Medical Laboratory Science Review Harr. 2.1 Coagulation and Fibrinolytic Systems/Reagents and Methods

C. Thrombin time C Fibrinogen can be quantitatively measured by a modification of the thrombin time by diluting the plasma, because the thrombin clotting time of diluted plasma is inversely proportional to the concentration of fibrinogen (principle of Clauss method).

A modification of which procedure can be used to measure fibrinogen? A. PT B. APTT C. Thrombin time D. Fibrin degradation products

A. Factor I A Factor I (fibrinogen) is necessary for platelet aggregation along with the glycoprotein IIb/IIIa complex. Factor I is also a substrate in the common pathway of coagulation. Thrombin acts on fibrinogen to form fibrin clots.

A protein that plays a role in both coagulation and platelet aggregation is: A. Factor I B. Factor VIII C. Factor IX D. Factor XI

B. Reject the sample and request a new sample B A 4.5-mL blue-top tube contains 4.5 mL blood + 0.5 mL sodium citrate. The tube should be 90% full. A tube with 3.0 mL blood should be rejected as quantity not sufficient (QNS). QNS samples alter the necessary blood to an anticoagulant ratio of 9:1. The excess anticoagulant in a QNS sample binds to the reagent calcium, thereby resulting in prolongation of the PT and APTT.

A standard 4.5-mL blue-top tube filled with 3.0 mL of blood was submitted to the laboratory for PT and APTT tests. The sample is from a patient undergoing surgery the following morning for a tonsillectomy. Which of the following is the necessary course of action by the technologist? A. Run both tests in duplicate and report the average result B. Reject the sample and request a new sample C. Report the PT result D. Report the APTT result

B. Spontaneous activation of fibrinolysis B Primary fibrinolysis is a rare pathological condition in which a spontaneous systemic fibrinolysis occurs. Plasmin is formed in the absence of coagulation activation and clot formation. Primary fibrinolysis is associated with increased production of plasminogen and plasmin, decreased plasmin removal from the circulation, and spontaneous bleeding

In primary fibrinolysis, the fibrinolytic activity results in response to: A. Increased fibrin formation B. Spontaneous activation of fibrinolysis C. Increased fibrin monomers D. DIC

B. Thrombosis B Plasminogen deficiency is associated with thrombosis. Plasminogen is an important component of the fibrinolytic system. Plasminogen is activated to plasmin, which is necessary for degradation of fibrin clots to prevent thrombosis. When plasminogen isdeficient, plasmin is not formed, causing a defect in the clot lysing processes

Plasminogen deficiency is associated with: A. Bleeding B. Thrombosis C. Increased fibrinolysis D. Increased coagulation

B. Sodium citrate B The anticoagulant of choice for most coagulation procedures is sodium citrate (3.2%). Because factors V and VIII are more labile in sodium oxalate, heparin neutralizes thrombin, and EDTA inhibits thrombin's action on fibrinogen, these anticoagulants are not used for routine coagulation studies.

The anticoagulant of choice for most routine coagulation studies is: A. Sodium oxalate B. Sodium citrate C. Heparin D. Ethylenediaminetetraacetic acid (EDTA)

C. Thromboplastin and calcium C Thromboplastin and calcium (combined into a single reagent) replace the tissue thromboplastin and calcium necessary in vivo to activate factor VII to factor VIIa. This ultimately generates thrombin from prothrombin via the coagulation cascade.

What reagents are used in the PT test? A. Thromboplastin and sodium chloride B. Thromboplastin and potassium chloride C. Thromboplastin and calcium D. Actin and calcium chloride

A. p-nitroanaline A The chromogenic, or amidolytic, assays use a color-producing substance known as a chromophore. The chromophore used for the coagulation laboratory is p-nitroaniline (pNa). The pNa is bound to a synthetic oligopeptide substrate. The protease cleaves the chromogenic substrate at the site binding the oligopeptide to the pNA, which results in release of pNA. Free pNA has a yellow color; the color intensity of the solution is proportional to the protease activity and is measured by a photodetector at 405 nm

What substrate is used in a chromogenic factor assay? A. p-nitroanaline B. Chloropheonol red C. Prussian blue D. Ferricyanide

D. Factor XIII D Factor XIII is not measured by the PT or APTT. Factor XIII (fibrin stabilizing factor) is a transamidase. It creates covalent bonds between fibrin monomers formed during the coagulation process to produce a stable fibrin clot. In the absence of factor XIII, the hydrogen bonded fibrin polymers are soluble in 5M urea or in 1% monochloroacetic acid.

Which clotting factor is not measured by PT and APTT tests? A. Factor VIII B. Factor IX C. Factor V D. Factor XIII

B. PT and APTT B Patients with vitamin K deficiency exhibit decreased production of functional prothrombin proteins (factors II, VII, IX, and X). Decreased levels of these factors prolong both the PT and APTT.

