Prothrombin Time (INR) Home Testing Devices

Number: 0173

Table Of Contents

Applicable CPT / HCPCS / ICD-10 Codes


Scope of Policy

This Clinical Policy Bulletin addresses prothrombin time (INR) home testing devices.

  1. Medical Necessity

    Aetna considers prothrombin time home testing units/home INR testing (e.g., the Coag-Sense Self-Test PT/INR Monitoring System, the CoaguChek XS Plus System, and the INRatio® 2 PT/INR Monitoring System) medically necessary durable medical equipment for persons who require chronic oral anticoagulation with warfarin for a mechanical heart valve, ventricular assist device, chronic atrial fibrillation, deep venous thrombosis, pulmonary embolism, venous embolism and thrombosis of deep vessels of lower extremity, or hypercoagulable states (e.g., antithrombin III deficiency, Factor V Leiden, protein C deficiency, and protein S deficiency, etc) when all of the following criteria are met:

    1. The expected need for home INR testing is 6 or more months; and
    2. The person must have been anticoagulated for at least 3 months prior to use of the home INR devices; and
    3. Self-testing with the device should not occur more frequently than once a week.

    Aetna considers additional hardware/software systems needed for down-loading data from prothrombin time home testing units to computers for the management of anticoagulation as not medically necessary convenience items.

  2. Experimental and Investigational

    Aetna considers prothrombin time home testing units experimental and investigational for all other indications (e.g., arterial embolism to the eye, atrial flutter, and Kawasaki disease) because its effectiveness for indications other than the ones listed above has not been established.


CPT Codes / HCPCS Codes / ICD-10 Codes

Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":

CPT codes covered if selection criteria are met:

93792 Patient/caregiver training for initiation of home international normalized ratio (INR) monitoring under the direction of a physician or other qualified health care professional, face-to-face, including use and care of the INR monitor, obtaining blood sample, instructions for reporting home INR test results, and documentation of patient's/caregiver's ability to perform testing and report results
93793 Anticoagulant management for a patient taking warfarin, must include review and interpretation of a new home, office, or lab international normalized ratio (INR) test result, patient instructions, dosage adjustment (as needed), and scheduling of additional test(s), when performed

HCPCS codes covered if selection criteria are met:

G0248 Demonstration, prior to initial use, of home INR monitoring for patient with either mechanical heart valve(s), chronic atrial fibrillation, or venous thromboembolism who meets Medicare coverage criteria, under the direction of a physician; includes: face-to-face demonstration of use and care of the INR monitor, obtaining at least one blood sample, provision of instructions for reporting home INR test results, and documentation of patient ability to perform testing prior to its use
G0249 Provision of test materials and equipment for home INR monitoring of patient with either mechanical heart valve(s), chronic atrial fibrillation, or venous thromboembolism who meets Medicare coverage criteria; includes provision of materials for use in the home and reporting of test results to physician; not occurring more frequently than once a week
G0250 Physician review, interpretation and patient management of home INR testing for a patient with either mechanical heart valve(s), chronic atrial fibrillation, or venous thromboembolism who meets Medicare coverage criteria; includes face-to-face verification by the physician that the patient uses the device in the context of the management of the anticoagulation therapy following initiation of the home INR monitoring; not occurring more frequently than once a week

ICD-10 codes covered if selection criteria are met:

D68.51 - D68.62 Thrombophilia (Antithrombin III deficiency, Factor V leiden, Protein C deficiency, Protein S deficiency)
I26.01 - I26.99 Pulmonary embolism
I27.82 Chronic pulmonary embolism
I48.0, I48.11, I48.19, I48.20, I48.21, I48.91 Atrial fibrillation
I80.00 - I80.9 Phlebitis and thrombophlebitis of upper and lower extremities and unspecified site
I82.401 - I82.5Z9 Embolism and thrombosis of deep veins of lower extremity
I82.621 - I82.629 Acute embolism and thrombosis of deep veins of upper extremity
I82.721 - I82.729 Chronic embolism and thrombosis of deep veins of upper extremity
T80.0XX+, T81.718+, T81.72x+
T82.817+ - T82.818+ [I26.90, I26.99 also required]
Pulmonary embolism and infarction
Z95.2 Presence of prosthetic heart valve
Z95.811 Presence of heart assist device

ICD-10 codes not covered for indications listed in the CPB (not all-inclusive):

H34.9 Unspecified retinal vascular occlusion [arterial embolism to the eye]
I48.3, I48.4, I48.92 Atrial flutter
M30.3 Mucocutaneous lymph node syndrome [Kawasaki disease]


This policy is consistent with the conclusions of an assessment from the Centers for Medicare & Medicaid Services (CMS, 2008).

