Medical Laboratory Science Review Harr. 2.2 Coagulation: Platelet and Vascular Disorders

B. Platelet aggregation and ATP release B Lumi-aggregation measures platelet aggregation and ATP release. It is performed on whole blood diluted with saline. Platelet aggregation is measured by impedance, whereas ATP release is measured by addition of luciferin to a blood sample. There is no ATP release in storage pool deficiencies.

Lumi-aggregation measures: A. Platelet aggregation only B. Platelet aggregation and ATP release C. Platelet adhesion D. Platelet glycoprotein Ib

B. Normal platelet aggregation to collagen, ADP, and epinephrine; decreased aggregation to ristocetin B Bernard-Soulier syndrome is a disorder of platelet adhesion caused by deficiency of glycoprotein Ib. Platelet aggregation is normal in response to collagen, ADP, and epinephrine but abnormal in response to ristocetin

When performing platelet aggregation studies, which set of platelet aggregation results would most likely be associated with Bernard-Soulier syndrome? A. Normal platelet aggregation to collagen, ADP, and ristocetin B. Normal platelet aggregation to collagen, ADP, and epinephrine; decreased aggregation to ristocetin C. Normal platelet aggregation to epinephrine and ristocetin; decreased aggregation to collagen and ADP D. Normal platelet aggregation to epinephrine, ristocetin, and collagen; decreased aggregation to ADP

C. Alpha granule defect C Gray's syndrome is a platelet granule defect associated with a decrease in alpha granules resulting in decreased production of alpha granule proteins such as platelet factor 4 and beta thromboglobulin. Alpha granule deficiency results in the appearance of agranular platelets when viewed on a Wright'sstained blood smear.

Which defect characterizes Gray's syndrome? A. Platelet adhesion defect B. Dense granule defect C. Alpha granule defect D. Coagulation defect

B. Cyclo-oxygenase B Aspirin prevents platelet aggregation by inhibiting the activity of the enzyme cyclo-oxygenase. This inhibition prevents the formation of thromboxane A2 (TXA2), which serves as a potent platelet aggregator.

Aspirin prevents platelet aggregation by inhibiting the action of which enzyme? A. Phospholipase B. Cyclo-oxygenase C. Tromboxane A2 synthetase D. Prostacyclin synthetase

C. Thrombocytopenia and giant platelets C Bernard-Soulier syndrome is associated with thrombocytopenia and giant platelets. It is a qualitative platelet disorder caused by the deficiency of glycoprotein Ib. In Bernard-Soulier syndrome, platelet aggregation to ADP is normal. Aggregation in the platelet function assay is abnormal. Factor VIII assay is not indicated for this diagnosis.

Bernard-Soulier syndrome is associated with: A. Decreased bleeding time B. Decreased factor VIII assay C. Thrombocytopenia and giant platelets D. Abnormal platelet aggregation to ADP

C. Escherichia coli 0157:H7 C HUS is caused by E. coli 0157:H7. It is associated with ingestion of E. coli contaminated foods and is commonly seen in children. The clinical manifestations in HUS are fever, diarrhea, thrombocytopenia, microangiopathic hemolytic anemia, and renal failure.

Hemolytic uremic syndrome (HUS) is associated with: A. Fever, thrombocytosis, anemia, and renal failure B. Fever, granulocytosis, and thrombocytosis C. Escherichia coli 0157:H7 D. Leukocytosis and thrombocytosis

D. Connective tissue D Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome) is a connective tissue disorder associated with telangiectases (dilated capillaries) of the mucous membranes and skin. Lesions may develop on the tongue, lips, palate, face, hands, nasal mucosa, and throughout the gastrointestinal tract. This disorder is an autosomal dominant condition that usually manifests in adolescence or early adulthood.

Hereditary hemorrhagic telangiectasia is a disorder of: A. Platelets B. Clotting proteins C. Fibrinolysis D. Connective tissue

B. TTP B TTP is characterized by neurological problems, fever, thrombocytopenia, microangiopathic hemolytic anemia, and renal failure.

