NOACs: Why Isn’t There a Way to Measure Their Effectiveness?
Warfarin has one, but the NOACs don’t. What am I talking about?
Warfarin (Coumadin) has a way to monitor and measure its effectiveness for a specific patient. But there’s no similar way to measure the effectiveness of the new Novel Anticoagulant drugs (NOACs).
Warfarin and Your INR
With warfarin, blood testing for your INR (International Normalized Ratio) will tell your doctor what dosage of warfarin is needed to maintain your ideal INR range between 2.0 and 3.0. (Below 2.0, there’s more of a risk of an ischemic [clotting] stroke; above 4.0, there’s more of a risk of a hemorrhagic [bleeding] stroke.)
NOACs: No Blood Testing but at What Price?
From the clinical trials we know NOACs work as well as warfarin. In addition, the NOACs don’t require periodic blood testing. But the FDA, under pressure for new anticoagulants, approved the NOACs without there being any established or universally recognized method of determining their clot preventing effectiveness.
Without any method of determining their clot preventing effectiveness, how can you determine if your NOAC is working for you?
How Much NOAC is Actually Working in Your Blood?
More bad news: not all of your NOAC may actually be working for you. Pradaxa, for example, is 80% cleared by the kidneys. This means there may be lower anticoagulant levels in your blood stream, and a lot of your clot prevention is being flushed away by your kidneys. (Eliquis, Xarelto and Savaysa fare better with only 25%, 33% and 35% being cleared by the kidneys, respectively.)
What matters, though, is how much protection you are getting from your NOAC.
Blood Viscosity to Measure Anticoagulant Effectiveness?
Blood viscosity may be the answer for now. Viscosity is a measurement of the thickness and stickiness of a person’s blood. Impaired viscosity or blood flow is associated with most risk factors for cardiovascular disease.
Unfortunately there isn’t a standardized, universally recognized test for blood viscosity. (When you get your annual physical, you will seldom see a test for blood viscosity.)
However, certain factors affect blood viscosity. Could these factors be a way of inferring the effectiveness of NOACs (and natural blood thinners)?
Here are the four primary factors of blood viscosity:
1. Hematocrit. The greater number of blood cells one has, the thicker one’s blood is going to be. Hematocrit is considered responsible for 50% of the total contribution of these four factors to blood viscosity. The standard measurement is 45%. The range is 40.0–50.0%. (I take the supplement Nattokinase and have a hematocrit of 43.1%.)
2. Red blood cell (RBC) deformability. This refers to the ability of RBCs to bend and fold themselves in order to make their way through the slender passageways of the capillaries. It’s considered the second most important determinant of blood viscosity. New RBCs are better able to bend and fold into the capillaries. Regular blood donors and women in their childbearing years have more new RBCs. (ex: I give blood every 8 weeks.)
3. Plasma viscosity. Hydration usually determines this factor. Young male athletes who sweat a lot have greater risks of poor blood viscosity. (If you are properly hydrated, your urine should be light or straw-colored.)
4. RBC sedimentation/aggregation. This is the tendency of RBCs to be attracted to each other and ‘stick together’. In a standard blood test, the number of platelets might give an indication of RBC sedimentation/aggregation. (A normal range is 150-450. My platelet count is 162.)
Other Indicators of Blood Viscosity
In other tests, people with more viscous blood also had more fibrinogen, total serum protein and triglycerides concentration, while people with higher levels of HDL cholesterol had less viscous blood.
What this Means to Patients on NOACs
If you’re an A-Fib patient (or anyone) taking one of the new anticoagulants, discuss this article with your doctor (take a copy to your appointment). Talk about wanting to verify that the NOAC you are taking is effective in protecting you from the increased risk of clots and A-Fib stroke.
Perhaps your doctor can infer the effectiveness of your NOAC by checking your blood viscosity using one or more of these factors affecting viscosity.
• Hematocrit (most important)
• Platelet count
• Total serum protein
• Triglycerides concentration
• HDL cholesterol
Remember, what matters is not the clinical study results. What is important is how much protection you are getting from your NOAC.