Ch. 26 Coagulation

Measures the time required to form a fibrin clot after activation of the Extrinsic pathway

• Heparin
• Measures the time required to form a fibrin clot after activation of the Intrinsic Pathway

• 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.

• 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

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

• 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

7,9,10,11,12

Incubate serum @37C for 24 hours 1,2,5,8 removed.

• 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

• Aspirin
• Platelet counts <100,000
• HCT < 30%
• Lipemia
• Uremia (renal failure)

80-150 seconds

60-100 seconds

• Operator dependancy
• Scarring
• Insensitivity to some plt. disorder
• Poor indicator of surgical bleeding

• 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

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

• vWD
• 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

Normal: 45-65%

• 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