Development and preparation of a new serum protein reference material: feasibility studies and processing.

BACKGROUND: The availability of matrix reference materials is essential for the standardisation of (immuno)assays used to measure proteins. The reference material ERM-DA470 (previously called CRM470) certified in 1993 has led to a large degree of harmonisation of these assays. A new serum protein reference material has now been produced (ERM-DA470k). It is intended to replace ERM-DA470, and will additionally be certified for beta(2)-microglobulin (B2M). METHODS: Serum from 390 healthy donors was pooled and processed so as to stabilise, delipidate and 'maturate' it. Purified C-reactive protein (CRP) and recombinant B2M were added. Pilot batches were produced to study the stability, homogeneity, and commutability of the material. On the basis of the results with the trial batches it was decided to proceed with the processing of the main batch of a candidate reference material. RESULTS: Two pilot batches were produced and the processed and spiked serum lyophilised after filling (1 mL). The B2M in the material was shown to be stable and commutable. For CRP, it was discovered that freeze-drying led to a decrease in measurable protein. The main batch of candidate reference material was produced and fulfilled the required criteria in terms of optical transparency, homogeneity and stability. CONCLUSIONS: A new serum protein reference material has been produced with the properties required for a serum protein reference material for 14 proteins. An apparent loss of CRP of approximately 20% was observed upon freeze-drying of the material.

Quality assurance for cerebrospinal fluid protein analysis: international consensus by an Internet-based group discussion.

A group of neurologists and clinical neurochemists representing twelve countries worked towards a consensus on laboratory techniques to improve the quality of analysis and interpretation of cerebrospinal fluid (CSF) proteins. Consensus was approached via a virtual Lotus Notes-based TeamRoom. This new approach respecting multicultural differences, common views, and minority opinions, is available in http://www.teamspace.net/ CSF, presenting the implicit, complementary version of this explicit, printed consensus. Three key recommendations were made: CSF and (appropriately diluted) serum samples should be analyzed together in one analytical run, i.e., with reference to the same calibration curve. Results are evaluated as CSF/serum quotients, taking into account the non-linear, hyperbolic relation between immunoglobulin (Ig)- and albumin-quotients rather than using the linear IgG index or IgG synthesis rate. Controls should include materials with values within the reference ranges (IgM: 0.5-1.5 mg/l; IgA: 1-3 mg/l; IgG: 10-30 mg/l and albumin: 100-300 mg/l). The physiological, methodological and clinical significance of CSF/serum quotients is reviewed. We confirmed the previous consensus on oligoclonal IgG, in particular the usefulness of the five typical interpretation patterns. The group compared current external and internal quality assurance schemes and encouraged all members to maintain national or local traditions. Values for acceptable imprecision in the CSF quality assurance are proposed.