Testing of Secondary Hemostasis Flashcards
Prothrombin time or protime (PT)
Performed by adding tissue thromboplastin to pt’s plasma.
PT is a screen for
Inherited or acquired deficiencies in the extrinsic and common pathways.
PT measures Factors
I, II, V, VII, and X
PT reference range
10-13 sec
PT procedure
Specimen and reagents must be prewarmed to 37 Celsius.
Pt plasma added to thromboplastin reagent (contains calcium)
PT monitors oral anticoagulant therapy
Coumadin and Warfarin
INR: International normalized ratio
Used to correct for differences in coagulation instruments, reagents, etc.
INR is a calculation and is reported with ALL PT results.
PT sources of error
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
Activated Partial Thromboplastin Time (APTT)
Performed by adding plt phospholipid substitute and contact activator (APTT reagent) and calcium to activate factor XII.
APTT is a screen for
Intrinsic and common pathways
APTT measures all factors except
VII (extrinsic pathway) and XIII
APTT reference range
28-35 sec
APTT procedure
Reagents and specimens pre-warmed
pt plasma added to phospholipid activator and then CaCl2 is added.
APTT monitors IV/injection anticoagulant therapt
Heparin
APTT sources of error
Same as PT
Activated Clotting Time (ACT)
Used to monitor the effectiveness of high dose heparin therapy.
ACT reference range
70-180 sec
Thrombin Clotting Time (TCT) (TT)
Measures clotting time of the last step of the coagulation cascade, which is the conversion of fibrinogen into fibrin by thrombin.
TCT is a test of which pathway?
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.
TCT Procedure
prewarm reagents and plasma, add pt plasma to thromin
TCT reference range
10-16 sec
*Can be falsely prolonged due to heparin.
Reptilase Time
Clotting similar to thrombin time except snake venom is used instead of thrombin.
Reptilase Time reference range
18-22 sec
*NOT prolonged by heparin
Fibrinogen Assay
Recommended test for estimating fibrinogen level.
Thrombin reagent is 25x more concentrated than in TCT.
Pt’s plasma is diluted.
Fibrinogen Assay reference range
200-400 mg/dL
Decreased fibrinogen
Liver disease, DIC
Increased fibrinogen
Inflammatory disease, pregnancy
APTT: Normal
PT: Abnormal
- Factor deficiency in extrinsic pathway (probably VII)
2. Specific factor inhibitor
APTT: Abnormal
PT: Normal
- Factor deficiency in intrinsic pathway (XII, XI, kallikrein, IX, or VIII)
- Specific factor inhibitor
- Lupus anticoagulant
APTT: Abnormal
PT: Abnormal
TCT: Normal
- Factor deficiency in common pathway
- Vitamin K deficiency
- Liver disease (multiple factor abnormalities)
- Inhibitor present
APTT: Abnormal
PT: Abnormal
TCT: Abnormal
- Factor deficiency (I-fibrinogen)
- Severe liver disease
- DIC
- Inhibitor
Mixing Study
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.
Mixing Study Procedure Part I
- pt plasma mixed with normal plasma
- APTT or PT performed
- If normal (corrected) then factor deficiency is suspected. If not normal, suspect inhibitor
Mixing Study Procedure Part II
- Since some inhibitors react slowly you must prewarm the abnormal pt plasma and normal plasma for 2 hours at 37.
- Rerun APTT and PT on warmed plasma dilution
- If APTT still normal (corrected) it is probably caused by a factor deficiency.
* Now you must perform specific factor assays.
Immediate PT and APTT after Mixing Study: Correction
2 hour incubation PT and APTT: Correction
Factor Deficiency
Immediate PT and APTT after Mixing Study: No Correction
2 hour incubation PT and APTT: No Correction
Lupus-like anticoagulant
Immediate PT and APTT after Mixing Study: Correction
2 hour incubation PT and APTT: NO Correction
Specific Inhibitor (Factor VIII)
Factor Assay
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.
Factor Assay ranges
Normal: 50-100%
Symptoms are evident at activity levels of 30% or less.
