HEMOSTASIS

• Platelet adhesion to collagen occurs through glycoproteins on platelets that bind to collagen receptors on vascular walls.
• Von Willebrand factor (vWF) is produced by endothelial cells and megakaryocytes.
• The liver is the main site of synthesis of clotting factors II, V, VII, IX, X, XI, XII, protein C, antithrombin III, fibrinogen, plasminogen, and von Willebrand factor.
• The process of platelet activation is triggered by exposure to collagen, thrombin, and other factors released during tissue injury.
• Platelet activation leads to the release of granules containing factors that promote clot formation.
• Platelet activation is a crucial step in hemostasis that involves changes in the shape and adhesive properties of platelets.
• Kallikrein activates factor XI, leading to the formation of an enzyme complex that cleaves fibrinogen into fibrin monomers.
• The coagulation cascade is initiated by the activation of factor XII, which converts prekallikrein to kallikrein.
• Prolong tourniquet application will lead to false shortened clot-based result
• POLYCYTHEMIA or patient with ≥55% hematocrit will cause falsely prolonged results for clot-based coagulation tests
• Remedy for falsely prolonged results for clot-based coagulation tests for POLYCYTHEMIA or patients with ≥55% hematocrit

  Reduce the anticoagulant volume
• Hemostasis specimen stored at refrigerator temperature (1° C to 6° C)

  • Activates factor VII and XI
  • Destroys platelet activity through uncontrolled activation
  • Causes cryoprecipitation of large VWF multimers
• Endpoint methods for coagulation test:

  • Electromechanical
  • Photo-optical (turbidimetric)
  • Chromogenic / amidolytic
  • Immunologic
  • Nephelometric
  • Viscoelastic
• Hemostasis specimen storage:

  • PT: 18 – 24 'C, 24 Hours
  • PTT: 18 – 24 'C, 4 Hours
  • Factor assays: 18 – 24 'C, 4 hours
  • In household freezer: -20 'C, 2 weeks
  • Storage for 6 months: -70 'C, 6 months
• A coagulation test that measures a change in conductivity between two metal electrodes in plasma?

  Electromechanical
• Instrument that read at a fixed wavelength between 500 nm and 600 nm and it is the most commonly used system in today's clinical instruments

  Photo-optical (turbidometric) coagulometers
• This method employs a synthetic oligopeptide substrate conjugated to a chromophore, usually para-nitroaniline (pNA). Its analysis is a means for measuring specific coagulation factor activity because it exploits the factor's enzymatic (protease) properties

  Chromogenic or Amidolytic
• This assay is the newest assay available for routine coagulation testing. This assay is based on antigen-antibody reactions. This assay uses light absorbance

  Immunologic assay
• It is a modification of photo-optical end-point detection in which 90-degree or forward-angle light scatter, rather than OD, is measured. A light-emitting diode produces incident light at approximately 600 nm, and a photodetector detects variations in light scatter at 90 degrees (side scatter) and 180 degrees (forward-angle scatter). As fibrin polymers form, side scatter and forward-angle scatter rise. The timer stops when scatter reaches a predetermined intensity, and the interval is recorded.

  Nephelometry
• This assay uses thromboelastography. The assay provides information on the entire kinetic process of whole blood clot formation. It uses citrated whole blood.

  Viscoelastic
• Capabilities to alert the operator when preset criteria or errors have been exceeded for instrument performance and specimen quality.

  Flagging
• It is the automatic ordering of tests based on preset parameters or the results of prior tests

  Reflex testing
• Hemostasis specimen collection errors that require collection of new sample:

  • Short draw
  • Clotted specimen
  • Hemolysis
  • Lipemia or icterus
  • Prolonged tourniquet application
  • Specimen storage at 1-6'C
  • Specimen storage more than 25'C
• Hemostasis/coagulation specimens that are short draw, clotted, or hemolyzed are rejected
• Categorization of clotting factors:

  • According to pathway: Intrinsic, Extrinsic, Common
  • According to Characteristics or properties: Fibrinogen group, Prothrombin group, Contact group
  • According to Coagulation Test: PT, PTT, TCT, RT, ST, Duckert's
• What are the intrinsic factors?

  XII, XI, IX, VIII
• What are the extrinsic factors?

  III, VII
• What are the common factors?

  XIII, X, V, II, I
• A shift in the curve because of a change in pH (or hydrogen ion concentration)

  Bohr effect
• According to dilutional effect, the degree of thrombocytopenia is DIRECTLY PROPORTIONAL to the number of units transfused
• It can detect a change in plasma optical density (OD, light transmittance) during clotting. Light of a specified wavelength passes through plasma, and its intensity (OD) is recorded by a photodetector.

  Photo-optical (turbidimetric) coagulometers
• Chromogenic or Amidolytic types:

  • Direct -OD is proportional to the activity of the substance being measured
  • Indirect -the change in OD is inversely proportional to the concentration or activity of the substance being measured
• What factors belong to the fibrinogen group?

  I, V, VIII, XIII
• This group is consumed during coagulation. It is absent in serum. It is not absorbed by barium sulfate or aluminum hydroxide.

  Fibrinogen group
• This group increases in inflammation, pregnancy, stress and fear, and oral contraceptives.

  Fibrinogen group
• This is the largest group associated with coagulation

  Fibrinogen
• These groups are not consumed during coagulation. They are absorbed by barium sulfate or aluminum hydroxide.

  Prothrombin group and Contact group
• What factors belong to the prothrombin group?

  II, VII, IX, X
• What factors belong to the CONTACT group?

  XI, XII, PREKALLIKREIN, HMWK
• This group is Vitamin K dependent

  Prothrombin group