Both existing clinical criteria and genetic testing have significant limitations for the diagnosis of Wilson’s Disease (WD) often creating ambiguities in patient identification leading to delayed diagnosis and ineffective management. ATP7B protein concentration, indicated by direct measurement of surrogate peptides from patient dried blood spot (DBS) samples, could provide primary evidence of WD. ATP7B concentrations were measured in patient samples from diverse backgrounds, diagnostic potential is determined, and results are compared to biochemical and genetic results from individual patients.