Millions of Americans take aspirin every day in hopes of preventing a heart attack or a stroke.Studies have shown that for 25 percent of those patients, aspirin is not working. They are what the medical community calls aspirin resistant.Earlier this month, an article published in the American Heart Associations journal, "Circulation," confirmed that resistance to aspirin could lead to an increased risk of heart attack, stroke and cardiac death.It was based on a sub-study of the Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management and Avoidance (CHARISMA) trial."We just sort of arrived at a figure that a baby aspirin a day would work. And, for some people we now know that is not true. They have aspirin resistance," said Dr. Richard Collins.Collins is a cardiologist at South Denver Cardiology. Hes certain of aspirins benefits but knows each of his patients needs an individualized dosage."Aspirin is a double-edged sword. It prevents clots from happening inside the arteries, but it also causes bleeding outside of the tissues. So, it's not a simple drug that you just pop and say, 'Oh the side effects are minimal,'" said Collins.Collins now recommends the AspirinWorks test to his patients who take aspirin.You need to take the correct dose. We have tests available to make it safer for you. We now have something to focus individually, said Collins.The AspirinWorks test was developed in Broomfield by Corgenix Medical Corporation. It is the only FDA-cleared test for measuring aspirins effectiveness.Aspirin works by preventing the production of a molecule called thromboxane, a naturally produced chemical that causes platelets to stick together and clot. Our test is a simple test that measures thromboxane in urine, said Jon Geske, a project director at Corgenix."A lot of other things do negate aspirin effects such as supplements and other drugs such as ibuprofen," said Collins.With the AspirinWorks test, Collins is confident he can find the right combination of therapy and dosage for every patient.For more information, visit AspirinWorks.For more information, visit Circulation Journal.