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

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).

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.

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.

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.