NCC has not been validated as a reliable biomarker of WD treatment due to the fact that the current method for NCC calculation is indirect (calculated from the difference between the copper concentrations in μg/dL and 3.15 times the serum Cp concentration in mg/dL) and may give non-diagnostic false negative results in up to 20% of patients, particularly when immunological methods of Cp assessment are used due to overestimation of holoceruloplasmin. Here, CP is linked to Wilson disease.