Urinary excretion of pyridinium cross-links in healthy adults and patients with MGUS, MM, and osteoporosis. Patients with smoldering myeloma (•) are included in the MGUS section. MM I + II, MM patients with stage I (•) and stage II (○) disease; MM III, MM patients with stage III disease. (——) Median; (⋅⋅⋅⋅⋅) upper limit of normal range.