Neurological findings may be commonly associated with which of the following disorders? A. HUS B. TTP C. ITP D. PTP

B. Glycoprotein Ib B Glycoprotein Ib is a platelet receptor for VWF. Glycoprotein Ib and VWF are both necessary for a normal platelet adhesion. Other proteins that play a role in platelet adhesion are glycoproteins V and IX.

Normal platelet adhesion depends upon: A. Fibrinogen B. Glycoprotein Ib C. Glycoprotein IIb, IIIa complex D. Calcium

C. Neonatal alloimmune thrombocytopenia C Neonatal alloimmune thrombocytopenia is similar to the hemolytic disease of the fetus and newborn. It results from immunization of the mother by fetal platelet antigens. The offending antibodies are commonly anti HPA-1a alloantibodies that are directed against glycoproteins IIb/IIIa, Ib/IX, Ia/IIb, and CD 109. The maternal antibodies cross the placenta, resulting in thrombocytopenia in the fetus.

Several hours after birth, a baby boy develops petechiae and purpura and a hemorrhagic diathesis. The platelet count is 18 × 109/L. What is the most likely explanation for the low platelet count? A. Drug-induced thrombocytopenia B. Secondary thrombocytopenia C. Neonatal alloimmune thrombocytopenia D. Neonatal DIC

C. Platelet granules C Storage pool deficiencies are defects of platelet granules. Most commonly, a decrease in platelet-dense granules is present with decreased release of ADP, ATP, calcium, and serotonin from platelet-dense granules.

Storage pool deficiencies are defects of: A. Platelet adhesion B. Platelet aggregation C. Platelet granules D. Platelet production

A. APTT is normal in TTP but prolonged in DIC A Thrombotic thrombocytopenic purpura is a platelet disorder in which platelet aggregation increases, resulting in thrombocytopenia. Schistocytes are present in TTP as a result of microangiopathic hemolytic anemia; however, the PT and APTT are both normal. In DIC, the PT and APTT are both prolonged, the platelet count is decreased, and schistocytes are seen in the peripheral smear.

TTP differs from DIC in that: A. APTT is normal in TTP but prolonged in DIC B. Schistocytes are not present in TTP but are present in DIC C. Platelet count is decreased in TTP but normal in DIC D. PT is prolonged in TTP but decreased in DIC

D. Clopidogrel (Plavix) D The VerifyNow P2Y12 test is used to assess a patient's response to antiplatelet drugs such as clopidogrel (Plavix) and prasugrel (Effient). These drugs are given orally for prevention of thrombosis along with aspirin, or as alternative antiplatelet drugs for patients who cannot tolerate or are not sensitive to aspirin. Clopidogrel and prasugrel prevent platelet aggregation by irreversibly binding to P2Y12, which is a platelet membrane receptor for ADP. The VerifyNow P2Y12 test is a whole blood test and uses ADP as an aggregating agent to measure the level of platelet aggregation impaired by these medications. The baseline platelet aggregation is established. The percent (%) change from baseline aggregation is calculated and reported as % P2Y12 inhibition

The P2Y12 ADP receptor agonist assay may be used to monitor platelet aggregation inhibition to which of the following drugs? A. Warfarin B. Heparin C. LMWH D. Clopidogrel (Plavix)

B. Hypersplenism B Hypersplenism is associated with thrombocytopenia. In this condition, up to 90% of platelets can be sequestered in the spleen, causing decreases in circulatory platelets. Postsplenectomy, acute blood loss, and increased proliferation of pluripotential stem cells are associated with thrombocytosis.

Thrombocytopenia may be associated with: A. Postsplenectomy B. Hypersplenism C. Acute blood loss D. Increased proliferation of pluripotential stem cells

B. Increased platelet aggregation B Thrombotic thrombocytopenic purpura (TTP) is a quantitative platelet disorder associated with increased intravascular platelet activation and aggregation resulting in thrombocytopenia. The PT and APTT results are normal in TTP.

