What Is a D-Dimer Test? Its Purpose, Procedure & what a positive result means. A D-dimer test is a blood test that checks for, or monitors, blood-clotting problems. A positive test means the D-dimer level in the body is higher than normal and suggests someone might have blood clots. This test measures the amount of D-dimer, a type of protein the body produces to break down a blood clot. Dr. Mohammed Umeer (MBBS, DNB /specialist Family Medicine – Ahalia hospital Abu Dhabi) discusses the significance of the D-Dimer Test.