Hema

• Hemostasis

  Maintenance of blood flow within the vascular system
• If the patient has many bruises or mentions a tendency to bleed, the phlebotomist should extend the time for observing the venipuncture site from 1 to 5 minutes and should apply a pressure bandage before dismissing the patient
• To observe any adverse reactions of the patient to the phlebotomy procedure
• Factors V and VIII

  Considered as labile factors (easily destroyed; easily deteriorate in plasma)
• Must use an anticoagulant that is able to preserve such factors
• Cold temperature (1 to 6oC) storage

  Causes precipitation of von Willebrand factor, activation of Factor VII, and destruction of platelets
• 0.105 to 0.109 M (3.2%) buffered Sodium Citrate


  Found in light blue top tubes
• Inversions


  1. 3-4x

  2. Inversion more than 4x = platelets become activated (shortened PT and aPTT)
• Ratio

  • 9:1 (blood to anticoagulant ratio)
  • May ↑ the stability of factors V and VIII (labile factors)

  
• CTAD (Citrate, Theophylline, Adenosine, Dipyridamole)

  • Less commonly used
  • Found in light blue top tubes
  • For PF4 (Platelet Factor IV assays) and β-TG (beta-thromboglobulin) assays
• Factors that may affect coagulation test results (PT and/or APTT)

  • Shortened test results:
  • Hemolysis
  • Excessive agitation
  • Prolonged tourniquet application
  • Excessive needle manipulation
  • Platelet contamination
  • Prolonged test results:
  • Presence of clots
  • Increased anticoagulant concentration
• Phlebotomist must provide tubes with relatively decreased anticoagulant volumes for collection of blood from a patient whose hematocrit is high

  
• There is NO evidence suggesting a need for increasing the volume of anticoagulant for specimens from patients with anemia, even when the hematocrit is < 20%
• Preferred Needles for Hemostasis Specimens

  • Adult with good veins, specimen < 25 mL: 20 or 21 gauge, thin-walled, 1.0 or 1.25 inches long
  • Adult with good veins, specimens > 25 mL: 19 gauge, 1.0 or 1.25 inches long
  • Child or adult with small, friable, or hardened veins: 23 gauge, winged-needle set; apply minimal negative pressure
  • Transfer of blood from syringe to tube: 19 gauge, slowly inject through tube closure
  • Syringe with winged-needle set: 20, 21, or 23 gauge, thin-walled; use only for small, friable, or hardened veins or specialized coagulation testing
• Hemostasis Specimen Storage Times and Temperatures

  • PT with no unfractionated heparin (UFH) in specimen: 18 to 24oC, 24 hours
  • PTT with no unfractionated heparin (UFH) in specimen: 4 hours
  • PTT for monitoring UFH therapy: Separate within 1 hour, test within 4 hours
  • PT when UFH is present in specimen
• Thrombosis


  Pathological formation of blood clots in veins or arteries that obstruct blood flow

  
• Antithrombotics


  • Drugs used to treat and prevent thrombosis
  • Include antiplatelets and anticoagulants
• Antiplatelets


  • Aspirin: inhibits COX (cyclooxygenase)
  • Clopidogrel and Prasugrel: bind platelet P2Y12 (ADP receptor)
  • Abciximab and Tirofiban: bind GP IIb/IIIa (fibrinogen receptor)
• Anticoagulants


  • Suppress coagulation
  • Examples: Warfarin (inhibits synthesis of factors II, VII, IX, and X; monitored by PT) and Heparin (accelerates binding of antithrombin to thrombin and factor Xa; monitored by APTT)
• Types of Bleeding