Thrombotic thrombocytopenic purpura (TTP) is characterized by: A. Prolonged PT B. Increased platelet aggregation C. Thrombocytosis D. Prolonged APTT

Platelet aggregometer, VerifyNow, PFA-100 D. All of the above D All of the instruments listed can be used to evaluate platelet function. Platelet function testing is done to either determine the cause of bleeding in a patient with normal platelet count and normal coagulation tests, or to assess the efficacy of antiplatelet drugs.

Which of the following instruments can be used to evaluate platelet function? A. Platelet aggregometer B. VerifyNow C. PFA-100 D. All of the above

A. Spontaneous remission within a few weeks A Acute immune thrombocytopenic purpura is an immune-mediated disorder found predominantly in children. It is commonly associated with infection (primarily viral). It is characterized by abrupt onset, and spontaneous remission usually occurs within several weeks

Which of the following is a characteristic of acute immune thrombocytopenic purpura? A. Spontaneous remission within a few weeks B. Predominantly seen in adults C. Nonimmune platelet destruction D. Insidious onset

B. Immune-mediated thrombocytopenia/ alloantibodies B Post-transfusion purpura is a rare form of alloimmune thrombocytopenia characterized by severe thrombocytopenia following transfusion of blood or blood products. PTP is caused by antibody-related platelet destruction in previously immunized patients. In the majority of cases, the alloantibody produced is against platelet antigen A1 (PlA1), also referred to as HPA-1a.

Which of the following is associated with post-transfusion purpura (PTP)? A. Nonimmune thrombocytopenia/ alloantibodies B. Immune-mediated thrombocytopenia/ alloantibodies C. Immune-mediated thrombocytopenia/ autoantibodies D. Nonimmune-mediated thrombocytopenia/ autoantibodies

A. Autoimmune disease A Acquired TTP is an autoimmune disease associated with autoantibodies produced against VWF cleaving enzyme (ADAMTS-13). This deficiency results in an increase in plasma VWF and consequently increased platelet aggregation and thrombocytopenia

Which of the following is correct regarding acquired thrombotic thrombocytopenic purpura? A. Autoimmune disease B. Decreased VWF C. Decreased platelet aggregation D. Decreased platelet adhesion

B. Collagen B Collagen is the only commonly used agent that demonstrates a single-wave (monophasic) response preceded by a lag time.

Which of the following platelet aggregating agents demonstrates a monophasic aggregation curve when used in optimal concentration? A. Trombin B. Collagen C. Adenosine diphosphate (ADP) D. Epinephrine

C. Prostacyclin C Prostacyclin is released from the endothelium and is an inhibitor of platelet aggregation. Thromboxane A2 promotes platelet aggregation. Thromboxane B2 is an oxidized form of thromboxane A2 and is excreted in the urine. Antithrombin is a physiological anticoagulant.

Which of the following prevents platelet aggregation? A. Tromboxane A2 B. Tromboxane B2 C. Prostacyclin D. Antithrombin

C. Platelet count C Von Willebrand's disease is an inherited, qualitative platelet disorder resulting in increased bleeding, prolonged APTT, and decreased factor VIII:C and VWF levels. The platelet count and morphology are generally normal in von Willebrand's disease, but aggregation in the platelet function assay is abnormal.

Which of the following test results is normal in a patient with classic von Willebrand's disease? A. Bleeding time B. Activated partial thromboplastin time C. Platelet count D. Factor VIII:C and von Willebrand's factor (VWF) levels

C. Normal platelet aggregation to ristocetin; decreased aggregation to collagen, ADP, and epinephrine C Glanzmann's thrombasthenia is a disorder of platelet aggregation. Platelet aggregation is normal in response to ristocetin, but abnormal in response to collagen, ADP, and epinephrine

Which set of platelet responses would be most likely associated with Glanzmann's thrombasthenia? A. Normal platelet aggregation to ADP and ristocetin; decreased aggregation to collagen B. Normal platelet aggregation to collagen; decreased aggregation to ADP and ristocetin C. Normal platelet aggregation to ristocetin; decreased aggregation to collagen, ADP, and epinephrine D. Normal platelet aggregation to ADP; decreased aggregation to collagen and ristocetin