Q:  What is the most common cause of "false-negative" D-Dimer test?

Answer:  inappropriate collection of specimen

D-Dimer test may give "false-negative" result if the specimen collection tube is not sufficiently filled (undefiled). This is due to the dilutional effect of the anticoagulant. The blood should be collected in a 9:1 blood to anticoagulant ratio, in specimen tube.