Is the measurement of copper and iron in liver biopsies reliable? Results from a pilot external quality assurance scheme.

The determination of copper and iron in liver biopsies have important roles in the diagnosis of Wilson's Disease and haemochromatosis respectively. An external quality assurance scheme is essential for analytical validation of results, however, none was available for these analytes at the time of this investigation. Accordingly a pilot scheme was established. The results of this scheme and of a corresponding questionnaire are recorded. Twenty-nine identical sets of lyophilised certified reference materials or dried aliquots of livers purchased from local stores were distributed to 26 specialist trace element laboratories offering this clinical service. Using results returned, target values were assigned and analytical imprecision and accuracy were assessed. Laboratories were also asked to complete a questionnaire regarding details of sample preparation, analytical method and interpretation. Accuracy was worse than ± 50% at least one result in 38% of laboratories measuring copper and 57% measuring iron. Within-batch imprecisions poorer than ± 50% were found in 20% and 23% of liver copper and iron results respectively. Accuracy was found to be statistically poorer if sample weights less than 3 mg were measured. Reference ranges were frequently absent from reports or disagreed with international guidelines. A significant proportion of laboratories are unable to provide consistently reliable analytical performance to the extent that misdiagnosis may occur. The current diagnostic service is further compromised by the lack, or unreliability, of appropriate reference ranges provided on reports making interpretation more difficult. Without improvement, a review of current guidelines may be necessary.