Laboratory Values: Coagulation Studies

Coagulation studies assess the blood's ability to clot and are essential for monitoring anticoagulant therapy. Understanding these values is critical for preventing both bleeding and clotting complications. The NCLEX tests coagulation concepts extensively.

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The Coagulation Cascade

Blood clotting occurs through two pathways that converge:

Memory Aid:

• "PT/Pro-time = Warfarin = Extrinsic Pathway"
• "PTT = Pro-Thrombin Time = Heparin"

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Prothrombin Time (PT) and INR

PT (Prothrombin Time)

Normal Range: 11-13 seconds

PT measures the extrinsic pathway and is used to monitor Warfarin therapy. However, PT values vary between laboratories, making comparison difficult.

INR (International Normalized Ratio)

Normal Range: 0.8-1.1

The INR standardizes PT results across laboratories and is the preferred measure for monitoring Warfarin therapy.

Warfarin (Coumadin) Key Points

Mechanism: Inhibits Vitamin K-dependent clotting factors (II, VII, IX, X)

Onset: 3-5 days (delayed effect)

Duration: Long-lasting (takes days to reverse)

Monitoring:

• INR checked regularly (initially daily, then weekly, then monthly)
• Goal: Maintain within therapeutic range

Patient Education:

• Consistent Vitamin K intake (don't suddenly increase or decrease green leafy vegetables)
• Avoid NSAIDs (increase bleeding risk)
• Report signs of bleeding
• Wear medical alert identification

Elevated INR (> 3.0 for most conditions)

Signs of Over-Anticoagulation:

• Bruising
• Bleeding gums
• Nosebleeds
• Blood in urine or stool
• Prolonged bleeding from cuts

Nursing Interventions:

• Hold Warfarin
• Notify provider
• Administer Vitamin K (antidote) as ordered
• For severe bleeding: Fresh Frozen Plasma (FFP), Prothrombin Complex Concentrate (PCC)

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aPTT (Activated Partial Thromboplastin Time)

Normal Range: 30-40 seconds

Therapeutic Range for Heparin: 1.5-2x normal (60-80 seconds)

The aPTT measures the intrinsic pathway and is used to monitor unfractionated Heparin therapy.

Heparin Key Points

Mechanism: Enhances antithrombin III activity (inactivates thrombin and factor Xa)

Onset: Immediate (IV)

Duration: Short (hours)

Types:

Heparin Administration Safety

For IV Unfractionated Heparin:

• Must use infusion pump
• aPTT checked 6 hours after initiation or dose change
• Dose adjusted based on protocol

For SubQ Enoxaparin (Lovenox):

• Do NOT expel air bubble before injection
• Inject into abdomen, 2 inches from umbilicus
• Do NOT rub injection site
• Rotate sites

Elevated aPTT (> 80 seconds) or Heparin Overdose

Signs:

• Bleeding (same as Warfarin)
• Hematoma at injection sites

Antidote: Protamine Sulfate

• Given slowly IV
• 1 mg protamine neutralizes approximately 100 units of heparin
• Risk of hypotension and anaphylaxis (derived from fish)

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Heparin-Induced Thrombocytopenia (HIT)

HIT is a serious complication of heparin therapy where antibodies form against platelets, causing both thrombocytopenia AND paradoxical clotting.

Onset: 5-10 days after starting heparin (or sooner if previous exposure)

Diagnosis:

• Platelet drop > 50% from baseline
• New thrombosis

Management:

• Stop ALL heparin immediately (including flushes)
• Use alternative anticoagulant (argatroban, bivalirudin)
• Never give heparin to this patient again

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Comparison of Anticoagulants

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Direct Oral Anticoagulants (DOACs)

Newer anticoagulants (rivaroxaban, apixaban, dabigatran) are increasingly common.

Advantages:

• No routine monitoring required
• Fixed dosing
• Fewer drug/food interactions

Disadvantages:

• Limited reversal options (though improving)
• Renal dosing considerations

Antidotes:

• Dabigatran (Pradaxa): Idarucizumab (Praxbind)
• Rivaroxaban/Apixaban: Andexanet alfa (Andexxa)

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Bleeding Precautions for All Anticoagulants

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On the Exam

The NCLEX frequently tests:

• Which lab monitors which drug (INR = Warfarin, aPTT = Heparin)
• Therapeutic ranges (INR 2-3, aPTT 60-80)
• Antidotes (Vitamin K vs. Protamine sulfate)
• Patient education (dietary consistency, bleeding signs)
• HIT recognition and management

Priority Tip: If a patient on anticoagulants shows signs of bleeding with elevated lab values, hold the medication and notify the provider immediately.