Can a blood test for 'lymphocyte surface markers' rule out lymphoma? or is biopsy truly the only way?

Biopsy is best: If lymphoma cells are circulating in the bloodstream, they might be able to be identified by flow cytometry (which is a test for lymphocyte surface markers). However, the most reliable method would be to perform a biopsy of any enlarged lymph node. Plus, if there is lymphoma, there are important aspects of a biopsy diagnosis that cannot be derived using a blood test.