Monitoring

For patients treated with intravenous heparin, activated partial thromboplastin time (aPTT) or calibrated anti-Xa activity is measured:

  • Prior to heparin initiation, to obtain a baseline

  • 6 hours after initiation of the infusion

  • 6 hours after each adjustment in the dose

  • At least once daily thereafter when the therapeutic level is achieved (defined as 2 measurements in the target range without interval dose adjustment).

Target values for aPTT are based on the local laboratory's standardised aPTT values, which should correspond to a heparin level between 0.4 U/mL and 0.8 U/mL. Calibrated anti-Xa activity is an alternative to aPTT. Platelet count should be measured at baseline, then on days 3 and 5, to observe for the development of heparin-induced thrombocytopenia. Full blood count should be obtained to evaluate early signs of bleeding through decreases in haematocrit/haemoglobin.

For patients treated with low molecular weight heparin (LMWH) or fondaparinux, no therapeutic monitoring of anticoagulation is needed in most patients. Changes in patient weight may require adjustment of the dose. Renal function indices, such as serum creatinine and urea, should be obtained to determine initial and ongoing appropriateness of LMWH and fondaparinux as both require discontinuation or dose adjustment in renal impairment.

Frequent international normalised ratio (INR) monitoring of patients who are treated with warfarin is required. This is preferably done by experts or specialised anticoagulation clinics, whenever possible. Anticoagulant therapy, although potentially life-saving, has inherent bleeding risks. A systematic approach will reduce the likelihood of adverse events.[158] In the UK, patients can self-monitor their INR using portable point-of-care instruments; this is used by the anticoagulation clinic to inform dosing.[159]

The initial dose and titration of warfarin is more efficient and leads to better patient outcomes if an estimating equation is used, rather than a fixed-dose initiation algorithm.[113][114]

Rivaroxaban, apixaban, edoxaban, and dabigatran do not require laboratory monitoring for anticoagulant effect. It is recommended that attention be directed to any changes in renal or liver function testing as clinically indicated (e.g., at baseline then as indicated). With direct oral anticoagulants (DOACs), any changes in concomitant interacting medications (addition or discontinuation) should also be closely monitored because this may require dose adjustment or discontinuation of the current DOAC, or a change to an alternative anticoagulant.

Patients should be assessed for the development of post-thrombotic syndrome; this is under-recognised in practice. In addition, patients who have pulmonary embolism should be evaluated clinically over time to determine whether they have chronic thromboembolic pulmonary hypertension due to unresolved pulmonary emboli, which may occur in up to 4% of patients.[160]

Use of this content is subject to our disclaimer