Laboratory Evaluation of Hemostasis

Question 1

What is a normal platelet count?

Answer 1

Adults: 150,000-450,000/mm3. Peds: 150,000-350,000 /mm3

Question 2

When is a platelet count usually high?

Answer 2

Acute phase reaction. Early CML. Essential. thrombocytosis Polycythemia vera. Post splenectomy

Question 3

When is a platelet count usually low?

Answer 3

DIC. Hemolytic anemia. Hypersplenism. ITP. Leukemia. Prosthetic heart valve. Recent transfusion

Question 4

Describe bleeding time

Answer 4

A measurement of the time required for bleeding from a superficial puncture to stop (ie how well platelets interact with blood vessel walls to form blood clots). A screening test for platelet dysfunction. Useful in the diagnosis of Von Willebrand’s

Question 5

What is a normal bleeding time?

Answer 5

3-8 minutes

Question 6

Describe prothrombin time and its uses

Answer 6

Measures vitamin K dependent clotting ability, and extrinsic pathway. Used to screen for bleeding disorders and used to monitor patients on warfarin

Question 7

What are normal prothrombin time values?

Answer 7

Adults: 11-13 seconds. DVT prophylaxis (INR): 2-3. Mechanical valve and anti-phospholipid antibody syndrome (INR): 2.5-3.5

Question 8

Describe activated partial thromboplastin time (PTT) and its uses

Answer 8

measure of the time taken for a clot to form in citrated blood following the addition of calcium and a phospholipid platelet substitute.Measures effectiveness of the Intrinsic Pathway. Used to work up bleeding disorders and to monitor heparin therapy. Screen for lupus anticoagulant

Question 9

What are normal PTT values?

Answer 9

Adults: 25-35 secs. On anticoagulant therapy: 1.5-2.5 x the control value. Peds: Newborn: 31-54 secs. 1-6 yrs: 24-36 secs

Question 10

What tests should you do for the intrinsic and extrinsic coagulation pathways?

Answer 10

Intrinsic pathway: PTT, VIII, IX, XI, and XII. Extrinsic pathway: PT, II, V, VII

Question 11

What factors are vitamin-K dependent and are altered by warfarin?

Answer 11

factors VII, X, II (prothrombin)

Question 12

Describe thrombin time and its uses

Answer 12

The rate of conversion of fibrinogen to fibrin in the as measured by the addition of thrombin to citrated blood. Measure of fibrinolytic pathway

Question 13

What is a normal thrombin time?

Answer 13

15-20 secs