What Is Anticoagulant Therapy Monitoring?

Anticoagulant therapy is the use of anticoagulant medications to reduce the risk of unwanted blood clots. There are several types of anticoagulants, but each is designed to block the formation of clots where they pose a threat to health or to break down clots that have formed inappropriately.

Physicians utilize anticoagulants to decrease the likelihood of strokes, heart attacks, and pulmonary embolisms. Anticoagulants also protect patients with medical conditions that increase their level of exposure, including atrial fibrillation, clotting disorders, and heart-valve disease and replacements.

Anticoagulant therapy requires monitoring. This is to ensure that the levels of medication meet a targeted range of values for measuring clotting factors. Warfarin and its brand-name equivalents are the primary drugs in this category, along with the unfractionated version of heparin. Tests are being deployed for the newer medications as well.

If you or a loved one is concerned about blood clots – for example, you have a family history of strokes or heart disease – schedule a visit with a provider in the Baptist Health medical network.

Types of Anticoagulants

Anticoagulants work in different ways but share the goal of reducing blood clots in persons for whom clotting poses a heightened health risk. The major anticoagulants include:

• Warfarin and brand-name equivalents: Warfarin is a commonly used anticoagulant derived from a chemical compound found in numerous plants. It is a vitamin K antagonist, meaning that it interferes with vitamin K’s role in the clotting process. Warfarin comes in pill form and is sold under the brand names Coumarin and Jantoven. Dosage is one pill daily.
• Direct oral anticoagulants (DOACs): DOACs are a newer generation of anticoagulants also in pill form. Dabigatran inhibits the activity of thrombin, an enzyme critical to the clotting process. The other DOACs, including apixaban, betrixaban, and edoxaban, perform a similar role for factor Xa, another clotting agent. Dosage is one or two pills daily. Taking these pills on a regular schedule enhances their effectiveness.
• Heparin and derivatives: Heparin is one of the oldest available anticoagulants. It works differently from the previous medications, increasing the activity of natural anticlotting factors in the blood, rather than interfering directly with the clotting process. Heparin is an injectable medication and comes in two versions, unfractionated (UFH) and low-molecular-weight (LMWH). UFH is delivered intravenously, LMWH by subcutaneous injection (shots). The latter is longer lasting and more predictable in dosage. A third drug, fondaparinux, is a synthetic equivalent to heparin.
• Direct thrombin inhibitors (DTIs): DTIs are injectable alternatives to heparin. Like the oral anticoagulants, these medications directly intervene in the clotting process. Included in this category are argatroban, bivalirudin, and desirudin.

How to Monitor Anticoagulant Therapy

The human body relies on a complex system of clotting and anticlotting factors to control when and where coagulation occurs. Clotting is required for cuts, scrapes, wounds, and ulcers to protect us from blood loss. On the other hand, if clots form too readily, blocking otherwise healthy veins or arteries, or detach from vessel walls and circulate through the body, they pose a variety of health risks, including the possibility of causing strokes or myocardial infarctions (heart attacks).

The goal of anticoagulant therapy is to assist the body in properly balancing clotting and anticlotting factors. This is why monitoring the therapy is critical to its success. Supporting the clotting process requires that dosages remain within certain effective ranges. Depending on the medication, falling outside the range can mean either an increased likelihood of clot formation or a greater tendency to internal bleeding or excessive blood loss.

Monitoring occurs by means of bloodwork. Most analysis takes place in a medical lab. However, home testing kits are now available for certain measures, including the International Normalized Ratio (INR), which is used with warfarin.

Different Methods of Monitoring

Medical science has developed several measures for monitoring the effectiveness of anticoagulant therapy:

• International Normalized Ratio (INR): The INR is a standardized test for assessing warfarin’s impact on the body. It measures a person’s clotting tendency in comparison to a control group. Patients who are new to this medication must be tested frequently, weekly at least, until targeted rates are achieved. The frequency of testing decreases with time.
• Activated Partial Thromboplastin Time (aPTT): Activated PTT is a second means of determining the efficacy of an anticoagulant medication, in this case heparin, especially the fractionated version. Activated PTT measures the speed of clotting. Heparin requires continual monitoring when first administered, until the therapeutic target is met.
• Anti-factor Xa: Anti-factor Xa is a third method for monitoring anticoagulant medications. It is being used with both heparin, especially the LMWH version, and the newer class of direct oral anticoagulants (the DOACs). Patients on DOAC therapy require less monitoring than either warfarin or heparin, with an initial test at one month and then every three months going forward.

Each of these measures focuses on clotting rates, with reference to a different aspect of the chemical process.

Interpreting Test Results

Anticoagulant tests are interpreted in the following manner:

• International Normalized Ratio (INR): The INR is stated as a number in the low single digits. The therapeutic range for most persons on warfarin is between 2.0 and 3.0. If your number is below 2.0, your risk of blood clots is relatively high. If your number is above 3.0, your risk of bleeding increases accordingly.
• Activated Partial Thromboplastin Time (aPTT): The results of an activated PTT test are given in seconds. A typical value is in the range of 30 to 40 seconds. A person on heparin should expect a value of 60 to 80 seconds. Results above or below that could indicate a bleeding problem, liver dysfunction, or some other medical issue.
• Anti-factor Xa: Anti-factor Xa results are stated as a ratio of heparin sodium (IU) to milliliters (mL). The therapeutic range for unfractionated heparin is 0.3 to 0.7 IU/mL and for LMWH is 0.5 to 1.2 IU/mL. Results outside of these ranges may indicate greater tendencies for clotting or bleeding.

Factors Affecting Test Results

Variations in the type, timing, and regularity of anticoagulant use can impact the results of testing. Certain preexisting medical conditions may also play a role, along with food and drug interactions. Anticoagulant usage can also affect testing for other conditions not directly related to clotting management.

What Precautions Should Be Taken When Monitoring Anticoagulants?

Oral anticoagulants have been linked on occasion to adverse reactions, especially in older patients. Care should be taken that test results fall within therapeutic ranges to avoid complications such as bleeding in the elderly.

Learn More About Anticoagulant Therapy Monitoring

Anticoagulant therapy is an important tool for physicians managing the risk of strokes, heart attacks, and other health threats in patients subject to blood clots. Several anticoagulant therapies are available with a range of cost-and-benefit tradeoffs. Monitoring the use of these medications is one key to their effectiveness.

If your family history makes blood clots a concern, schedule a visit to your Baptist Health primary care physician or specialist.