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🧪 What is Prothrombin Time (PT) with INR?

Prothrombin Time (PT) measures the time it takes for blood plasma to clot after the addition of tissue factor (thromboplastin). It evaluates the extrinsic and common coagulation pathways, primarily involving clotting factors I (fibrinogen), II (prothrombin), V, VII, and X.

The International Normalized Ratio (INR) standardizes PT results, allowing consistent interpretation across different labs and reagents, especially important for monitoring warfarin therapy.

❓ Why is the Test Done?

To:

Evaluate bleeding disorders or unexplained bleeding
Monitor oral anticoagulant (warfarin) therapy
Assess liver function (synthesis of clotting factors)
Detect vitamin K deficiency
Investigate disseminated intravascular coagulation (DIC)
Preoperative screening for coagulation status

📊 Normal Ranges

Test	Normal Range
PT	11 – 13.5 seconds
INR	0.8 – 1.2 (non-anticoagulated individuals)

Therapeutic INR range for most indications: 2.0 – 3.0
For mechanical heart valves or high-risk patients: 2.5 – 3.5

📈 Interpretation of Results

Result	Possible Implications
Prolonged PT / INR >1.2	Liver disease, vitamin K deficiency, warfarin overdose, DIC, factor deficiencies (VII, X, V, II, fibrinogen)
Shortened PT	Usually not clinically significant
Therapeutic INR	Indicates effective anticoagulation
Subtherapeutic INR	Increased risk of thrombosis
Supratherapeutic INR	Increased bleeding risk

🧠 Associated Conditions

Condition	Details
Liver disease	Reduced synthesis of clotting factors
Vitamin K deficiency	Impaired clotting factor activation
Anticoagulant therapy	Warfarin monitoring
Disseminated Intravascular Coagulation (DIC)	Consumptive coagulopathy
Coagulation factor deficiencies	Congenital or acquired defects

🔄 Related / Follow-Up Tests

Activated Partial Thromboplastin Time (aPTT) – evaluates intrinsic pathway
Platelet count
Fibrinogen level
D-dimer
Liver function tests
Vitamin K levels

✅ Fasting Required?

Test	Fasting Required
PT with INR	❌ No

📝 Summary Table

Parameter	Details
What	Measures clotting time via extrinsic pathway; standardized as INR
Why	Monitor warfarin therapy, assess bleeding risk, liver function
Normal Range	PT: 11–13.5 sec; INR: 0.8–1.2
Prolonged PT/INR	Liver disease, vitamin K deficiency, anticoagulant overdose
Associated Conditions	Liver disease, DIC, vitamin K deficiency, warfarin use
Follow-up Tests	aPTT, platelet count, fibrinogen, liver function tests
Fasting Required	❌ No

Prothrombin Time (PT with INR)

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