Which coagulation test(s) would be abnormal in a vitamin K-deficient patient? A. PT only B. PT and APTT C. Fibrinogen level D. Thrombin time

D. Monoclonal against D-dimer D The D-dimer is the fibrin degradation product generated by the action of plasmin on cross-linked fibrin formed by XIIIa. The patient plasma is mixed with latex particles coated with monoclonal antibodies against D-domains. The test can be automated or performed manually on a glass slide, looking macroscopically for agglutination. ELISA methods are also available. Normal D-dimer in plasma is less than 2 ng/mL. Increased levels of D-dimer are associated with DIC, thrombolytic therapy, venous thrombosis, and thromboembolic disorders. The D-dimer assay has a 90% 95% negative predictive value, and has been used to rule out thrombosis and thromboembolic disorders.

Which of the following antibodies is used in the D-dimer assay? A. Polyclonal directed against X and Y fragments B. Polyclonal directed against D-dimer C. Monoclonal against D and E fragments D. Monoclonal against D-dimer

C. It is required for carboxylation of glutamate residues of some coagulation factors C Vitamin K is necessary for activation of vitamin K dependent clotting factors (II, VII, IX, and X). This activation is accomplished by carboxylation of glutamic acid residues of the inactive clotting factors. The activity of vitamin K is not enhanced by heparin therapy. Vitamin K is present in a variety of foods and is also the only vitamin made by the organisms living in the intestine.

Which of the following characterizes vitamin K? A. It is required for biological activity of fibrinolysis B. Its activity is enhanced by heparin therapy C. It is required for carboxylation of glutamate residues of some coagulation factors D. It is made by the endothelial cells

D. V, VIII D Factors V and VIII are activated by the thrombin that is generated by the action of TF-VIIa on factor X to form factor Xa. Factor Xa forms a complex with factor Va on the platelet surfaces. FXa -Va complex in the presence of phospholipid and Ca+2 transform more prothrombin to thrombin.

Which of the following clotting factors are activated by thrombin that is generated by tissue pathway (TF-VIIa)? A. XII, XI B. XII, I C. I, II D. V, VIII

C. XII, XI, IX, VIII, X, V, II, I C The APTT test evaluates the clotting factors in the intrinsic pathway (XII, XI, IX, and VIII) as well as the common pathway (X, V, II, and I).

Which of the following clotting factors are measured by the APTT test? A. II, VII, IX, X B. VII, X, V, II, I C. XII, XI, IX, VIII, X, V, II, I D. XII, VII, X, V, II, I

C. XIIa C Factor XIIa does not play a role in coagulation in vivo; however, in vitro, the deficiency of this factor causes a prolonged APTT result. In vitro, factor XII is activated by substances such as glass, Kaolin, and ellagic acid, and in vivo it may be activated by exposure to a negatively charged cell surface membrane such collagen as well as kallikrein (an activated form of prekallikrein) and high molecular weight kininogen (HMWK). In vivo, factor XIIa plays an important role in the fibrinolytic system by activating plasminogen to plasmin. Plasmin degrades the fibrin clot at the site of injury. Deficiency of factor XII is associated with thrombosis and not bleeding. Factors VIIa, Xa, and IIa play a role in vivo and in vitro.

Which of the following clotting factors plays a role in clot formation in vitro, but not in vivo?in vitro clot formation and not in vivo coagulation? A. VIIa B. IIa C. XIIa D. Xa

B. Tissue factor B In vivo, activation of coagulation occurs on the surface of activated platelets or cells that have tissue factor. Tissue factor is found on the surface of many cells outside the vascular system (extrinsic). Upon vascular injury, TF is exposed to the vascular system. TF has high affinity for factors VII and VIIa. TF activates factor VII to VIIa and forms TF-VIIa complex. TF-VIIa complex in the presence of Ca+2 and platelet phospholipid activates factors IX to IXa and X to Xa. Factor Xa forms a complex with cofactor Va (Xa-Va) on the surface of the activated platelets. Factor Xa-Va complex in the presence of Ca+2 and platelet phospholipid converts prothrombin (factor II) to thrombin (IIa). Thrombin acts on soluble plasma fibrinogen to form a fibrin clot, which is stabilized by activated factor XIII (XIIIa). In addition, activated factor IX (IXa) forms a complex with activated cofactor VIII (VIIIa) on the surface of the activated platelets. Factor IXa-VIIIa complex in the presence of Ca+2 and platelet phospholipid converts factor X to Xa with the end products of thrombin and fibrin clot as discussed previously. The classical description of intrinsic, extrinsic, and common pathways does not take place in vivo. The concept of these three pathways is used to explain clot formation in laboratory tests. The activated thromboplastin time (APTT) is determined by the intrinsic and common pathways, while the prothrombin time (PT) is determined by the extrinsic and common pathways. The extrinsic pathway is so named because the tissue factor is derived from extravascular cells.

Which of the following initiates in vivo coagulation by activation of factor VII? A. Protein C B. Tissue factor C. Plasmin activator D. Trombomodulin

B. It standardizes PT result B INR is used to standardize PT results to adjust for the difference in thromboplastin reagents made by different manufacturers and used by various institutions. The INR calculation uses the International Sensitivity Index (ISI) value, and is used to monitor an oral anticoagulant such as warfarin. INR is not used to standardize APTT testing.

Which of the following is correct regarding the international normalized ratio (INR)? A. It uses the International Sensitivity Ratio (ISR) B. It standardizes PT results C. It standardizes APTT results D. It is used to monitor heparin therapy

C. Tissue plasminogen activator C Tissue plasminogen activator (tPA) is an endogenous (produced in the body) activator of plasminogen. It is released from the endothelial cells by the action of protein C. It converts plasminogen to plasmin. Streptokinase is an exogenous (not made in the body) activator of plasminogen.

Which of the following is referred to as an endogenous activator of plasminogen? A. Streptokinase B. Transamidase C. Tissue plasminogen activator D. Tissue plasminogen activator inhibitor

D. Test has a negative predictive value D The D-dimer assay evaluates fibrin degradation. It is a nonspecific screening test that is increased in many conditions in which fibrinolysis is increased, such as DIC and fibrinolytic therapy. The D-dimer test is widely used to rule out thrombosis and thrombotic activities. The negative predictive value of a test is the probability that a person with a negative result is free of the disease the test is meant to detect. Therefore, a negative D dimer test rules out thrombosis and hence further laboratory investigations are not required.

Which of the following statements is correct regarding the D-dimer test? A. Levels are decreased in DIC B. Test detects polypeptides A and B C. Test detects fragments D and E D. Test has a negative predictive value

C. α2-Antiplasmin C α2-Antiplasmin is the main inhibitor of plasmin. It inhibits plasmin by forming a 1:1 stoichiometric complex with any free plasmin in the plasma and, therefore, prevents the binding of plasmin to fibrin and fibrinogen.

Which protein is the primary inhibitor of the fibrinolytic system? A. Protein C B. Protein S C. α2-Antiplasmin D. α2-Macroglobulin

C. 1:9 C The optimum ratio of anticoagulant to blood is one part anticoagulant to nine parts of blood. The anticoagulant supplied in this amount is sufficient to bind all the available calcium, thereby preventing clotting.

Which ratio of anticoagulant-to-blood is correct for coagulation procedures? A. 1:4 B. 1:5 C. 1:9 D. 1:10

A. Both prolonged A The volume of blood in a polycythemic patient contains so little plasma that excess anticoagulant remains and is available to bind to reagent calcium, thereby resulting in prolongation of the PT and APTT. For more accurate results, the plasma:anticoagulant ratio can be modified by decreasing the amount of anticoagulant in the collection tube using the following formula: (0.00185)(V)(100-H) = C, where V = blood volume in mL; H = patient's Hct; and C = volume (mL) of anticoagulant. A new sample should be drawn to rerun the PT and APTT.

Which results would be expected for the prothrombin time (PT) and activated partial thromboplastin time (APTT) in a patient with polycythemia? A. Both prolonged B. Both shortened C. Normal PT, prolonged APTT D. Both normal

D. It detects late degradation products (D and E) D The fibrin degradation product (FDP) test detects the late degradation products (fragments D and E) and not the early ones (fragments X and Y).

Which statement about the fibrinogen/fibrin degradation product test is correct? A. It detects early degradation products (X and Y) B. It is decreased in disseminated intravascular coagulation (DIC) C. It evaluates the coagulation system D. It detects late degradation products (D and E)

A. Stable for 24 hours if the sample is capped A According to Clinical Laboratory Standards Institute (CLSI, formerly NCCLS) guidelines, plasma samples for PT testing are stable for 24 hours at room temperature if capped. Refrigerating the sample causes cold activation of factor VII and, therefore, shortened PT results. The APTT samples are stable for 4 hours if stored at 4°C.

Which statement is correct regarding sample storage for the prothrombin time test? A. Stable for 24 hours if the sample is capped B. Stable for 24 hours if the sample is refrigerated at 4°C C. Stable for 4 hours if the sample is stored at 4°C D. Should be run within 8 hours

C. PT and APTT C Factor X is involved in the common pathway of the coagulation cascade; therefore, its deficiency prolongs both the PT and APTT. Activated factor X along with factor V in the presence of calcium and platelet factor III (PF3) converts prothrombin (factor II) to the active enzyme thrombin (factor IIa).

Which test would be abnormal in a patient with factor X deficiency? A. PT only B. APTT only C. PT and APTT D. Trombin time