ 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.
{{cite journal}}: CS1 maint: multiple names: authors list (link)