Went to the doctors for fast heart rate yesterday, they did blood tests and it showed my d dimer was 1.50 so they did ct scan for blood clots and the results were negative for blood clots. what else can cause d dimer to be high?

D-dimer is more useful in excluding blood clots. A level of 1.5 may or may not be high depending on the reference range of the laboratory that did the test. There are many causes of elevated d-dimer, eg., inflammation, trauma, pregnancy etc. Talk to the doctor who ordered the test and knows more about your health! Wish you good health!

Would suggest trying to find out the source for your main symptom, tachycardia or fast heart rate. Your D -dimer was minimally elevated and a variety of inflammatory conditions, including more or less recent infections can cause such changes. Follow up will be needed with your primary care doc that can clarify and prioritize.