Background: The relationship between serum 'free' copper and urine copper in patients with Wilson disease has not been explored.
Aim: The object of this study is to ascertain if there is a direct relationship between these two parameters.
Method: The case notes of 320 patients with Wilson disease, seen between 1960 and 1987, have been reviewed. Eighty of these patients had received no treatment before referral and the results of serum 'free' copper and urine copper on admission and at one year of treatment have been analysed.
Results: Except for patients with acute haemolysis, the ratio between 'free' serum copper and urine copper before treatment, on average, is around 7:1, after treatment this falls to around 5:1. But results show a wide scatter and there is no direct linear relationship.
Conclusion: The term 'free' copper is misleading and should be replaced by the more cumbersome but accurate term 'noncaeruloplasmin bound copper'. Most 'free' copper is complexed to albumin and is only available for excretion if there is significant protein loss by the kidneys.