WHY DO IMMUNOASSAYS FOR TUMOR-MARKERS GIVE DIFFERING RESULTS - A VIEWFROM THE UK NATIONAL EXTERNAL QUALITY ASSESSMENT SCHEMES

External Quality Assessment schemes can provide unique insight into ho w current methods are performing in the field. Results from the UK Nat ional External Quality Assessment Schemes, which monitor performance o f immunoassays for a number of tumour markers and peptide hormones in serum, show that in spite of considerable improvements resulting from increased assay automation, major discrepancies in results obtained ar e still observed. Reasons for this include poor calibration, use of an tibodies of differing specificity, and vulnerability to clinically rel evant interferences. Variation in quoted reference ranges is also a ca use of concern. Each of these important aspects of performance will re quire attention if improved between-method and between-laboratory agre ement is to be achieved.