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== Descripción ==
 
Este ensayo mide la eficacia de las vías «intrínseca» y «común» de la [[coagulación]]. La vía intrínseca ―conocida actualmente como «vía de activación por contacto»― implica al factor IX y cofactores; mientras que la vía común implica a los factores X y II, y cofactores. Este ensayo está enfocado en un paso específico del proceso de coagulación.
 
Además de ser utilizada para detectar anormalidades en la coagulación de la sangre,<ref name="urlMedlinePlus Medical Encyclopedia: Partial thromboplastin time (PTT)">{{cita web|url= http://www.nlm.nih.gov/medlineplus/ency/article/003653.htm|título=MedlinePlus Medical Encyclopedia: Partial thromboplastin time (PTT)|fechaacceso=1 de enero de 2009}}</ref> se utiliza también para monitorear los efectos terapéuticos del tratamiento con [[heparina]], un [[anticoagulante]] mayor. Se utiliza en conjunción con el ensayo de [[tiempo de protrombina]] (TP), el cual es capaz de medir la vía extrínseca de coagulación, la cual implica a los factores&nbsp;VII y [[factor tisular|tisular]].
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==Method Método ==
 
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 [[blood plasma|plasma]]
[[celite]], [[kaolin]], [[ellagic acid]]), and [[calcium]] (to reverse the anticoagulant effect of the oxalate) are mixed into the [[blood plasma|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.
 
== Interpretación ==
==Interpretation==
 
The typical reference range is between 30 [[second]]s 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.<ref name="pmid10631865">{{cite journal|last=Korte|first=Wolfgang|coauthors=Clarke, Susan; Lefkowitz, Jerry B.|title=Short activated partial thromboplastin times are related to increased thrombin generation and an increased risk for thromboembolism|journal=American journal of clinical pathology|date=2000 Jan|volume=113|issue=1|pages=123–7|pmid=10631865|doi=10.1309/G98J-ANA9-RMNC-XLYU}}</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:
* use of [[heparin]] (or contamination of the sample).
 
To distinguish the above causes, [[mixing test]]s 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 [[factor VIII|factors VIII]], [[factor IX|IX]], [[factor XI|XI]] and [[factor XII|XII]] and rarely [[von Willebrand factor]] (if causing a low factor VIII level) may lead to a prolonged aPTT correcting on mixing studies.
 
{{Bleeding worksheet}}
 
==History==
 
The aPTT was first described in 1953 by researchers at the [[University of North Carolina at Chapel Hill]].<ref>{{cite journal |author=Langdell RD, Wagner RH, Brinkhous KM |title=Effect of antihemophilic factor on one-stage clotting tests; a presumptive test for hemophilia and a simple one-stage antihemophilic factor assy procedure |journal=J. Lab. Clin. Med. |volume=41 |issue=4 |pages=637–47 |year=1953 |pmid=13045017 |doi=}}</ref>
 
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== Historia ==
TheLa aPTT wasse firstdescribió described inen 1953 bypor researchersinvestigadores atde thela [[UniversityUniversidad of Northde Carolina atdel Norte en Chapel Hill]].<ref>{{cite journal |author=Langdell RD, Wagner RH, Brinkhous KM |title=Effect of antihemophilic factor on one-stage clotting tests; a presumptive test for hemophilia and a simple one-stage antihemophilic factor assy procedure |journal=J. Lab. Clin. Med. |volume=41 |issue=4 |pages=637–47 |year=1953 |pmid=13045017 |doi=}}</ref>
 
== Realización del examen ==
 
== Interpretación ==
Los valores por debajo de 20 segundos[[segundo|s]] o por encima de 40 s (dependiendo de los rangos locales de referencia) generalmente se consideran anormales. Un tiempo de aPTT corto tiene poca relevancia clínica. Un tiempo prolongado de aPTT puede indicar:
 
Los valores por debajo de 20 segundos o por encima de 40 s (dependiendo de los rangos locales de referencia) generalmente se consideran anormales. Un tiempo de aPTT corto tiene poca relevancia clínica. Un tiempo prolongado de aPTT puede indicar:
* uso de [[heparina]] (o contaminación de la muestra);
* presencia de un [[anticuerpo]] antifosfolípidos (sobre todo en el [[lupus anticoagulante]], una afección que paradójicamente aumenta la propensión a la [[trombosis]]);
== Referencias ==
{{listaref}}
[[Categoría:AnálisisExámenes de sangre]]
 
[[Categoría:Análisis de sangre]]
[[Categoría:Signos clínicos]]
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