Platelet Count and Prothrombin Time Quiz

Platelet Count

• Normal range: 150,000–450,000/μL
• Thrombocythemia (abnormal platelet count) can have various causes. These include:
  • Splenectomy
  • Rheumatoid arthritis
  • Polycythemia vera
• Decreased platelet levels (thrombocytopenia) can be caused by:
  • Hypersplenism
  • Hemorrhage
  • Leukemia
  • DIC (Disseminated Intravascular Coagulation)

Prothrombin Time (PT)

• Normal range: 10–14 seconds
• Used to assess the extrinsic and common pathways of the clotting mechanism
• More sensitive to deficiencies in Vitamin K-dependent liver factors (II, VII, IX, and X)
• Increased levels (prolonged PT) suggest:
  • Liver disease
  • Vitamin K deficiency
  • Disseminated intravascular coagulation (DIC)
  • Hereditary factor deficiency

International Normalized Ratio (INR)

• Normal range: 0.8–1.1
• Standardizes PT results, as different thromboplastin sources can produce varying results.
• Calculated using the equation: INR = (patient PT/mean normal PT)ISI
• The ISI (International Sensitivity Index) reflects the sensitivity of the thromboplastin reagent compared to the World Health Organization standard.
• INR of 2.5–3.5 is considered normal during warfarin therapy

Activated Partial Thromboplastin Time (aPTT)

• Normal range: 30–40 seconds (PTT: 60–70 seconds)
• Used to identify deficiencies or inhibitors in the intrinsic pathway (factors VIII, IX, XI, and XII), and the final common pathway (factors II, V, and X).
• Patients on anticoagulant therapy have an aPTT of 1.5-2.5 times the control value in seconds.
• Increased levels indicate:
  • Congenital clotting factor deficiencies (like von Willebrand disease or hemophilia)
  • Cirrhosis of the liver
  • Vitamin K deficiency
  • Heparin administration

D-Dimer

• Normal range: <0.5 mcg/mL (<3 nmol/L)
• Patients on anticoagulants have a D-dimer level of 1.5 -2.5 x control value in seconds
• Marker of thrombotic activity; a fibrin degradation fragment produced during the lysis of cross-linked fibrin.
• Increased levels suggest:
  • Disseminated intravascular coagulation (DIC)
  • Deep Vein Thrombosis (DVT)
  • Pulmonary Embolism (PE)
  • Arterial thromboembolism
  • During thrombolytic or defibrinating therapy