Is use of d-dimer a waste of time and resources to rule out a clot for someone with polycythemia vera?

Nonspecific test: D dimmers have a good negative predictive value which means that if it is normal, a clot can essentially be ruled out. However, it is a very non-specific test which means that being abnormal doesn't mean that a patient has a clot. So one should consider the pretext possibility (such as symptoms)of having a clot before sending the test and then interpreting the results of a D dimer test.

No: D-dimers when used in conjunction with clinical history and possible imaging is a screening test for "clots".