Anticoagulant monitoring

Keywords: Oral anticoagulant therapy

Types of anticoagulant

Appropriate Tests


See also Thrombolytic therapy (Thrombolysis).

The type of tests and frequency of testing depends on the anticoagulant therapy and indication, as well as clinical history.

Heparin (standard, unfractionated)

Prior to commencing Full blood count (including platelet count), Coagulation profile (including APTT, INR, Prothrombin time). Platelet count is recommended on day 5 post commencement of therapy.

The method for monitoring continuous IV heparin infusion is usually APTT, however Activated clotting time (ACT) and Anti factor Xa are also used.

The level of anticoagulation may be monitored with the APTT and/or Anti factor Xa level, however monitoring(including the test and frequency) should be according to local guidelines. Prophylactic (low dose) heparin does not usually require monitoring.

In the event of bleeding on heparin, urgent APTT and Full blood count should be performed. 

If progression of thrombosis, or thrombosis in other site(s) while patient on heparin, causes include:

  • Inadequate anticoagulation
  • Heparin-induced thrombocytopenia (HIT type II)
  • Antithrombin deficiency

APTT, Anti factor Xa

See also Heparin-induced thrombocytopenia investigation

Antithrombin - ideally should be deferred until heparin has been ceased (if not performed for some reason prior to heparin therapy), since heparin will reduce the measured level. Consultation with a haematologist is recommended to guide further testing and management. See also Thrombosis - venous.

Low molecular weight heparin (LMWH) and heparinoids

Prior to commencing, Full blood count (including platelet count), Coagulation profile (including APTT, INR, Prothrombin time) and renal function should be performed. Platelet count is recommended on day 5 post commencement of therapy.

Monitoring of (full dose) low molecular weight heparin (LMWH) therapy is not generally required, except in renal failure, extremes of body weight, pregnancy or other situations where there is an increased risk of bleeding. LMWH should be used with care and monitoring in patients with any abnormality of renal function, particularly the elderly. Monitoring is with an Anti factor Xa level, but should be done in consultation with a haematologist and according to local guidelines.

Monitoring of routine LMWH prophylaxis is not cost effective, is not required to achieve clinical efficacy and is not indicated to predict risk of bleeding, which is minimal with prophylactic doses in patients with normal renal function.

Oral anticoagulants


  • Warfarin (Marevan/Coumadin)

Prothrombin time, INR

Increased frequency of testing may be required following change in dose, change in diet/oral intake, intercurrent illness and change in concomitant medications (including antibiotics).

For information on reversal of warfarin, see guidelines below.

  • New oral anticoagulants (NOACS)

NOAC do not require monitoring when used for thromboprophylaxis or therapeutic anticoagulation.

However, the anticoagulant effect should be measured if:

1. Clinically significant bleeding occurs
2. There is a change in clinical circumstances (eg, urgent surgery is required)

Routine coagulation studies may (but sometimes do not) provide information about the presence of anticoagulant effect (see below).

Specific assays for quantitation of drug levels may or may not be available depending on the drug and laboratory. Due to the short half-life of these drugs, information on the time of the last dose is important in interpreting the results.

 Refer to coagulation laboratory.

  • Dabigatran

The Thrombin time (TT) is the most sensitive routine coagulation assay to detect the presence of dabigatran. A normal TT excludes the presence of dabigatran, however low drug levels may significantly prolong the TT, therefore the assay cannot be used to estimate plasma levels.

Some laboratories may perform a drug level assay (dilute thrombin clotting time assay).

  • Rivaroxaban

The Prothrombin time, INR (using a thromboplastin that is sensitive to rivaroxaban) is the most sensitive routine coagulation assay, however a normal PT does not exclude its presence. The APTT and PT cannot estimate the intensity of anticoagulant effect

Some laboratories may provide a drug specific anti-Xa for quantitative assessement of drug plasma levels. The clinical relevance of drug plasma levels is not known, and therefore should not be used to inform drug doses.

A normal PT and APTT does not exclude significant anticoagulant effect.

Drug specific anti-Xa assay may be used to estimate drug plasma levels, but this is not yet widely available. Please consult with laboratory.


Garcia DA et al; American College of Chest Physicians. Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis. 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141 (2 Suppl): e24S-43S.

Tran H et al. An update of consensus guidelines for warfarin reversal. MJA 2013; 198: 198-199.

Tran H et al. New oral anticoagulants: a practical guide on prescription, laboratory testing and peri-procedural/bleeding management. IMJ 2014; 44: 525-536.

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