APTT

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Details

The APTT test measures the time it takes for blood to clot via the intrinsic and common coagulation pathways

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APTT (Activated Partial Thromboplastin Time) - Comprehensive Medical Test Guide

Why is it done?
- Measures the intrinsic and common pathways of blood clotting cascade by evaluating clotting factor activity and function
- Evaluates time required for blood plasma to clot after specific activation reagents are added
- Screens for bleeding disorders and clotting factor deficiencies (Factors VIII, IX, XI, XII, and fibrinogen)
- Monitors anticoagulation therapy with heparin or warfarin
- Detects presence of inhibitors or anticoagulants (lupus anticoagulant, factor-specific inhibitors)
- Investigates unexplained bleeding or bruising
- Pre-operative assessment before surgery to evaluate bleeding risk
- Baseline testing before starting anticoagulant therapy or when transitioning between anticoagulants
Normal Range
- Reference Range: 30-40 seconds (may vary by laboratory and reagent used)
- Unit of Measurement: Seconds (sec)
- Normal Result Meaning: Blood clotting time is within expected range, indicating adequate clotting factors and normal intrinsic/common pathway function
- Prolonged (Elevated) APTT: >40 seconds - Blood takes longer than normal to clot, may indicate clotting factor deficiency, inhibitor presence, or anticoagulant effect
- Shortened (Low) APTT: <30 seconds - Blood clots faster than normal, may indicate increased clotting risk, hypercoagulability, or testing artifact
- Critical Values: Results >60 seconds usually prompt immediate laboratory and physician notification due to significant bleeding risk
- Therapeutic Range (on Heparin Therapy): Typically 1.5-2.5 times the normal baseline or 45-70 seconds depending on clinical situation
Interpretation
- Prolonged APTT Causes:
  - Clotting factor deficiencies (Factors VIII, IX, XI, XII, fibrinogen, prothrombin)
  - Heparin therapy (unfractionated or low-molecular-weight when on high doses)
  - Warfarin therapy (affects vitamin K-dependent factors)
  - Lupus anticoagulant (autoimmune inhibitor)
  - Factor-specific inhibitors (hemophilia with inhibitors)
  - Disseminated intravascular coagulation (DIC)
  - Severe liver disease affecting clotting factor synthesis
  - Vitamin K deficiency (affects factors II, VII, IX, X)
  - Fibrinogen abnormalities or severe hypofibrinogenemia
  - Specific inherited bleeding disorders (Hemophilia A and B, von Willebrand disease)
- Shortened APPT Causes:
  - Hypercoagulable states or thrombophilia conditions
  - Increased Factor VIII levels
  - Laboratory artifact or blood sample hemolysis
  - Early pregnancy or estrogen use
- Mixing Study Interpretation:
  - If APPT corrects with mixing study (patient plasma mixed with normal plasma) - suggests factor deficiency
  - If APPT remains prolonged after mixing - suggests presence of inhibitor or anticoagulant
- Factors Affecting Test Results:
  - Improper blood collection (insufficient blood or excess anticoagulant in collection tube)
  - Hemolysis, lipemia, or icterus in sample
  - Temperature variation during sample handling
  - Delayed sample processing or prolonged storage
  - Different laboratory reagents and analyzers producing slightly different values
  - Patient medications (aspirin, NSAIDs, antibiotics, steroids)
Associated Organs
- Primary Organs/Systems:
  - Hematologic system (blood and blood-forming organs)
  - Liver (primary site of most clotting factor synthesis)
  - Bone marrow (production of platelets and blood cells involved in clotting)
- Conditions Associated with Abnormal Results:
  - Hemophilia A (Factor VIII deficiency) and Hemophilia B (Factor IX deficiency)
  - Von Willebrand Disease
  - Liver disease and cirrhosis (impaired clotting factor synthesis)
  - Kidney disease (uremia affecting platelet function and Factor V)
  - Systemic Lupus Erythematosus (SLE) and antiphospholipid syndrome
  - Disseminated Intravascular Coagulation (DIC) from infections, malignancy, trauma
  - Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS)
  - Acute leukemia and other hematologic malignancies
  - Vitamin K deficiency and malabsorption syndromes
- Complications Associated with Abnormal Results:
  - Prolonged APPT complications: Spontaneous bleeding, hemorrhage (GI, intracranial, joint), excessive bleeding after surgery or trauma, internal bleeding
  - Shortened APPT complications: Venous thromboembolism (DVT, PE), arterial thrombosis, stroke, myocardial infarction, recurrent pregnancy loss
Follow-up Tests
- If APPT is Prolonged:
  - Mixing study (1:1 mix of patient and normal plasma) - differentiates factor deficiency from inhibitor
  - Prothrombin time (PT) - evaluates extrinsic pathway
  - Fibrinogen level - assesses fibrinogen adequacy
  - Platelet count - evaluates thrombocytopenia
  - Specific factor assays (Factor VIII, IX, XI, XII levels)
  - Lupus anticoagulant testing - if inhibitor suspected
  - Thrombin time (TT) - assesses fibrinogen function
  - Bleeding time - evaluates platelet function (if prolonged)
  - Von Willebrand factor antigen and activity testing
- If APPT is Shortened or Normal:
  - Thrombophilia testing if hypercoagulability suspected (Factor V Leiden, prothrombin mutation, antithrombin III, protein C/S)
  - Repeat APPT if artifact suspected
- For Therapeutic Monitoring:
  - Repeat APPT 24-48 hours after heparin initiation or dose change
  - Regular monitoring (every 24 hours for first few days, then daily or as needed) during heparin therapy
  - Baseline APPT before starting warfarin, then INR monitoring during warfarin therapy (APPT not used for warfarin monitoring)
  - APPT monitoring when switching from heparin to warfarin
- Related Coagulation Studies (Complementary Information):
  - Complete blood count (CBC) - platelet and hemoglobin levels
  - Liver function tests - assess hepatic synthetic function
  - Kidney function tests - evaluate renal contribution to coagulopathy
Fasting Required?
- Fasting Requirement: No
- Food/Fluid Restrictions: No fasting required; patient may eat and drink normally before test
- Medications: Continue all anticoagulant medications (heparin, warfarin, DOACs) as prescribed unless specifically instructed otherwise by physician
- Medications to Disclose: Inform laboratory of aspirin, NSAIDs, antibiotics, steroids, or any recent medication changes
- Patient Preparation:
  - No special preparation needed
  - Wear comfortable, loose-fitting clothing to facilitate blood draw
  - Inform phlebotomist of anxiety about needles or history of difficult blood draws
  - Ensure adequate hydration before test (drink water)
  - Report any recent bleeding episodes or bleeding tendency to healthcare provider before test
- Sample Collection Details:
  - Blood collected by venipuncture into a 3.2% sodium citrate tube (light blue-topped tube)
  - Tube must be filled to correct volume (typically 2.7 mL) to maintain proper blood-to-anticoagulant ratio
  - Sample must be inverted 3-4 times immediately after collection to mix anticoagulant
  - Sample must be kept at room temperature and processed within 1-2 hours of collection
  - Do not refrigerate or freeze sample before analysis

How our test process works!