Prothrombin time home testing systems are portable, battery-operated instruments for the quantitative determination of prothrombin time from finger-stick whole blood. The monitoring device measures the time it takes an individual’s blood to clot. A drop of blood is obtained by a finger-stick using a lancet. The drop of blood is placed on a test strip and analyzed by the device. The device displays both the PT and calculated international normalized ratio (INR). If the results are out of normal range, the individual usually is advised to retest to confirm and if the results remain abnormal, they contact their physician as soon as possible. These devices store 30 - 60 of the most recent test results, which are date and time stamped, enabling the health care provider to review the results and monitor trends in the individual’s oral anticoagulant therapy control. 

The goal of home PT monitoring is to help the individual maintain an INR in the desired therapeutic range. International Normalized Ratio (INR) is a system established by the World Health Organization (WHO) and the International Committee on Thrombosis and Hemostasis for reporting the results of blood coagulation (clotting) tests. The INR is the ratio of the individual's prothrombin time compared to the mean prothrombin time for a group of normal individuals. The prothrombin time is the amount of time needed for a small amount of blood to clot. 

Examples of US Food and Drug Administration (FDA) approved devices for home self-monitoring PT/INR include, but may not be limited to: Alere INRatio 2 PT/INR Monitoring System; CoagCare System; CoaguChek XS System; INRatio Prothrombin Time Monitoring System; INRatio 2 Prothrombin Time Monitoring System; and ProTime Microcoagulation System. These portable testing devices are available by prescription for home use under a physician’s supervision. The physician who prescribes a home PT monitor is responsible for the training and ongoing management of individuals who use these devices. 

Alternatives to home PT monitoring include visits to a laboratory facility or health care provider’s office for drawing and testing of a venous blood sample. Physician consultation is advised to make an informed decision based on an individual’s health needs.

Home INR monitors are designed to aid in the management of high-risk patients taking oral anticoagulants.  They require considerable patient training and compliance to be useful. Self-testing and/or self-management by the patient using home international normalization ratio (INR) monitors represent another model of care with the potential for improved outcomes as well as greater convenience.  Self-testing may provide a convenient opportunity for increased frequency of testing when deemed necessary.  The use of the same instrument may increase the degree of consistency in instrumentation, and self-testing provides the potential for greater knowledge and awareness of therapy which may lead to improved compliance.  There is, however, insufficient evidence comparing the effectiveness of patient self-testing and self-management using a home INR monitor to care provided by an anticoagulation management service.  Ansell et al (2001) explained: "Although a growing number of studies indicate the superiority of patient PST [patient self-testing] or PSM [patient self-management of dose adjustments] over UC [usual care, i.e., patients managed by their usual physicians], there is little evidence comparing them to care provided by an AMS [anticoagulation management service (i.e., anticoagulation clinic)].  PST and PSM require special patient training to implement, and therapy should be managed by a knowledgeable provider.  A definitive recommendation cannot yet be made as to the overall value of PST or PSM."

In a randomized controlled trial, Gardiner and colleagues (2005) ascertained if patients can achieve accurate INR values through patient self testing (PST) by means of the CoaguChek S (Roche Diagnostics, Lewes, UK).  The main outcome measurements were comparability of INR values obtained by PST and the hospital laboratory, patient acceptability as assessed by a questionnaire and anticoagulant control.  A total of 84 subjects (53 men, 31 women; median age of 59 years), receiving long-term oral anticoagulation (warfarin), were recruited.  Subjects were randomized to weekly self-testing or continuing 4-weekly hospital laboratory monitoring of INR.  Comparison of INRs (n = 234) showed no significant differences between the CoaguChek (median INR 3.02) and laboratory testing (median INR 3.07).  There was excellent correlation between the 2 methods (r = 0.95), with 85 % of CoaguChek results within 0.5 INR units of the laboratory method.  On 4 occasions, differences of greater than 1 unit INR were obtained, but in each case the patient's anticoagulation was unstable (INR greater than 4.5 by both methods) and the differences in INR would not have altered patient management.  The results showed that 87 % of patients found self-testing straightforward, 87 % were confident in the result they obtained and 77 % preferred self-testing.  These investigators concluded that PST is a reliable alternative to hospital clinic attendance and is acceptable to the majority of suitably trained patients.

