Activated prothrombin time

Prothrombin time (PT) is a coagulation assay, which measures the time for plasma to clot upon activation by thromboplastin (a mixture of tissue factor and phospholipids). 

Administration of zafirlukast and aspirin increases plasma levels of zafirlukast, When zafirlukast is administered with warfarin, there is an increased effect of the anti coagulant. Administration of zafirlukast and theophylline or erythromycin may result in a decreased level of zafirlukast. Administration of montelukast with other drugs has not revealed any adverse responses. Administration of montelukast with aspirin and NSAIDs is avoided in patients with known aspirin sensitivity. Administration of zileuton with propranolol increases the activity or the propranolol with theophylline increases serum theophylline levels and with warfarin may increase prothrombin time (PT). A prothrombin blood test should be done regularly in the event dosages of warfarin need to be decreased. 

Table 32-3 summarizes laboratory results obtained on patients with three different causes of jaundice—hemolytic anemia (a prehepatic cause), hepatitis (a hepatic cause), and obstruction of the common bile duct (a posthepatic cause). Laboratory tests on blood (evaluation of the possibihty of a hemolytic anemia and measurement of prothrombin time) and on semm (eg, electrophoresis of proteins activities of the enzymes ALT, AST, and alkahne phosphatase) are also important in helping to distinguish between prehepatic, hepatic, and posthepatic causes of jaundice. 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Check complete blood count, prothrombin time, international normalization ratio, activated partial thromboplastin time, fibrinogen levels... 

Prothrombin time PT is performed by adding thromboplastin (tissue) factor and calcium to citrate-anticoagulated plasma, recalcifying the plasma, and measuring the clotting time. The major utility of PT is to measure the activity of the vitamin K-dependent factors II, VII, and X. The PT is used in evaluation of liver disease, to monitor warfarin anticoagulant effect, and to assess vitamin K deficiency. 

Preanalytical variables that affect global tests for coagulation such as prothrombin time (PT) and activated partial thromboplastin time (APTT) include the choice and concentration of anticoagulant, anticoagulant-to-blQod ratio, pH, concentration of divalent cations, hematocrit, and storage temperature, to mention a few. 

Ho C., Wu S. The influence of time, temperature, and packed cell volume on activated partial thromboplastin time and prothrombin time. Thromb Res 1991 62,625-33. 

Progressive liver damage (shock liver) manifests as elevated serum hepatic transaminases and unconjugated bilirubin. Impaired synthesis of clotting factors may increase prothrombin time (PT), international normalized ratio, and activated partial thromboplastin time (aPTT). 

Contraindications to heparin therapy include hypersensitivity to the drug, active bleeding, hemophilia, severe liver disease with elevated prothrombin time (PT), severe thrombocytopenia, malignant hypertension, and inability to meticulously supervise and monitor treatment. 

Routine liver assessment tests include alkaline phosphatase, bilirubin, aspartate transaminase, alanine transaminase, and y-glutamyl transpeptidase (GGT). Additional markers of hepatic synthetic activity include albumin and prothrombin time. The substances are typically elevated in chronic inflammatory liver diseases such as hepatitis C, but may be normal in others with resolved infectious processes. 

Baseline laboratory tests should include complete blood cell count, prothrombin time, activated partial thromboplastin time, liver and renal function tests, and serum carcinoembryonic antigen (CEA). Serum CEA can serve as a marker for monitoring colorectal cancer response to treatment, but it is too insensitive and nonspecific to be used as a screening test for early-stage colorectal cancer. 

Prothrombin time decrease. Hot water extract of the rhizome, administered intragastrically to mice for 1 month, was active. The extract was used in combination with 7 g Bupleurum falcatum, 5 g Pinellia ternata, 3 g Scutellaria baicalensis, 2 g Gly-cyrrhiza glabra, 1 g Zingiber officinale, 3 g Panax ginseng, and 3 g Zizyphus jujuba in 700 mL water ° . 

E. Therapeutic response Intravenous bivalirudin produces a rapid and dose-dependent prolongation of the activated partial thromboplastin time (aPTT), prothrombin time, activated clotting time (ACT), and thrombin time. 

Treatment with warfarin should be initiated with standard doses of 5-10 mg rather than the large loading doses formerly used. The initial adjustment of the prothrombin time takes about 1 week, which usually results in a maintenance dose of 5-7 mg/d. The prothrombin time (PT) should be increased to a level representing a reduction of prothrombin activity to 25%... 

Quantification of coagulation factors is notoriously difficult, because of the interrelations among the various components of the coagulation cascade, the broad range of normal values, and considerable inter-laboratory variability (52). This variability is illustrated by a WHO study of users of combined oral contraceptives, conducted on several continents, which showed statistically significant differences among clinical centers in prothrombin time, fibrin plate lysis, plasminogen, and activated partial thromboplastin time (SEDA-16, 464). Effects also vary between different populations, users of different doses, users of different products, and tests performed at different periods of the medication cycle (63,69). 

In 12 patients chronically maintained on warfarin, atorvastatin 80 mg/day for 2 weeks reduced mean prothrombin times slightly, but only for the first few days of the 2-week treatment period (35). Thus, atorvastatin had no consistent effect on the anticoagulant activity of warfarin and adjustments in warfarin doses should not be necessary. 

Note ACE = angiotensin-converting enzyme INR = international normalized ratio PT = prothrombin time PTT = partial thromboplastin time ECG = electrocardiogram PAF = platelet-activating factor AUC = area under the concentration/time curve. 

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