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PT (10-13 seconds)
Measures the time required to form a fibrin clot after activation of the Extrinsic pathway
PTT (20-35 seconds)
Partial Thromboplastin Time
- Measures the time required to form a fibrin clot after activation of the Intrinsic Pathway
Fibrinogen (200-400 mg/dl)
- If low fibrinogen, time will be high.
- If high fibrinogen, time will be low.
- The time required for the clot to form is inversely proportional to the fibrinogen concentration.
Fibrin Degradation Products
- Fibrinolytic activity of plasma breaks fibrinogen and fibrin into smaller fragments called fibrin degradation products (Fibrin split products)
- When patient serum containing FDPs is added to latex particles coated with antibodies, these antibodies cross react with the FDPs to produce visible agglutination.
- Positive FDPs are associated with increased fibrinolysis (DIC, PE, DVT)
- FDP does not differentiate between primary fibrinolysis and Secondary because it uses an anti-fibrinogen antibody that reacts with FDPs and fibrinogen.
- Specific type (FDP)
- Plasmin degrades fibrin into smaller D,E,X,Y fragments.
- More specific for Secondary fibrinolysis becaust the D-dimer is formed from the degradation of cross-linked fibrin.
- Useful to diagnose DIC associated with 20
- D-dimer latex particles coated with anti-d dimer antibody
Mixing Studies (PT/PTT)
Results return/approach the normal range
The normal plasma will "correct" the patient plasma and the PT/PTT test will return to within the normal range.
Results do not approach the normal range
Elevated PT/PTT test can be caused by:
- A factor deficiency or a circulating anticoagulant (antibody directed against a coagulation factor also known as an inhibitor)
- Differentiate between these two, the abnormal patient plasma is mixed with an equal volume of normal plasma and the PT and/or PTT test is repeated with the patient plasma-normal plasma mixture.
The normal plasma is also inhibited and the PT/PTT test will remain elevated
- Screening tests such as the PT and PTT are increased, it is often necessary to ID the specific factor deficiency
- Different types of plasma or serum can be added to patient plasma to test for a correction of the PT or PTT tests
1,5, 8, 11,12
- Plasma mixed with barium sulfate or aluminum hydroxide and centrifuged
- Group II removed
Incubate serum @37C for 24 hours 1,2,5,8 removed.
Replaced bleeding time
- Sodium citrate whole blood aspirated through a small tube.
- DO NOT centrifuge prior to testing
- 2 types of apertures used (Collagen and Epinephrine; Collagen and ADP)
- Platelet activation and aggregation will clog the aperature and stop the flow of blood.
- Time required to stop blood flow is the closure time (reflects qualitative plt. function)
If the CEPI is elevated then CADP is performed
Causes of elevated closure time
- Platelet counts <100,000
- HCT < 30%
- Uremia (renal failure)
Bleeding time test isn't performed anymore because:
- Operator dependancy
- Insensitivity to some plt. disorder
- Poor indicator of surgical bleeding
Factor Assay 50-150%
(V, VII, VIII, IX, XI)
- Specific factor assays can determine the activity of specific coagulation proteins.
- Activity expressed as a % of normal
- Patient plasma is mixed with a known factor deficient plasma
- It's ability (or inability) to correct a known factor deficiency plasma determines how much of the factor the patient possesses.
Correct=Normal PTT or PT result
Bleeding Time Test (IVY)
Measurement of platelet function
As the cut injures the sub-endothelial lining of the capillaries, platelets adhere and aggregate at the injury, forming a platelet plug stopping the bleeding
Bleeding Time increased in:
- Bernard-Soulier Syndrome
- Glanzmann's thrombosthenia
- Platelet storage pool disease
- Aspirin ingestion
- Decreased platelet count <100,000
- Severely decreased fibrinogen concentrations
- Function of platelet function and the platelet count.
- If platelet decreased in number or function clot retraction is decreased.
- Increased fibrinolysis will also decrease clot retraction because the clot is dissolved as fast as retraction can occur.
- Normal clot retraction begins within 1 hour and complete by 24 hours
< 20 seconds
- Converts fibrinogen to fibrin monomers and into fibrin
- Time required for clot formation increased by: Decreased Fibrinogen concentration, Inhibitors (antibodies), Increased immunoglobulin concentrations, Heparin, FDP