Several different international and national reference materials for plasma proteins have been in use world-wide since the mid 1970's. Most important were the WHO international reference preparations for serum immunoglobulins and for six other human serum proteins and the First United States National Reference Preparation for Specific Human Serum Proteins. These standards had values assigned to them in International Units but mass units were subsequently assigned by several methods against a number of different primary materials. Despite their existence quality control surveys in Europe and the USA in the late 1980's showed that values for a number of proteins varied by as much as 50 to 100 per cent, depending on the reference material used. In order to address these issues a new international reference material for plasma proteins has been produced and certified by BCR; BCR CRM 470 with values certified for 14 plasma proteins
To assign values to CRM 470 for the acute phase protein, 1-antichymotrypsin (ACT) and for kappa (K) and lambda (L) light chains of the immunoglobulins. Measurements of these proteins are increasing in importance for the diagnosis and management of disease and no international reference materials exist for them.
The purified preparations of ACT showed similar results though these were significantly different and could not be merged. The recombinant material showed a marked difference in immunoreactivity, possibly due to the absence of carbohydrate side chains. The values derived from the preparation with the greatest purity and physicochemical similarity to the protein present in CRM470 were used. The values obtained from the different approaches for the certification of light chains differed markedly. Pooled monoclonal light chains provided a higher ascribed value than light chains derived from polyclonal immunoglobulins and the values differed from those obtained by calculation on the basis of the ascribed values for IgG, IgA and IgM. The values obtained by RID differed from those of nephelometry and turbidimetry. Thus values for light chains were not certified and purified light chains whether monoclonal or polyclonal were deemed unsuitable to assign accurate values for light chains bound to immunoglobulins. The certified ACT mass concentration is 0.245 ( 0.015 g/L.
The use of CRM 470 world-wide for serum protein analysis has already resulted in a demonstrable improvement between laboratories and kits. In particular quality control schemes in various European countries have shown a considerable improvement in the results of analysis of many of the 14 proteins since the introduction of CRM 470. ACT values are currently being adopted by manufacturers of diagnostic kits worldwide.
Purified K and L immunoglobulin light chains were produced by the reduction of intact immunoglobulin molecules from human serum by DAKO, and from a pool of monoclonal light chains derived from human urine by Scipac. Purified ACT from human serum was produced by Behringwerke and Scipac by different techniques and the University of Leeds synthesised recombinant ACT in E.coli from the human gene. Values were assigned to BCR CRM 470 by a certification campaign in 5 laboratories, Behringwerke, two laboratories in DAKO, Lyon and Sheffield.
Funding SchemeCSC - Cost-sharing contracts
ME9 8AQ Sittingbourne