In 2002, CMS issued a national coverage determination for the use of home prothrombin time INR monitoring for anticoagulation management for patients with mechanical heart valves on warfarin.  More recently, a CMS Decision Memorandum (2008) concluded that there is sufficient evidence of the effectiveness of home prothrombin time (INR) monitoring for patients with a mechanical heart valve, chronic atrial fibrillation, or deep venous thrombosis.  The monitor and the home testing must be prescribed by a treating physician and the following requirements must be met:

  • Self-testing with the device should not occur more frequently than once a week; and
  • The patient continues to correctly use the device in the context of the management of the anticoagualtion therapy following initiation of home monitoring; and
  • The patient must have been anticoagulated for at least 3 months prior to use of the home INR devices; and
  • The patient must undergo an educational program on anticoagulation management and demonstrated the correct use of the device prior to its use in the home.

Matchar and colleagues (2010) examined the effect of home testing of INR on clinical events in patients with atrial fibrillation or mechanical heart valves.  These investigators randomly assigned 2,922 patients who were taking warfarin because of mechanical heart valves or atrial fibrillation and who were competent in the use of point-of-care INR devices to either weekly self-testing at home or monthly high-quality testing in a clinic.  The primary end point was the time to a first major event (stroke, major bleeding episode, or death).  Patients were followed for 2.0 to 4.75 years, for a total of 8,730 patient-years of follow-up.  The time to the first primary event was not significantly longer in the self-testing group than in the clinic-testing group (hazard ratio, 0.88; 95 % confidence interval [CI]: 0.75 to 1.04; p = 0.14).  The 2 groups had similar rates of clinical outcomes except that the self-testing group reported more minor bleeding episodes.  Over the entire follow-up period, the self-testing group had a small but significant improvement in the percentage of time during which the INR was within the target range (absolute difference between groups, 3.8 percentage points; p < 0.001).  At 2 years of follow-up, the self-testing group also had a small but significant improvement in patient satisfaction with anti-coagulation therapy (p = 0.002) and quality of life (p < 0.001).  The authors concluded that as compared with monthly high-quality clinic testing, weekly self-testing did not delay the time to a first stroke, major bleeding episode, or death to the extent suggested by prior studies.  These results do not support the superiority of self-testing over clinic testing in reducing the risk of stroke, major bleeding episode, and death among patients taking warfarin therapy.

Bonaros et al (2004) stated that ventricular assist device (VAD) implantation is associated with impaired primary hemostasis and thromboembolic complications.  Recently, a new generation of implantable continuous flow axial pumps was introduced into clinical application.  To study the potential thrombogenic properties of this type of pump, these researchers applied extensive platelet monitoring.  In their institution, 13 patients received the MicroMed DeBakey VAD as a bridge to transplantation.  Routine coagulation tests (platelet count, activated partial thromboplastin time, prothrombin time, anti-thrombin III activity) and platelet function tests (whole blood aggregometry, thrombelastography, flow cytometry) were performed.  No clinically relevant thromboembolic events were detected.  No correlation was found between global function tests, platelet aggregation, and thrombelastography.  No correlation was detected between platelet activation and hemolysis parameters.  Platelet aggregation and coagulation index were significantly suppressed early after operation.  A subsequent phase of hyper-aggregability, starting around day 6, suggested the initiation of anti-aggregation therapy.  Platelet activation markers were up-regulated in the post-operative period but were returned to pre-operative levels after initiation of aspirin.  In contrast to routine coagulation monitoring, platelet function tests reflect in detail the coagulation status of blood pump recipients and the efficiency of anti-aggregation therapy.  Aspirin and dipyridamole therapy in addition to oral anti-coagulation using phenprocoumon may contribute to platelet function and clot mechanics restoration and is, therefore, recommended for patients after VAD implantation.

