The present invention relates generally to diagnostic methods, systems, assays and kits for identification of subjects with cardiac amyloid deposits, where a low level of clusterin protein in a peripheral fluid sample, e.g., a serum sample from the subject, indicates the subject likely has cardiac amyloid deposits. Other aspects relate to methods of treatment of diseases or disorders characterized by cardiac amyloid deposits and transthyretin (TTR) amyloidosis, and more particularly to methods of treatment of cardiac-related amyloidosis and cardiac amyloid deposits in subjects with familial transthyretin (TTR), senile systemic amyloidosis (SSA), or familial amyloidodic polyneuropathy (FAP), or immunoglobulin light chain (AL) amyloidosis. Other aspects relate to methods and compositions comprising clusterin (CLU) or a clusterin agent (e.g. an agonist of clusterin activity or a biologically active fragment or derivative thereof), and their use in methods to treat a disease or disorder characterized by transthyretin (TTR) amyloidosis, e.g. senile systemic amyloidosis (SSA) or familial amyloidodic polyneuropathy (FAP), and their use in methods to treat amyloidotic cardiomyopathy associated with transthyretin (TTR) amyloidosis.