Testing of Secondary Hemostasis

Question 1

Prothrombin time or protime (PT)

Answer 1

Performed by adding tissue thromboplastin to pt’s plasma.

Question 2

PT is a screen for

Answer 2

Inherited or acquired deficiencies in the extrinsic and common pathways.

Question 3

PT measures Factors

Answer 3

I, II, V, VII, and X

Question 4

PT reference range

Answer 4

10-13 sec

Question 5

PT procedure

Answer 5

Specimen and reagents must be prewarmed to 37 Celsius.

Pt plasma added to thromboplastin reagent (contains calcium)

Question 6

PT monitors oral anticoagulant therapy

Answer 6

Coumadin and Warfarin

Question 7

INR: International normalized ratio

Answer 7

Used to correct for differences in coagulation instruments, reagents, etc.
INR is a calculation and is reported with ALL PT results.

Question 8

PT sources of error

Answer 8

Blood Collection: TF in sample and premature activation of factor VII.
Sample Processing: Delay in testing which may decrease factor V.
Pt HCT: Increased hct=decreased plasma volume
*Plasma to anticoagulant ratio: 5:1

Question 9

Activated Partial Thromboplastin Time (APTT)

Answer 9

Performed by adding plt phospholipid substitute and contact activator (APTT reagent) and calcium to activate factor XII.

Question 10

APTT is a screen for

Answer 10

Intrinsic and common pathways

Question 11

APTT measures all factors except

Answer 11

VII (extrinsic pathway) and XIII

Question 12

APTT reference range

Answer 12

28-35 sec

Question 13

APTT procedure

Answer 13

Reagents and specimens pre-warmed

pt plasma added to phospholipid activator and then CaCl2 is added.

Question 14

APTT monitors IV/injection anticoagulant therapt

Answer 14

Heparin

Question 15

APTT sources of error

Answer 15

Same as PT

Question 16

Activated Clotting Time (ACT)

Answer 16

Used to monitor the effectiveness of high dose heparin therapy.

Question 17

ACT reference range

Answer 17

70-180 sec

Question 18

Thrombin Clotting Time (TCT) (TT)

Answer 18

Measures clotting time of the last step of the coagulation cascade, which is the conversion of fibrinogen into fibrin by thrombin.

Question 19

TCT is a test of which pathway?

Answer 19

The common pathway specifically fibrinogen.

• Not commonly used to monitor anticoagulants.
• Used to detect dysfibrinogenemia which is associated with hereditary factor deficiency, DIC, and liver disease.

Question 20

TCT Procedure

Answer 20

prewarm reagents and plasma, add pt plasma to thromin

Question 21

TCT reference range

Answer 21

10-16 sec

*Can be falsely prolonged due to heparin.

Question 22

Reptilase Time

Answer 22

Clotting similar to thrombin time except snake venom is used instead of thrombin.

Question 23

Reptilase Time reference range

Answer 23

18-22 sec

*NOT prolonged by heparin

Question 24

Fibrinogen Assay

Answer 24

Recommended test for estimating fibrinogen level.
Thrombin reagent is 25x more concentrated than in TCT.
Pt’s plasma is diluted.

Question 25

Fibrinogen Assay reference range

Answer 25

200-400 mg/dL

Question 26

Decreased fibrinogen

Answer 26

Liver disease, DIC

Question 27

Increased fibrinogen

Answer 27

Inflammatory disease, pregnancy

Question 28

APTT: Normal PT: Abnormal

Answer 28

1. Factor deficiency in extrinsic pathway (probably VII) | 2. Specific factor inhibitor

Question 29

APTT: Abnormal PT: Normal

Answer 29

1. Factor deficiency in intrinsic pathway (XII, XI, kallikrein, IX, or VIII) 2. Specific factor inhibitor 3. Lupus anticoagulant

Question 30

APTT: Abnormal PT: Abnormal TCT: Normal

Answer 30

1. Factor deficiency in common pathway 2. Vitamin K deficiency 3. Liver disease (multiple factor abnormalities) 4. Inhibitor present

Question 31

APTT: Abnormal PT: Abnormal TCT: Abnormal

Answer 31

1. Factor deficiency (I-fibrinogen) 2. Severe liver disease 3. DIC 4. Inhibitor

Question 32

Mixing Study

Answer 32

If PT and/or APTT is prolonged, mixing studies are performed to differentiate factor deficiency from the presence of a circulating inhibitor. *This procedure will correct the prolonged PT or APTT if it is caused by a deficiency of one or more of the coagulation factors.

Question 33

Mixing Study Procedure Part I

Answer 33

1. pt plasma mixed with normal plasma 2. APTT or PT performed 3. If normal (corrected) then factor deficiency is suspected. If not normal, suspect inhibitor

Question 34

Mixing Study Procedure Part II

Answer 34

4. Since some inhibitors react slowly you must prewarm the abnormal pt plasma and normal plasma for 2 hours at 37. 5. Rerun APTT and PT on warmed plasma dilution 6. If APTT still normal (corrected) it is probably caused by a factor deficiency. * Now you must perform specific factor assays.

Question 35

Immediate PT and APTT after Mixing Study: Correction | 2 hour incubation PT and APTT: Correction

Answer 35

Factor Deficiency

Question 36

Immediate PT and APTT after Mixing Study: No Correction | 2 hour incubation PT and APTT: No Correction

Answer 36

Lupus-like anticoagulant

Question 37

Immediate PT and APTT after Mixing Study: Correction | 2 hour incubation PT and APTT: NO Correction

Answer 37

Specific Inhibitor (Factor VIII)

Question 38

Factor Assay

Answer 38

Performed to confirm a specific factor deficiency and to determine the actual activity of that factor within the plasma. *Basis of a factor assay is the ability of the pts plasma to correct a prolonged PT or APTT of a known factor deficient plasma.

Question 39

Factor Assay ranges

Answer 39

Normal: 50-100% | Symptoms are evident at activity levels of 30% or less.