Joshi and colleagues (2007) noted that prothrombin time, expressed as INR and activated partial thromboplastin time (aPTT), are standard methods of monitoring coumadin and heparin administration.  Prothrombin activation fragment (F1.2) is an index of in vivo thrombin generation.  These investigators hypothesized that F1.2 would provide a better surrogate of thromboembolism risk than standard coagulation assays during VAD support.  In this study, INR, PTT and F1.2 were analyzed in 31 patients after implantation of a left-sided VAD daily during hospitalization and weekly after discharge.  Thromboembolic events (TE) were defined by evidence of neurological injury revealed by plasma levels of S-100beta.  The relationships between F1.2, INR for patients on coumadin and aPTT for patients on heparin were evaluated from 1,250 observations of blood samples.  S-100beta was positively correlated with F1.2, but not with INR and aPTT.  Correlation between S-100beta and F1.2 is significantly higher than with the other 2 markers (p < 0.0001).  Higher values of aPTT and INR were not associated with TE.  Compared to conventional coagulation assays, the F1.2 level provides a single endpoint that is a more accurate predictor of TE after VAD implantation.  The authors stated that further trials that incorporate the F1.2 marker into anti-coagulation algorithms may help reduce adverse events in this high-risk population.

Baker and colleagues (2017) described the safety and efficacy of warfarin for patients with Kawasaki disease and giant coronary artery aneurysms (CAAs, greater than or equal to 8 mm).  Giant aneurysms are managed with combined anti-coagulation and anti-platelet therapies, heightening risk of bleeding complications.  These investigators reviewed the time in therapeutic range; percentage of INRs in range (%); bleeding events, clotting events; INRs greater than or equal to 6; INRs greater than or equal to 5 and less than 6; and INRs less than 1.5.  In 9 patients (5 male), median age of 14.4 years (range of 7.1 to 22.8 years), INR testing was prescribed weekly to monthly and was done by home monitor (n = 5) or laboratory (n = 3) or combined (1).  Median length of warfarin therapy was 7.2 years (2.3 to 13.3 years).  Goal INR was 2.0 to 3.0 (n = 6) or 2.5 to 3.5 (n = 3), based on CAA size and history of CAA thrombosis.  All patients were treated with aspirin; 1 was on dual anti-platelet therapy and warfarin.  The median time in therapeutic range was 59 % (37 % to 85 %), and median percentage of INRs in range was 68 % (52 % to 87 %). INR greater than 6 occurred in 3 patients (4 events); INRs greater than or equal to 5 and less than 6 in 7 patients (12 events); and INR less than 1.5 in 5 patients (28 events).  The incidence of major bleeding events and clinically relevant non-major bleeding events were each 4.3 per 100 patient-years (95 % CI: 0.9 to 12.6).  New asymptomatic coronary thrombosis was detected by imaging in 2 patients.  The authors concluded that bleeding and clotting complications are common in patients with Kawasaki disease on warfarin and aspirin, with INRs in range only 2/3 of the time.

An UpToDate review on "Coronary artery disease patients requiring combined anticoagulant and antiplatelet therapy" (Sarafoff and Holmes, 2018) states that "Patients with coronary artery disease (CAD) with indications for long-term anticoagulant and antiplatelet therapy are a clinical challenge with regard to the need to balance the benefit and risk from antithrombotic therapy.  The majority of these patients have atrial fibrillation (AF) and CAD with or without prior stenting.  In AF patients with CAD and no prior stenting, long-term treatment with an oral anticoagulant without antiplatelet therapy is recommended … For patients taking warfarin whose international normalized ratio (INR) has been relatively easy to maintain, we suggest continuing with warfarin.  For these patients taking 3 antithrombotic drugs, the INR should be monitored closely and ideally kept within the 2.0 to 2.5 range.  For patients whose INRs have been difficult to manage for reasons other than compliance or in whom the risk of bleeding is thought to be high, switching to a non-vitamin K antagonist oral anticoagulants (NOAC) is reasonable.  A patient who has difficulty having blood drawn is an example … Warfarin, when used as the anticoagulant, should be titrated to the lowest possible international normalized ratio (INR) level in patients receiving triple therapy.  One study demonstrated that aiming for a target INR of 2.0 to 2.5 leads to a significant decrease in bleeding events in patients treated with triple therapy as compared with INR levels >2.6.  The patients treated with an INR level of 2.0 to 2.5 had similar bleeding events compared with dual antiplatelet therapy (DAPT).  We recommend that the frequency of laboratory tests should be increased to safely maintain the INR levels in this lower range".