  • Petechiae (1mm; small pinpoint hemorrhages)
  • Purpura (3mm; generally round)
  • Ecchymosis a.k.a. bruise (>1 cm; generally irregular in shape)
  • Menorrhagia (Excessive menstrual bleeding)
  • Metrorrhagia (Irregular uterine bleeding not related to menstruation)
  • Hematohidrosis (Sweating of blood)
  • Epistaxis (Nosebleed)
  • Hematemesis (Vomiting of blood)
  • Hemoptysis (Expectoration of blood)
  • Hemarthrosis (Leakage of blood into the joint cavity)
  • Hematochezia (Passage of fresh blood in stools)
  • Melena (Passage of old blood in stools)
• Stages of Hemostasis


  • Primary Hemostasis (involves blood vessels and platelets)
  • Secondary Hemostasis (involves formation of fibrin meshwork through activated coagulation factors)
• Blood Vessels

  • 3 Coats (Tunics) Composing the Tissue in a Blood Vessel Wall:
  • Tunica Intima (Innermost layer; endothelium)
  • Tunica Media (Composed of smooth muscle and elastic fibers; thickest coat)
  • Tunica Adventitia (Outermost layer; composed of fibrous connective tissue)

  
• Types of Blood Vessels

  • Arteries (4 mm; distributing blood vessels that leave the heart)
  • Veins (5 mm; collecting blood vessels that return to the heart)
  • Capillaries (8 µm; blood passes from the arterial to the venous system)

  
• Substances Released from or Found on the Surface of Intact Endothelial Cells

  • Prostacyclin (Inhibits platelet activation)
  • Adenosine (Stimulates vasodilation)
  • Thrombomodulin (Binds thrombin and reduces its ability to participate in the clotting process)
  • Heparan Sulfate (Weakly enhances antithrombin)
  • TPA (Tissue Plasminogen Activator; major plasminogen activator)
  • VWF (Von Willebrand Factor; aids in platelet adhesion and acts as a carrier protein for factor VIII)
• ADAMTS 13


  VWF-cleaving protease; prevents thrombosis by regulating the size of circulating VWF
• Platelets


  • Arise from megakaryocytes in bone marrow
  • Important in both primary and secondary hemostasis
  • 3 Major Functions: Form platelet plug, Participate in plasma coagulation, Preserve endothelial lining

  
• Reticulated Platelets


  Newly released from megakaryocytes and still contain RNA; appear in compensation for thrombocytopenia

  
• They originated from the cytoplasm of megakaryocytes
• Platelets cluster with the RBCs near the center of the blood vessel

  
• Platelets move back and forth with the WBCs from venules into the white pulp of the spleen
• LIFE SPAN: 9-10 days
• Wright-stained PBS


  Platelets are spread throughout the RBC monolayer (normal: 7 to 21 cells per 100x [OIO] field)

  
• RBC monolayer


  The area in the PBS where RBCs are near each other but are not overlapping; where platelet count is done
• Platelet diameter


  Average diameter of 2.5 µm (or 2 to 4 µm)
• 3 MAJOR FUNCTIONS

  • To form an aggregate plug of platelets that can slow down or stop blood loss
  • To participate in plasma coagulation
  • To preserve the endothelial lining of the blood vessels

  
• Reticulated platelets

  • Aka: Stress platelets
  • Appear in compensation for thrombocytopenia
  • Newly released from megakaryocytes and still contain RNA
  • Markedly larger than the usual (mature) platelets (diameter in PBS: exceeds 6 µm [MPV reaches 12 to 14 fL])
• Clinical use of reticulated platelets

  • Can help differentiate bone marrow failure from peripheral destruction in thrombocytopenia
  • Early predictor of bone marrow recovery after chemotherapy and transplantation
• Reticulated platelets: potentially prothrombotic (maybe associated with increased risk of cardiovascular disease)
• Normal platelet diameter


  2.5 µm (average)
• Mean Platelet Volume (MPV)

  • Reference Range: 6.8 to 10.2 fL
  • Average volume of individual platelets in a specimen
  • EDTA causes swelling of platelets (causes approximately 20% increase in MPV during the first hour). After the first hour, the platelet size stabilizes and becomes normal again
  • Should be based on EDTA specimens that are between 1 to 4 hours' old