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PROLONGED THROMBIN TIME 1. When using the tilt tube hand method, tubes are tipped only until the clotting time is

60 seconds. Why? Because only very low fbrinogen or excess heparin cause theclotting times to be greater than 60 seconds.

. !he !hrombin !ime test is prolonged when the fbrinogen level is less than 100 mg"dl#hypofbrinogenema$. %t is also prolonged in the presence o& large 'uantities o&fbrinogen degradation products #()*s$ or excess heparin.

+. )ysfbrinogenemia #abnormal fbrinogen$ or afbrinogenemia #absence o& fbrinogen$

may cause a prolonged thrombin time. *athologic antithrombins may also prolong thethrombin time.

. -imply put/(ibrinogens less than 100 mg"dl will prolong a thrombin time greater than 60

seconds, since the endpoint is a fbrinogen clot./-ince very low fbrinogens are rare, when a thrombin time is greater than 60

seconds, it is presumed to be due to heparin.

SHORTENED THROMBIN TIME 1. !he !hrombin !ime is only shortened in the presence o& )extrans, which are plasma

expanders used in the operating room.

THROMBIN TIME (TT) TEST 

1. !he thrombin !ime test is per&ormed by mixing prewarmed thrombin solution #usuallybovine thrombin$ with prewarmed plasma at + degrees and obtaining the clottingtime in seconds. !he thrombin reagent cleaves fbrinogen, &orming fbrin polymers#which are observed as a clot$.

. )i2erent proportions o& thrombin solution and plasma can be used, but using 0. mleach ma3es end points easy to detect.

+. )epending on the thrombin concentration used, 4normal values4 may vary widely. !hus, a very low concentration o& thrombin might give a 4normal value4 o& +0 seconds,and a very high thrombin concentration a 4normal value4 or or + seconds.

ADJUSTING THE THROMBIN CONCENTRATION 1. 5 common practice, however, is to adust the thrombin concentration to give a clotting

time o& 17.0 8 or 9 1.0 second with pooled normal plasma.. With this system, the thrombin concentration is low enough that the test is very

sensitive to the presence o& low concentrations o& heparin.

PRACTICE QUESTIONS 1. !he !hrombin !ime test only measures the conversion o& fbrinogen to a fbrin clot a&ter

the addition o& excess thrombin to undiluted plasma./!rue

: !he !hrombin !ime test only measures the conversion o& fbrinogen to afbrin clot a&ter the addition o& excess thrombin to undiluted plasma . %tdoes not rely on any o& the clotting &actors located above fbrinogen in theplasma coagulation scheme.

. !he !hrombin !ime test is prolonged

5. When the fbrinogen level is less than 100 mg"dlB. %n the presence o& fbrinogen degradation products #()*s$ or heparin. )ue to dysfbrinogenemia or afbrinogenemia). %n the presence o& )extrans

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/!he correct answers are 5, B, and .: !he !hrombin !ime test is prolonged when the fbrinogen level is less than

100 mg"dl #hypofbrinogenema$.: %t is also prolonged in the presence o& large 'uantities o& fbrinogen

degradation products #()*s$ or excess heparin. )ysfbrinogenemia#abnormal fbrinogen$ or afbrinogenemia #absence o& fbrinogen$ maycause a prolonged thrombin time.

: *athologic antithrombins may also prolong the thrombin time.+. )epending on the thrombin concentration used, 4normal values4 may vary widely.

/!rue: )epending on the thrombin concentration used, 4normal values4 may vary

widely. !hus, a very low concentration o& thrombin might give a 4normalvalue4 o& +0 seconds , and a very high thrombin concentration a 4normalvalue4 or or + seconds.

SUMMARY  1. !he !hrombin !ime test is one o& three tests #along with the *rothrombin !ime test and

the 5ctivated *artial !hromboplastin !ime test$ done as part o& the screening &orabnormalities in the plasma coagulation system.

. !he !hrombin !ime test only measures the conversion o& fbrinogen to a fbrin clot a&terthe addition o& excess thrombin to undiluted plasma. %t does not rely on any o& the

clotting &actors located above fbrinogen in the plasma coagulation scheme.+. !he !hrombin !ime test is per&ormed by mixing prewarmed thrombin solution #usually

bovine thrombin$ with prewarmed plasma at + degrees and obtaining the clottingtime in seconds. !he thrombin reagent cleaves fbrinogen, &orming fbrin polymers.

. )i2erent proportions o& thrombin solution and plasma can be used, but using 0. mleach ma3es end points easy to detect.

7. )epending on the thrombin concentration used, 4normal values4 may vary widely. !hus, a very low concentration o& thrombin might give a 4normal value4 o& +0 seconds,and a very high thrombin concentration a 4normal value4 or or + seconds.

6. !he !hrombin !ime test is prolonged when the fbrinogen level is less than 100 mg"dl#hypofbrinogenema$. %t is also prolonged in the presence o& large 'uantities o&fbrinogen degradation products #()*s$ or excess heparin. )ysfbrinogenemia

#abnormal fbrinogen$ or afbrinogenemia #absence o& fbrinogen$ may cause aprolonged thrombin time. *athologic antithrombins may also prolong the thrombintime.

PRINCIPLE 1. *lasma is clotted by the addition o& bovine or porcine thrombin which has been

adusted to give a clotting time o& 1916 seconds with normal plasma.. !he thrombin time measures the conversion o& fbrinogen to fbrin polymer.