Prothrombin Complex (Prothrombin Time, PT) with INR Calculation and International Sensitivity Index (ISI) for Serum
This test measures how long it takes for blood to clot, helping assess blood clotting function and identify potential bleeding or clotting disorders.
["Your blood clotting ability and risk of abnormal bleeding or clotting are evaluated here."]
Key facts at a glance
- LOINC
- 85358-0
- Short code
- PS-prothrom cmplx IgM SerPl IA-aCnc
- Synonyms
- PS-prothrom cmplx IgM SerPl IA-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- ia
- CPT
- 82784
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What This Test Measures
The test evaluates the time it takes for blood to clot, which is influenced by several clotting factors in your blood. This includes measuring the prothrombin time (PT), a standard test used to monitor how effectively your blood clots. The International Normalized Ratio (INR) is calculated to standardize results across different labs, accounting for variations in test reagents. The International Sensitivity Index (ISI) reflects how sensitive the test is to changes in clotting factors.
Why It’s Done
This test is often used to monitor conditions like liver disease, where clotting factors may be affected, or to check blood thinners (anticoagulants) like warfarin. It helps ensure these medications are at the right level to prevent excessive clotting without causing dangerous bleeding.
Common Conditions Monitored
Prothrombin time is commonly checked in people with liver disease, blood clotting disorders, or those taking anticoagulants. It may also be used before surgeries or procedures that could cause bleeding.
What to Expect Before the Test
No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it involves a blood draw for other tests. Wear comfortable clothing and bring any medications you’re currently taking.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Prothrombin Time (PT) with INR
Frequently asked questions
How long your blood takes to clot can indicate problems with clotting factors, liver function, or the effectiveness of blood thinners. High PT/INR values may suggest bleeding risks, while low values could indicate an increased risk of clots. This test is critical for managing conditions like thrombophilia, liver disease, or anticoagulant therapy.
What do my results mean?
Can I eat or drink before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy