Clinical UM Guideline

This document addresses the use of the prothrombin time (PT) test, also referred to as protime, an in vitro laboratory assay used to assess the extrinsic coagulation pathway. The PT test is commonly used to measure the effect of warfarin (anticoagulation therapy) and regulate its dosing. The International Normalized Ratio (INR), commonly reported with PT, is a standardized calculation derived from the PT results and allows results to be compared across different laboratories.

Note: Please see the following for information on home PT testing:

• CG-DME-30 Prothrombin Time Self-Monitoring Devices

Note: For partial thromboplastin time (PTT) testing, see the following:

• CG-LAB-36 Partial Thromboplastin Time (PTT)

Note: For PT testing performed in low-risk invasive procedures, see the following:

• CG-MED-61 Preoperative Testing for Low Risk Invasive Procedures and Surgeries

Note: See the following for other preoperative or screening tests:

• CG-MED-62 Resting Electrocardiogram Screening in Adults

Note: For a high-level overview of this document, please see “Summary for Members and Families” below. 

Medically Necessary:

Prothrombin time or International Normalized Ratio testing is considered medically necessary for any of the following indications:

1. Monitor warfarin therapy:
   1. Monitor warfarin therapy (effect and dosing); or
   2. Transition from warfarin to heparin therapy;
      or
2. Diagnostic evaluation of hemorrhage or thrombosis:
   1. Evaluation of abnormal bleeding suggestive of coagulopathy (for example, hemorrhage, petechiae, hematoma); or
   2. Evaluation of possible thrombosis (for example, swollen extremity with or without trauma);
      or
3. Evaluation of individuals with conditions associated with coagulopathy, including, but not limited to:
   1. Congenital or acquired bleeding disorder; or
   2. Liver disease or failure (including Wilson’s disease and hemochromatosis); or
   3. Disseminated intravascular coagulation (DIC); or
   4. Lupus erythematosus or other inhibitor states (for example, factor VIII inhibitor, lupus anticoagulant); or
   5. Sepsis or infectious processes associated with abnormal coagulation; or
   6. Malignant neoplasms (for example, acute and chronic leukemia); or
   7. Salicylate poisoning; or
   8. Vitamin K deficiency; or
   9. Intestinal conditions (for example, fistula, malabsorption syndrome, colitis, chronic diarrhea); or
   10. Organ transplantation; or
   11. Renal failure or nephrotic syndrome; or
   12. Hypercoagulable states, arterial or venous thrombosis;
       or
4. Evaluation prior to an invasive procedure when any of the following criteria (1 or 2) are met:
   1. The same test has not been performed in the previous 30 days; or
   2. Repeat testing within the 30 day window in an individual who meets any of the following conditions:
      1. Personal or family history of bleeding or thrombosis; or
      2. Current or recent anticoagulation therapy; or
      3. Documented or suspected coagulation abnormalities; or
      4. Age 65 or older.

Repeat prothrombin time or International Normalized Ratio testing is considered medically necessary when used to:

1. Monitor response to therapy; or
2. Assess a change in clinical status, such as new or unexplained bleeding, thrombosis, or suspicion of disease progression or intercurrent illness affecting coagulation.

Not Medically Necessary:

Prothrombin time or International Normalized Ratio testing is considered not medically necessary when the criteria above are not met.

This document describes clinical studies and expert recommendations, and explains whether certain tests to evaluate blood clotting function, called prothrombin time and International Normalized Ratio, are appropriate. The following summary does not replace the medical necessity criteria or other information in this document. The summary may not contain all of the relevant criteria or information. This summary is not medical advice. Please check with your healthcare provider for any advice about your health.

Key Information

Prothrombin time (PT) is a blood test that helps measure how well a person’s blood is clotting. The International Normalized Ratio (INR) is a standardized calculation derived from the PT results and allows them to be compared across different laboratories. PT/INR are commonly used to check the effect of warfarin, a medication that helps prevent blood clots. PT/INR testing is also used to help find bleeding or clotting problems, check liver function, and assess risk before certain medical procedures. PT testing works by measuring how long it takes for a sample of blood to form a clot. Keeping the PT/INR in the right range helps make sure the blood does not clot too easily or too slowly. Doctors use this test often for people taking warfarin, especially after a dose change or if there is a change in health. PT/INR testing is also used in people with liver disease, infections, certain cancers, vitamin K deficiency, kidney problems, or other health issues that affect blood clotting. It can also help doctors decide if it is safe to do surgery or other procedures where bleeding is a risk factor. However, PT/INR testing is generally not needed unless one of these reasons is present. Doing the test without a clear reason may lead to treatments that are not necessary.

What the Studies Show

PT/INR testing helps guide care for people taking warfarin. High-quality studies show they are useful for checking if warfarin is working and whether its dose needs adjusting. Studies also show that liver problems, infections, cancer, and kidney disease can all change PT levels. PT is also a key part of checking clotting in people with conditions like leukemia or lupus, or in those being tested for bleeding disorders. Guidelines from medical groups such as the American Association for the Study of Liver Diseases (AASLD) and the National Comprehensive Cancer Network (NCCN) support PT as a standard test in these cases. Research also shows that PT is helpful when preparing for surgery in people with certain health risks. Testing is generally recommended only when there is a history of bleeding, signs of clotting problems, or other risks.

When is PT/INR Testing Clinically Appropriate?

PT or INR testing may be appropriate in these situations:

• To monitor warfarin therapy (to check its effect or guide dosing)
• During a change from warfarin to heparin
• To evaluate signs of abnormal bleeding or blood clots
• In people with bleeding or clotting conditions, including:
  • Inherited or acquired bleeding disorders
  • Liver disease (such as Wilson’s disease or hemochromatosis)
  • Disseminated intravascular coagulation (DIC)
  • Lupus or other conditions affecting clotting factors
  • Sepsis or infections linked to clotting problems
  • Blood cancers (like leukemia)
  • Salicylate (aspirin) poisoning
  • Vitamin K deficiency
  • Intestinal diseases (such as Crohn’s or chronic diarrhea)
  • Organ transplant
  • Kidney failure or nephrotic syndrome
  • Risk of blood clots in veins or arteries
• Before surgery or an invasive procedure if:
  • PT/INR has not been done in the past 30 days
  • It has been done within 30 days but there is:
    • A personal or family history of bleeding or blood clots
    • Use of heparin
    • Signs of blood clotting problems
    • Age 65 or older
• To check response to treatment
• To evaluate new or worsening bleeding or blood clots

When is this not Clinically Appropriate?

PT/INR testing is not appropriate when none of the above conditions are present. Better studies are needed to know if routine testing without risk factors improves health. PT/INR testing is not clinically appropriate in situations other than those listed above.

(Return to Description)

The following codes for treatments and procedures applicable to this guideline are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services are Medically Necessary:

When services may be Medically Necessary when criteria are met:
For the procedure code listed above for all other diagnoses.

When services are Not Medically Necessary:
For the procedure code listed above when criteria are not met.​

Summary

Prothrombin time (PT) and international normalized ratio (INR) testing are medically necessary in several key clinical situations, including monitoring warfarin therapy, evaluating hemorrhage or thrombosis, assessing conditions associated with coagulopathy, and performing pre-procedural risk assessment when certain criteria are met. These tests support diagnosis and management of a wide range of disorders, such as bleeding abnormalities, liver disease, disseminated intravascular coagulation (DIC), malignancy-associated coagulopathy, vitamin K deficiency, renal failure, and hypercoagulable states, and help determine when anticoagulation therapy is safe or requires adjustment. Repeat testing is appropriate when monitoring therapy or reassessing a change in clinical status.

PT or INR provide a measure of the extrinsic coagulation pathway and are essential for managing warfarin therapy, where maintaining a therapeutic INR is critical for preventing conditions like atrial fibrillation-related stroke or venous thromboembolism. These tests also play a role in initial evaluation of bleeding disorders, lupus anticoagulant, coagulation abnormalities in leukemia, liver dysfunction, and other systemic conditions affecting clotting factor production. Guidelines from groups such as the National Comprehensive Cancer Network (NCCN), American Association for the Study of Liver Diseases (AASLD), and the American Academy of Cardiology (ACC) reinforce PT’s role as a standard component of evaluation in suspected coagulopathies, malignancies, liver disease, and anticoagulant-related bleeding.

Liver disease, renal impairment, malignancy, and systemic inflammatory conditions can all disrupt coagulation pathways, making PT a useful indicator of disease progression or hepatic synthetic failure. PT or INR also aid in pre-procedural risk assessment, though routine testing without risk factors is not typically recommended; instead, testing is guided by clinical history, recent laboratory results, and factors such as age over 65 or suspected coagulation abnormalities. When none of the outlined criteria are met, PT or INR testing is considered not medically necessary.

Discussion

PT and INR measure the function of the extrinsic and common coagulation pathways by timing how long it takes plasma to clot. Normal PT values range from 9 to13 seconds while higher values indicate a prolonged clotting time, suggesting potential issues with clotting factors such as fibrinogen, factor V, VII, X, and prothrombin. INR is a standardized calculation derived from the PT results, ensuring consistency in results obtained by different laboratories. The normal range for INR is around 0.8 to 1.2, with higher INR values indicating a slower clotting time and an increased risk of bleeding (Zaidi, 2024).

Extrinsic coagulation pathway factors are produced in the liver, and their production is dependent on adequate vitamin K activity. The commonly prescribed anticoagulant drug warfarin works by blocking the body from reusing vitamin K, which the liver needs to make clotting factors. With less active vitamin K, the liver makes fewer clotting proteins, so blood clots more slowly. PT is commonly used to measure the effect of the warfarin and regulate its dosing. Vitamin K deficiency and increased warfarin levels result in a prolonged PT.

PT, often reported with the INR, is widely used in several major clinical settings: (1) monitoring effects of warfarin, where therapeutic INR targets generally range from 2.0 to 3.0 depending on the reason for anticoagulant therapy, (2) diagnosing inherited or acquired bleeding disorders by checking for deficiencies in specific blood clotting factors (factors I, II, V, VII, and X), (3) assessing liver function, since the liver produces most of the clotting factors and a prolonged PT can indicate liver disease, such as cirrhosis or hepatitis, (4) checking vitamin K levels due to the essential role of vitamin K in production of several clotting factors, and (5) preoperative screening to assess an individual’s overall clotting ability and determine the risk of excessive bleeding during the procedure. Thus, PT testing serves as a critical tool for both anticoagulant management and for identifying defects across much of the coagulation cascade.

Warfarin Therapy

The prescription drug warfarin is a type of anticoagulant (“blood thinning”) medication administered to prevent harmful blot clots from forming or growing larger. It works by interfering with the synthesis of vitamin K-dependent clotting factors, making the blood take longer to clot. Warfarin is prescribed for people with certain types of irregular heartbeat (for example, atrial fibrillation), people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. It is also used for treatment and prevention of venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). The effect of warfarin is monitored using the PT or INR test with the goal of maintaining the INR within a specific target range (commonly between 2.0 and 3.0). If the INR is outside of the desired range, the dosage of warfarin may be adjusted. For example, if the INR is low, the dose of warfarin may be increased and if the INR is high, a decrease in the dose may be considered. Once the dose and INR are stable, individuals can usually be monitored with INR testing every 4 to 6 weeks. After any dose adjustment, the INR should be rechecked more frequently (for example, in 1 to 2 weeks, or sooner if significantly out of range) until it stabilizes within the therapeutic range (Tideman, 2015).

PT and Coagulation Disorders

A combination of coagulation laboratory testing, including PT, activated partial thromboplastin time (APTT), bleeding time and platelet count may be used during the initial diagnostic phase of a bleeding disorder. These findings allow for a provisional classification of the bleeding disorder, guiding subsequent analysis. The presence of a normal PT with a prolonged APTT may be indicative of hemophilia A or B or von Willebrand disease (Srivastava, 2013).

In lupus, particularly antiphospholipid syndrome (APS), the APTT is often prolonged due to lupus anticoagulant, autoantibodies directed against phospholipid-binding proteins that interfere with phospholipid-dependent clotting assays. Lupus anticoagulant is not associated with bleeding; but does represent a prothrombotic risk. In lupus/APS, PTT serves primarily as a screening and diagnostic clue for lupus anticoagulant, rather than a measure of bleeding tendency (Jacobs, 2022). Initial routine tests like prothrombin time (PT) are also performed to rule out other coagulation factor deficiencies or inhibitors, or the effects of anticoagulant drugs. A guideline from the International Society on Thrombosis and Haemostasis Scientific and Standardization Subcommittee (ISTH-SSC) recommends testing of PT, APTT, and thrombin time before lupus anticoagulant testing in cases of unknown clinical and pharmacological history (Tripodi, 2020).

The 2020 ACC Expert Consensus Decision Pathway (Tomaselli, 2020) recommends that in patients presenting with clinically relevant bleeding while on oral anticoagulants, basic coagulation testing should always include PT and APTT, even though these tests have important limitations for direct oral anticoagulants (DOACs). For vitamin K antagonists such as warfarin, PT/INR is reliable for guiding management, but for DOACs, PT/APTT may only provide qualitative information and lack sensitivity or specificity depending on the agent and assay used. Specialized assays (e.g., dilute thrombin time for dabigatran, chromogenic anti-factor Xa assays for apixaban, edoxaban, rivaroxaban) are preferred where available, but they are not universally accessible. The consensus emphasizes that a normal PT/APTT does not reliably exclude clinically significant DOAC levels, while a prolonged result may suggest on- or above-therapy drug levels, though interpretation is reagent-dependent. Thus, PT and APTT are recommended as initial, widely available screening tools, with the understanding that their limitations require cautious interpretation, and that they should be supplemented with drug-specific assays when clinical decisions hinge on accurate anticoagulant quantitation.

Disseminated intravascular coagulation (DIC), typically an acute process, is a consumptive coagulopathy triggered by systemic activation of the coagulation cascade, often triggered by sepsis, trauma, or other critical illness. There is sudden, systemic activation of coagulation, leading to rapid consumption of clotting factors and platelets, which manifests as simultaneous microvascular thrombosis and bleeding. Individuals at highest risk include those with severe infections, trauma, or underlying thrombophilia, where pre-existing procoagulant states amplify the dysregulated response. There is a less common form of DIC, chronic or subacute. This form is more often associated with solid tumors or large aortic aneurysms, where coagulation is activated at a slower rate, and the body partially compensates. These individuals may present with more subtle laboratory abnormalities and a higher risk of thrombosis than bleeding. Clinical monitoring relies on serial laboratory tests including prolonged PT, thrombocytopenia, elevated fibrin degradation products (e.g., D-dimer), and reduced fibrinogen (Zaidi, 2024). These status of these clinical indicators reflect ongoing thrombin generation, factor consumption, and impaired fibrinolysis.

The NCCN Clinical Practice Guidelines (CPGs) for acute myeloid leukemia (AML) (V3.2026) note the following about both AML and acute promyelocytic leukemia (APL):

Coagulopathy is common at presentation in many leukemias; it is therefore standard clinical practice to screen for coagulopathy by evaluating prothrombin time (PT), partial thromboplastin time (PTT), and fibrinogen activity as part of the initial evaluation and before performing any invasive procedure.

Likewise, the NCCN guideline for acute lymphoblastic leukemia (ALL) (V2.2025) notes that:

The initial workup for patients with ALL should include a thorough medical history and physical examination, along with laboratory and imaging studies (where applicable). Laboratory studies include a complete blood count (CBC) with differential, a blood chemistry profile, liver function tests, a disseminated intravascular coagulation panel (including measurements for D-dimer, fibrinogen, prothrombin time, and partial thromboplastin time).

In the NCCN guideline for hepatocellular carcinoma (HCC) (V2.2025), PT testing is included in liver function assessment and in the workup after HCC confirmed. The guideline notes that:

An initial assessment of hepatic function involves liver function testing including measurement of serum levels of bilirubin, aspartate aminotransferase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), measurement of prothrombin time (PT) expressed as international normalized ratio (INR), albumin, and platelet count (surrogate for portal hypertension).

In the NCCN CPG for cancer-associated venous thromboembolic disease (V3.2025), baseline PT and APTT are recommended in the initial evaluation of suspected venous thromboembolism (VTE), including acute DVT and pulmonary embolism (PE). Obtained alongside complete blood count (CBC), renal and hepatic function tests, and imaging, these assays help detect coagulopathies that may alter management; for instance, an abnormal PT or APTT (excluding lupus anticoagulant-related prolongation) may indicate a bleeding disorder and serve as a relative contraindication to full-dose anticoagulation.

Salicylate poisoning can interfere with the production of clotting factors in the liver, causing prolonged PT due to hypoprothrombinemia. Salicylate intoxication can be accidental, but even therapeutic doses of aspirin can cause chronic intoxication resulting in severe coagulopathy in individuals with chronic kidney disease (CKD) (Kato, 2025). The deficiency in prothrombin is reflected in a prolonged PT or elevated INR indicating a higher risk of bleeding.

Vitamin K is absorbed in the bowel, and conditions like chronic diarrhea, Crohn’s disease or other inflammatory diseases can impair intestinal absorption. Individuals with inflammatory bowel disease (IBD) may have a significantly prolonged PT, especially in cases with an intestinal fistula (Li, 2018).

Careful monitoring of blood coagulation status is important in organ transplant recipients, especially in the post-operative period, to manage complications from medications and the transplant process itself. The process of the organ being without blood flow and then being reperfused can cause ischemia-reperfusion injury (IRI) which may trigger thrombosis and inflammation in the graft. An immune response to the transplanted organ can also activate the coagulation cascade. In liver transplant candidates, PT is a key component of the Model for End-Stage Liver Disease (MELD) score, which measures the severity of chronic liver disease (Akamatsu, 2017; Vandyck, 2023).

Thrombosis and bleeding are among the most common causes of morbidity and mortality in patients with renal disease. Nephrotic syndrome may lead to a loss of some anticoagulants and a potential increase in prothrombotic factors, while renal failure can also lead to hypercoagulability. Increased thrombosis risk is thought to be due to the chronic activation of the coagulation cascade (Ribic, 2016). Warfarin therapy is a common option for individuals with renal disease. Individuals with renal impairment may require lower doses of warfarin to stay within the therapeutic range due to altered metabolism, and regular monitoring is required to maintain a stable INR.

Liver Disorders

Liver disease profoundly alters coagulation because the liver produces nearly all clotting factors, anticoagulant proteins, and regulators of fibrinolysis. Damage to the liver reduces synthesis of procoagulant factors (II, V, VII, IX, X, XI) and anticoagulants (protein C, protein S, antithrombin), while portal hypertension causes thrombocytopenia and vitamin K deficiency further impairs factor production. This creates a “rebalanced but unstable” hemostatic state in which an affected individual faces risks of both bleeding (from decreased clotting capacity and platelet dysfunction) and thrombosis (from loss of natural anticoagulants and enhanced endothelial activation). Individuals with liver cirrhosis and splenomegaly have a significant risk of coagulation dysfunction. In a retrospective study by Lv (2023), 80% of affected individuals had coagulation dysfunction.

A 2022 practice guidance by the AASLD outlines the diagnosis and management of Wilson’s disease (Schilsky, 2025). In Wilson’s disease, an autosomal recessive disorder caused by ATP7B mutations, impaired biliary copper excretion results in progressive hepatic copper accumulation. The ensuing hepatocellular injury can lead to cirrhosis or acute liver failure and is frequently associated with clinically significant coagulopathy. Characteristic defects include reduced synthesis of clotting factors, a vitamin K-independent coagulopathy, and in fulminant presentations, profound coagulopathy that is typically unresponsive to vitamin K administration. Superimposed hemolysis and hypersplenism-related thrombocytopenia may further exacerbate bleeding risk, while disruption of the balance between procoagulant and anticoagulant pathways also predisposes patients to thrombotic events. The guidance recommends tests of hepatic synthetic function at baseline and over time in Wilson’s disease, and notes that INR is a good measure of hepatic synthetic function.

Hereditary hemochromatosis (HH) is the pathophysiologic predisposition to increased, inappropriate absorption of dietary iron which may lead to the development of life-threatening complications of cirrhosis, hepatocellular carcinoma (HCC), diabetes, and heart disease (Bacon, 2011). HH is an autosomal recessive disorder that results from a defect in the HFE gene causing iron to accumulate in organs like the liver, pancreas, and heart. PT is normal early in the disease course of HH, but it can become prolonged in later stages as iron overload causes liver damage or cirrhosis. A prolonged PT can be a marker of advanced liver disease in hemochromatosis.

Preprocedural Evaluation

Virchow’s triad explains venous thrombosis as the interaction of stasis, endothelial injury, and hypercoagulability (Kushner, 2024). Stasis from immobility or venous obstruction slows blood flow, endothelial injury from surgery, trauma, or catheters disrupts the vessel’s anticoagulant surface, and inherited or acquired prothrombotic states such as malignancy, pregnancy, or hormonal therapy increase clotting potential. In practice, most individuals exhibit overlapping risks across these mechanisms, which collectively drive the development of deep vein thrombosis (DVT). Hypercoagulability status is assessed by coagulation assays which would include PT.

Current professional guidelines, including the American Society of Anesthesiologists (ASA) Practice Advisory for Preanesthesia Evaluation (Apfelbaum, 2012), do not endorse routine preoperative PT testing based solely on age. However, adults aged 65 years and older have a higher prevalence of coagulation abnormalities due to age-related physiologic and pathologic changes, which may result in or contribute to postoperative complications (Kruse-Jarres, 2015; Lee, 2021; Malpani, 2020; Mari, 2008). While chronological age alone is not an independent indication for preoperative coagulation testing, selective PT testing may be appropriate in older adults with additional risk factors or suspicious findings.

Analyses of large surgical databases, including studies by Taylor (2021) and Benarroch-Gampel (2012), evaluated the utility of routine preoperative laboratory testing such as PT performed within 30 days prior to elective procedures. Both studies defined the preoperative testing window as 30 days and found that while abnormal laboratory values were common, these abnormalities did not correlate with increased postoperative complications, morbidity, or mortality. The 30-day timeframe is therefore used as a standard reference period to capture relevant preoperative laboratory assessments while minimizing unnecessary repeat testing, as results within this interval are generally considered clinically valid and reflective of the individual’s current coagulation status unless new risk factors are present.

International Normalized Ratio (INR): A standardized system established by the World Health Organization (WHO) and the International Committee on Thrombosis and Hemostasis (ICTH) for reporting the results of blood coagulation (clotting) tests using the international sensitivity index for the particular thromboplastin reagent and instrument combination utilized to perform the test.

Prothrombin time (PT): A test belonging to a group of blood tests that assess the clotting ability of blood; also known as the protime or PT test.

Peer Reviewed Publications:

1. Akamatsu N, Sugawara Y, Kanako J, et al. Low platelet counts and prolonged prothrombin time early after operation predict the 90 days morbidity and mortality in living-donor liver transplantation. Ann Surg. 2017; 265:166-172.
2. Benarroch-Gampel J, Sheffield KM, Duncan CB, et al. Preoperative laboratory testing in patients undergoing elective, low-risk ambulatory surgery. Ann Surg. 2012; 256(3):518-528.
3. Kato Y, Fukunaga N, Misumi T. Severe coagulopathy associated with unintentional salicylate intoxication in a postsurgical patient. CJC Open. 2024; 7(1):120-122.
4. Kruse-Jarres R. Acquired bleeding disorders in the elderly. Hematology Am Soc Hematol Educ Program. 2015; 2015:231-236.
5. Kushner A, West WP, Khan et al. Virchow Triad. 2024 Jun 7. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan -. PMID: 30969519.
6. Lee KC, Lee IO. Preoperative laboratory testing in elderly patients. Curr Opin Anaesthesiol. 2021; 34(4):409-414.
7. Li Y, Ren J-A, Wang G-F, et al. Impaired coagulation status in the Crohn’s disease patients complicated with intestinal fistula. Chin Med J (Engl). 2018; 131(5):567-573.
8. Lv Y, Liu N, Li Y, et al. Coagulation dysfunction in patients with liver cirrhosis and splenomegaly and its countermeasures: a retrospective study of 1522 patients. Dis Markers. 2023; 2023:5560560.
9. Malpani R, Mclynn RP, Bovonratwet P, et al. Coagulopathies are a risk factor for adverse events following total hip and total knee arthroplasty. Orthopedics. 2020; 43(4):233-238.
10. Mari D, Ogliari G, Castaldi D, et al. Hemostasis and ageing. Immun Ageing. 2008; 5:12.
11. Ribic C, Crowther M. Thrombosis and anticoagulation in the setting of renal or liver disease. Hematology Am Soc Hematol Educ Program. 2016; 2016(1):188-195.
12. Taylor GA, Liu JC, Schmalbach CE, et al. Preoperative laboratory testing among low-risk patients prior to elective ambulatory endocrine surgeries: a review of the 2015-2018 NSQIP cohorts. Am J Surg. 2021; 222(3):554-561.
13. Tideman PA, Tirimacco R, St John A, Roberts GW. How to manage warfarin therapy. Aust Prescr. 2015; 38:44-48.
14. Vandyck KB, Rusin W, Mondal S, Tanaka KA. Coagulation management during liver transplantation: monitoring and decision making for hemostatic interventions. Curr Opin Organ Transpl. 2023; 28:404-411.
15. Zaidi SRH, Rout P. Interpretation of blood clotting studies and values (PT, PTT, APTT, INR, Anti-Factor Xa, D-Dimer). 2024 Jun 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan -. PMID: 38861642.

