2.1 Coagulation and Fibrinolytic Systems/Reagents and methods

Which statement is correct regarding sample storage for the PT 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

A According to CLSI guidelines, plasma samples for PT testing, if capped, are stable for 24 hours at RT. Refrigerating the sample causes cold activation of factor VII and, therefore shortening PT results. APTT results are stable 4 hours if stored at 4 C.

Which substrate is used in a chromogenic/amidolytic factor assay? A. p-nitroaniline (pNA) B. Chlorophenol Red C. Prussian Blue D. Ferricyanide

A Assay uses a color-producing substance known as chromophore. The chromophore used for th coagulation lab is pNa. Color intensity is proportional and is measured 405 nm.

A protein that plays a role in both coagulation and PLT aggregation is: a. Factor I b. Factor VIII c. Factor IX d. Factor XI

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

Which results would be expected for PT and APTT in a patient with polycythemia? a. both prolonged b. both shortened c. Normal PT, prolonged APTT d. Both Normal

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 a prolonged PT and APTT. You would have to ultimately add less anticoagulant to get accurate results.

The anticoagulant of choice for most routine coagulation studies is: a. Sodium oxalate b. sodium citrate c. heparin d. EDTA

B Factors V and VII 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.

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

B INR is used to standardize PT results to adjust for the differences in thromboplastin reagents. INR uses the international sensitivity index (ISI) value and is used to monitor oral anticoagulant, such as warfarin.

Which of the following initiates in vivo coagulation by activation of factor VII? a. Protein C b. Tissue Factor (TF) c. Plasmin Activator d. Thrombomodulin (TM)

B In vivo = inside TF is found on the surface of many cells outside the vascular system (extrinsic). On vascular injury, TF is exposed to the vascular system. TF has high affinity for factors VII and VIIa. With the presence of Calcium, the extrinsic PW can go on. TF is derived from extravascular cells.

Which coagulation test(s) would be abnormal in a patient with Vitamin K deficiency? a. PT only b. PT and APTT c. Fibrinogen level d. TT

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 PT and APTT.

Plasminogen deficiency is associated with: a. Bleeding b. thrombosis c. increased fibrinolysis d. increased coagulation

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 the degradation if fibrin clots to prevent thrombosis. When plasminogen is deficient, plasmin is not formed, causing a defect in the clot lysing process.

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 Primary fibrinolysis is a rare pathological condition in which 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.

A standard 4.5 mL blue top tube is 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 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 The tube should be 90% full. A tube with 3.0 mL of blood should be rejected because the quantity is not sufficient (QNS). The excess anticoagulant in a QNS sample binds to the reagent calcium, resulting in prolongation of PT and APTT.

Which protein is the primary inhibitor of the fibrinolytic system? a. Protein C b. Protein S c. A2-antiplasmin d. A2-macroglobulin

C A2-antiplasmin is the main inhibitor of plasmin. It inhibits plasmin by forming a complex with any free plasmin in plasma and thus, prevents binding of plasmin to fibrin and fibrinogen.

Which test would be abnormal in a patient with factor X deficiency? a. PT only b. APTT only c. PT and APTT d. Thrombin Time (TT)

C Factor X is involved in the common pathway; therefore, its deficiency prolongs both PT and APTT.

Which of the following clotting factors plays a role in clot formation in vitro, but not in vivo? a. Factor VIIa b. Factor IIa c. Factor XIIa d. Factor Xa

C Factor XIIa does not play a role in vivo, however in vitro the deficiency of this factor causes prolonged APPTs (Intrinsic). In vivo, factor XIIa plays an important role in the fibrinolytic system by activating plasminogen to plasmin. Plasmin then degrades fibrin clot at the site of injury.

A modification of which procedure can be used to measure fibrinogen? a. PT b. APTT c. TT d. Fibrin degradation products

C Fibrinogen can be quantitively measured by modification of the TT by diluting the plasma because the thrombin clotting time of diluted plasma is inversely proportional to the concentration of fibrinogen. (Clauss method)

Which of the following clotting factors are measured by the APTT test? a. Factors II, VII, IX, and X b. Factors VII, X, V, II, I c. Factors XII, XI, IX, VIII, X, V, II, I d. Factors XII, VII, X, V, II, I

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

Which anticoagulant to blood ratio is correct for coagulation procedures? a. 1:4 b. 1:5 c. 1:9 d. 1:10

C The optimal anticoagulant to blood ratio is one part anticoagulant to 9 parts blood. the anticoagulant binds to calcium, thereby preventing clotting.

Which reagents are used in the PT Test? a. Thromboplastin and sodium citrate b. Thromboplastin and potassium chloride c. Thromboplastin and calcium d. Actin and Calcium cloride

C Thromboplastin and Calcium are combined in a single reagent which replaces tissue thromboplastin and calcium in vivo to than activate factor VII to factor VIIa. Ultimately generates thrombin from prothrombin.

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 endothelial cells

C Vitamin K is necessary for activation of vitamin K dependent clotting factors (II, VII, IX, and X).

Which of the following is referred to as an endogenous activator of plasminogen? a. Streptokinase b. Transamidase c. Tissue plasminogen activator (tPA) d. tPA inhibitor

C 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 fragments of fibrin clot degradation are measured by the D-dimer test? a. Fragments X and Y b. Fibrinopeptide A and B c. Fragments D and E d. The D-D domains

D D dimer is a specific product resulting from digestion of cross-linked fibrin only. It consists of two D domains called D-D fragment and is a marker for thrombosis and fibrinolysis. The D-dimer test is used to diagnose acute and chronic DIC and to rule out thromboembolic disorders.

Which clotting factor is NOT measured by the PT and APTT tests? a. Factor VIII b. Factor IX c. Factor V d. Factor XIII

D Factor XIII is not measurable via PT and APTT. Factor XIII (fibrin stabilizing factor) helps produce a stable fibrin clot. In the absence of factor XIII, the hydrogen bonded fibrin polymers are unstable and therefore, soluble in 5M urea.

Which of the following clotting factors are activated by thrombin that is generated by tissue pathway (TF-VIIa)? A. Factors XII, XI B. Factors XII, I C. Factors I, II D. Factors 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 PLT surfaces. Factor Xa-Va complex is the presence of phospholipid and Ca 2+ transform more prothrombin to thrombin.

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

D The D-Dimer assay evaluates fibrin degradation. It is a nonspecifically screening test that shows increased values in many conditions in which fibrinolysis is increased such as DIC and fibrinolytic therapy. The negative predictive value of a test is the probability that a person with a negative result is free of the disease that the test was meant to detect. Therefore, a negative D-dimer test result rules out thrombosis, and further lab investigations are not required.

Which of the following antibodies is used in the D-Dimer assay? A. Polyclonal antibody directed against X and Y fragments B. Polyclonal antibody directed against D-dimer C. Monoclonal antibody against D and E fragments D. Monoclonal antibody 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. Patient plasma is mixed with a monoclonal Ab against the D-domains. Increased (>2 ng/ml) levels are associated with DIC, thrombolytic therapy, venous thrombosis, and thromboembolic disorders.