Reference Range for Prothrombin Time-Coumadin

The optimal therapeutic ranges for the International Normalized Ratio (INR) for patients on oral anticoagulant therapy, according to the American College of Chest Physicians and the National Heart, Lung and Blood Institute (CHEST, volume 126 [supplement], page 204S, 2004), are shown below:

Indication                                                                                            INR

Post-surgical Prophylaxis of venous thromboembolism

(high-risk surgery)                                                                 2.0 - 3.0

Treatment of venous thrombosis                                               2.0 - 3.0

Treatment of pulmonary embolism                                             2.0 - 3.0

Secondary Prevention

Tissue heart valves                                                       2.0 - 3.0

Acute myocardial infarction (to prevent systemic embolism)  3.0 - 4.0

Valvular heartdisease                                                     2.0 - 3.0

Atrial Fibrillation                                                            2.0 - 3.0

Mechanical prosthetic valves (high risk)                                       2.5 - 3.5

Myocardial infarction (prevention of recurrence)                            1.3 - 1.8


Note:  The INR is intended for use only for monitoring the degree of anticoagulation in patients receiving oral coumarin derivates; most commonly Coumadin (warfarin).

Therapeutic LMWH Ranges

The optimal therapeutic ranges for LMWH will vary according to the drug. The measured peak anti-Xa activity varies among individual LMWH preparation given in the same anti-Xa dose due to variation in pharmacokinetics. The antiXa activity peaks at approximately 4 hours and this is the recommended time to perform monitoring assays if possible. Conservative therapeutic guidelines according to the American College of Chest Physidcians and the National Heart, Lung and Blood Institute (CHEST, volume 126 [supplement], page 204S, 2004) are shown below:

Enoxaparin (twice daily dosing for VTE)                         0.6 - 1.0 anti-Xa units

Enoxaprain (once daily dosing for VTE)                          Not established

Tinzaparin (once a day)                                              0.85 mean anti-Xa units

Dalteparin (once a day)                                              1.05 mean anti-Xa units

Fonaparinux (once a day)                                            Not established

Note: Pediatric dosing may be different than that for adults but data are lacking.

Therapeutic Direct Thrombin Inhibitors (DTI) Ranges

The optimal therapeutic ranges for the DTIs have not been established. Package insert therapeutic guideline suggests 1.5 - 3.0 times the baseline PTT.