Non-ceruloplasmin-bound copper in routine clinical practice in different laboratories.
BACKGROUND
Copper is an essential nutrient but is toxic when the free form is in excess. Wilson's disease (WD) is an autosomal recessive disorder of copper excess. Its diagnosis is a challenge, especially in the absence of obvious neurological changes, or Kayser-Fleischer rings. Non-ceruloplasmin-bound copper is a calculated parameter devised for the investigation of patients who potentially have WD.


METHODS
We compared non-ceruloplasmin-bound copper from three different laboratories. We retrospectively reviewed paired ceruloplasmin and copper data and calculated non-ceruloplasmin-bound copper. Comparative statistics, linear regression, chi-square test and graphical techniques were employed to compare the data.


RESULTS
All three assays had negative results for over 20% of the non-ceruloplasmin-bound copper concentrations; this was not significantly different. However, there were statistically significant differences for the 97.5th percentile. When plotted against the ceruloplasmin and copper concentrations, significant differences existed for both the visual and linear regression data between the three different laboratories.


CONCLUSIONS
Non-ceruloplasmin-bound copper cut-offs may not be transferable between laboratories. Each laboratory should derive its own cut-offs for the 97.5th percentile, as there are differences due to assays, populations or both.
Twomey
Patrick J
PJ
Department of Clinical Biochemistry, The Ipswich Hospital, Ipswich IP4 5PD, UK. ptwomey@nhs.net
Viljoen
Adie
A
Reynolds
Timothy M
TM
Wierzbicki
Anthony S
AS
D002570:Ceruloplasmin / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D019411:Clinical Laboratory Techniques; D003300:Copper / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D006527:Hepatolenticular Degeneration / Q000175:diagnosis*; D006801:Humans; D011237:Predictive Value of Tests; D012189:Retrospective Studies
D003300:Copper; D002570:Ceruloplasmin