Activated partial thromboplastin time test

Accepting the above limitations of our knowledge of the true in vivo reaction sequence, a series of clot-endpoint tests has been used for many years to determine the hemostatic balance in any patient. The first, known as the thrombin time test, can be used to measure the concentration of fibrinogen (B15). The second assay, the activated partial thromboplastin time test (APTT), measures the components of the intrinsic pathway (M4). These include the serine proteases (Factors XII, XI, X, and II), the cofactors (Factors VIII and V) and again, fibrinogen. Most of the hereditary deficiencies... 

Before administering the first dose of heparin, the nurse obtains the patients vital signs. The most commonly used test to monitor heparin is activated partial thromboplastin time (APTT). Blood is drawn for laboratory studies before giving the first dose of heparin to obtain baseline data (See the discussion on preadministration assessment for the oral anticoagulants.)... 

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. 

Baseline complete blood count (CBC) and coagulation tests (activated partial thromboplastin time and International Normalized Ratio) should be obtained, as most patients will receive antithrombotic therapy, which increases the risk for bleeding. 

Liver function tests [international normalization ratio (INR), activated partial thromboplastin time (aPTT), and bilirubin] may be abnormal if disease has metastasized to the liver. 

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. 

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. 

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). 

The main cause of debate at present with regard to UFH centers on the amount used peri-PCI. The level of anticoagulation produced by UFH is measured by the activated partial thromboplastin time and activated clotting time (ACT), the latter being available in the cardiac catheter laboratory as a near-patient test. 

Treatment options are largely supportive. An assessment should first be made for airway patency and adequacy of breathing. Circulation may become affected as shock develops secondary to severe gastroenteritis. The following laboratory studies are recommended for all symptomatic patients computerized blood count, electrolytes, and coagulation studies (prothrobin time, activated partial thromboplastin time). In cases of uncertain or unknown exposure, there is an enzyme-linked immunosorption assay test available for the detection and verification of the presence of ricin... 

Several new compounds have been reported that affect the formation of a fibrin clot. Aromatic diamidines, such as, 21, were reported to inhibit several proteolytic enzymes including thrombin.74 Concanavalin A (a globulin protein from the jack bean) inhibits fibrin formation by inhibiting the lipoprotein cofactor in the production of thrombin and thus decreasing the rate of thrombin production.75 Several antibiotics (penicillins and cephalosporins) have been reported to affect fibrin clot formation as well as platelet function. Cephalothin (22) has been shown to delay fibrin polymerization and thus prolong the activated partial thromboplastin time (APTT) and thrombin time tests.78... 

Baseline laboratory tests should be obtained and include a complete blood cell (CBC) count, platelet count, prothrombin time, activated partial thromboplastin time, and liver and renal function tests. Abnormal liver function tests may suggest liver involvement with tumor. However, patients with metastatic disease to the liver may have normal liver function tests, and abnormal liver function tests are not always indicative of metastatic disease. 

Marlar, R.A., Cook, J., Johnston, M., Kitchen, S., Machlin, S., Shafer, D., and Worfolk, L. (2007). One stage prothrombin time (pt) test and activated partial thromboplastin time (APTT) test. Approved Guideline, 2nd edition, Vol. 28(20), Clinical Laboratory Standards Institute, HA47 A2. 

Anticoagulant Activity Assay. The anticoagulant activities of IV-acetylated heparin and all further derivatized heparins were determined based on activated partial thromboplastin time (APTT) assay methods (15). Bovine blood was collected in 3.8% sodium-citrated (9 parts blood to 1 part citrate solution) and centrifuged at 5000 x g for 15 min. The supernatant plasma was collected and pooled for subsequent APTT testing. Prior to testing plasma was kept refrigerated no longer than 6 h after... 

Mechanism and effects Regular heparin binds to and activates endogenous antithrombin 111 (ATlIl). The heparin-ATIll complex combines with and inactivates thrombin (activated factor 11) and several other factors, especially factor X. In the presence of heparin, antithrombin III inhibits the coagulation factors approximately 1000-fold faster than in its absence. Low doses of heparin also coat the endothelial walls of vessels and reduce the activation of clotting elements by these cells. Because it acts on preformed blood components, heparin is also active in vitro—almost instantaneously. The action of heparin is monitored with the activated partial thromboplastin time laboratory test (aPTT or PTT). 

The activated partial thromboplastin time (aPTT) is the second most common method for monitoring anticoagulant therapy, measuring all the clotting factors in the intrinsic pathway as opposed to the PT test, which measures the extrinsic pathway. 

Activated partial thromboplastin time (APTT) was determined using the Fibrometer method.(9) Sample sheet was incubated in 300 m1 of control plasma (Control Plasma N, Beohring Co., Germany) for 1 h afterward the plasma was separated. The partial thromboplastin (0.1 ml. Neothrombin) was preheated for 2 min and the obtained test plasma (0.1 ml, 37 C) as mentioned above was added, followed by the addition of 0.025M... 

X, ]X, VDI, W, V, and IE in plasma were determined by the degree of correction obtained when dilutions of the test h plasma were added to a severe single factor deficient plasma. The degree of correction was determined by the prothrombin time or activated partial thromboplastin time. Results were compared with the degree of correction obtained when normal plasma was added to the same severe factor deficient plasma. Normal plasma was considered to provide 100 % correction. 

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