Brasen and associates (2019) noted that many patients are undergoing oral anti-coagulation treatment with vitamin K antagonists, which necessitates measuring INR several times each month.  Patients can learn to measure their INR at home and choose their own dose for the next period with potential gains in treatment quality and reduced healthcare expenses.  This is, however, connected to the potential problem of losing tight external control of the patient treatment.  These investigators performed a randomized controlled trial (RCT) using the telemedicine software CSO/AC together with the INR point-of-care-test CoaguChek XS for 10 months to investigate the use of criteria-driven healthcare interactions.  A total of 87 patients were divided into 2 groups.  The patient self-management (PSM) group was surveilled using the criteria INR less than 1.8, INR greater than 4.5, change in warfarin/week greater than 1.25 mg, missing INR or dosage.  The patient self-testing (PST) group was handled as routine care.  A total of 84 patients were followed for 10 months.  No differences were seen in average INR or fraction of INR in therapeutic range (2 to 3) in the 2 groups or the start compared with the end.  The PST group was handled using 4.2 interactions per month whereas the PSM group used 1.1 interactions per month.  No adverse effects of PSM were observed.  Using criteria-driven interactions enabled a considerable reduction in interactions per month.  The 2 groups were comparable in terms of treatment effect and safety.  The authors concluded that using criteria to guide PSM interactions maintained good treatment effect while reducing healthcare expenses.

The Medicare Decision Memorandum (2008) stated that "given that the half-life of warfarin is approximately 1.5 days and it typically requires 3-4 half-lives to reach steady state, it would not be generally necessary to test more than once a week in a patient who is beyond the initial titration period.  Therefore, we see no need to change the current nationally covered frequency limitation.  Some have noted that more frequent testing could be needed if a patient begins a new medication that may affect the metabolism of warfarin and thereby the INR.  While we do not dispute that assertion, we point out that this NCD speaks only to testing performed in the home.  If a patient’s condition has been destabilized by a change in medication or other factor, the patient may benefit from more rather than less direct attention from the treating physician".


The above policy is based on the following references:

  1. American Medical Association (AMA). Home anticoagulation monitoring. Report of the Council on Science and Public Health. Chicago, IL: AMA; 2007.
  2. Ansell J, Hirsh J, Dalen J, et al. Managing oral anticoagulant therapy. In: Sixth ACCP Conference on Antithrombotic Therapy. Chest. 2001;119:22S-38S.
  3. Baker AL, Vanderpluym C, Gauvreau KA, et al. Safety and efficacy of warfarin therapy in Kawasaki disease. J Pediatr. 2017;189:61-65.
  4. Bloomfield HE, Krause A, Greer N, et al. Meta-analysis: Effect of patient self-testing and self-management of long-term anticoagulation on major clinical outcomes. Ann Intern Med. 2011;154(7):472-482.
  5. Bonaros N, Mueller MR, Salat A, et al. Extensive coagulation monitoring in patients after implantation of the MicroMed Debakey continuous flow axial pump. ASAIO J. 2004;50(5):424-431.
  6. Bradbury MJ, Taylor G, Short P, Williams MD. A comparative study of anticoagulant control in patients on long-term warfarin using home and hospital monitoring of the international normalised ratio. Arch Dis Child. 2008;93(4):303-306.
  7. Brasen CL, Madsen JS, Parkner T, Brandslund I. Home management of warfarin treatment through a real-time supervised telemedicine solution: A randomized controlled trial. Telemed J E Health. 2019;25(2):109-115. 
  8. Brown A, Wells P, Jaffey J, et al. Point-of-care monitoring devices for long-term oral anticoagulation therapy: Clinical and cost effectiveness. Technology Report No. 72. Ottawa, ON: Canadian Agency for Drugs and Technologies in Health (CADTH); February 2007.
  9. Center for Medicare and Medicaid Services (CMS). Prothrombin time (INR) monitor for home anticoagulation management (#CAG-00087N). National Coverage Analysis (NCA). Baltimore, MD: CMS; September 18, 2001.
  10. Center for Medicare & Medicaid Services (CMS). Decision memo for prothrombin time (INR) monitor for home anticoagulation management (CAG-00087R). Baltimore, MD: CMS; March 19, 2008.
  11. Centers for Medicare & Medicaid Services (CMS). National coverage determination (NCD) for home prothrombin time/international normalized ratio (PT/INR) monitoring for anticoagulation management (190.11). Baltimore, MD: CMS; March 19, 2008.
  12. DeSantis G, Hogan-Schlientz J, Liska G, et al. STABLE results: Warfarin home monitoring achieves excellent INR control. Am J Manag Care. 2014;20(3):202-209.
  13. Dolor RJ, Ruybalid RL, Uyeda L, et al; THINRS Site Investigators. An evaluation of patient self-testing competency of prothrombin time for managing anticoagulation: pre-randomization results of VA Cooperative Study #481 -- The Home INR Study (THINRS). J Thromb Thrombolysis. 2010;30(3):263-275.
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  16. Greenway A, Ignjatovic V, Summerhayes R, et al. Point-of-care monitoring of oral anticoagulation therapy in children. Comparison of the CoaguChek XS system with venous INR and venous INR using an International Reference Thromboplastin preparation (rTF/95). Thromb Haemost. 2009;102(1):159-165.
  17. Holbrook A, Schulman S, Witt DM, et al.; American College of Chest Physicians. Evidence-based management of anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e152S-84S.
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  20. Joshi A, Magder LS, Kon Z, et al. Association between prothrombin activation fragment (F1.2), cerebral ischemia (S-100beta) and international normalized ratio (INR) in patients with ventricular assisted devices. Interact Cardiovasc Thorac Surg. 2007;6(3):323-327.
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  22. Matchar DB, Love SR, Jacobson AK, et al. The impact of frequency of patient self-testing of prothrombin time on time in target range within VA Cooperative Study #481: The Home INR Study (THINRS), a randomized, controlled trial. J Thromb Thrombolysis. 2015;40(1):17-25.
  23. National Institute for Health and Care Excellence (NICE). Atrial fibrillation and heart valve disease: Self-monitoring coagulation status using point-of-care coagulometers (the CoaguChek XS system and the INRatio2 PT/INR monitor).  NICE Diagnostics Guidance 14. London, UK: NICE; September 24, 2014.
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  25. No authors listed. Home monitoring for warfarin users. Health News. 1999;5(3):5.
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  27. Nutescu EA, Bathija S, Sharp LK, et al. Anticoagulation patient self-monitoring in the United States: Considerations for clinical practice adoption. Pharmacotherapy. 2011;31(12):1161-1174.
  28. Ontario Ministry of Health and Long-term Care, Medical Advisory Secretariat (MAS). Point-of-care international normalized ratio (INR) monitoring devices for patients on long-term oral anticoagulation therapy: An evidence-based analysis. Ontario Health Technology Assessment Series. 2009; 9(12):1-114.
  29. Plesch W, van den Besselaar AM. Validation of the international normalized ratio (INR) in a new point-of-care system designed for home monitoring of oral anticoagulation therapy. Int J Lab Hematol. 2009;31(1):20-25.
  30. Poller L, Keown M, Chauhan N, et al. European Concerted Action on Anticoagulation--comparison of fresh plasma and whole blood multicentre ISI calibrations of CoaguChek Mini and TAS PT-NC whole blood prothrombin time point-of-care monitors. Thromb Haemost. 2002;87(5):859-866.
  31. Ryan F, Byrne S, O'Shea S. Randomized controlled trial of supervised patient self-testing of warfarin therapy using an internet-based expert system. J Thromb Haemost. 2009;7(8):1284-1290.
  32. Ryan F, O'Shea S, Byrne S. The reliability of point-of-care prothrombin time testing. A comparison of CoaguChek S and XS INR measurements with hospital laboratory monitoring. Int J Lab Hematol. 2010;32(1 Pt 1):e26-e33.
  33. Sarafoff N, Holmes DR, Jr. Coronary artery disease patients requiring combined anticoagulant and antiplatelet therapy. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed November 2018.
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  35. Tripodi A. Prothrombin time international normalized ratio monitoring by self-testing. Curr Opin Hematol. 2004;11(3):141-145.
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