Government Agency, Medical Society, and Other Authoritative Publications:

1. Apfelbaum JL, Connis RT, Nickinovich DG, et al.; American Society of Anesthesiologists (ASA) Task Force on Preanesthesia Evaluation on Standards and Practice Parameters. Practice advisory for preanesthesia evaluation: an updated report by the ASA Task Force on Preanesthesia Evaluation. Anesthesiology. 2012; 116(3):522-538.
2. Bacon BR, Adams PC, Kowdley KV, et al. Diagnosis and management of hemochromatosis: 2011 practice guideline by the American Association for the Study of Liver Diseases. Hepatology. 2011; 54(1):328-343.
3. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US). Prothrombin Time Test and INR (PT/INR). Last updated May 15, 2024. Available at: https://medlineplus.gov/lab-tests/prothrombin-time-test-and-inr-ptinr/. Accessed on February 13, 2026.
4. NCCN Clinical Practice Guidelines in Oncology^®. ^© 2026 National Comprehensive Cancer Network, Inc. For additional information visit the NCCN website: http://www.nccn.org/index.asp. Accessed on February 13, 2026.
   • Acute Lymphoblastic Leukemia V2.2025. Revised June 27, 2025.
   • Acute Myeloid Leukemia. V3.2026. Revised November 24, 2025.
   • Cancer-Associated Venous Thromboembolic Disease. V3.2025. Revised November 6, 2025.
   • Hepatocellular Carcinoma. V2.2025. Revised October 22, 2025.
5. Schilsky ML, Roberts EA, Bronstein JM, et al. A multidisciplinary approach to the diagnosis and management of Wilson disease: 2022 practice guidance on Wilson disease from the American Association for the Study of Liver Diseases. Hepatology. 2025; 82(3):E41-E90.
6. Srivastava A, Brewer AK, Mauser-Bunschoten EP, et al. Treatment Guidelines Working Group on behalf of the World Federation of Hemophilia. Guidelines for the management of hemophilia. Haemophilia. 2013; 19(1):e1-47.
7. Tomaselli GF, Mahaffey KW, Cuker A, et al. 2020 ACC expert consensus decision pathway on management of bleeding in patients on oral anticoagulants: a report of the American College of Cardiology Solution Set Oversight Committee. J Am Coll Cardiol. 2020; 76(5):594-622.
8. Tripodi A, Cohen H, Devreese KMJ. Lupus anticoagulant detection in anticoagulated patients. Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis. J Thromb Haemost. 2020; 18(7):1569-1575.

1. National Blood Clot Alliance. Warfarin. https://www.stoptheclot.org/about-clots/blood-clot-treatment/warfarin/. Accessed on February 13, 2026.

INR
International Normalized Ratio
prothrombin time
protime
PT

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