Protein standardization II: Dry mass determination procedure for the determination of the dry mass of a pure protein preparation

Extraction, isolation, and concentration of calprotectin antigen (S100A8/S100A9) from granulocytes

BACKGROUND

Calprotectin is a promising biomarker for granulocyte activation. It is mainly measured in faeces as a marker for inflammatory bowel disease. A limitation is that there is no widely accepted calibrator.

AIM

To establish a method for purification of calprotectin from human granulocytes that is easily reproducible, reliable, and could contribute to a better agreement between different calprotectin methods.

METHODS AND RESULTS

Calprotectin was purified from granulocyte extracts using ion-exchange chromatography. The granulocytes were separated from blood bags. The purity was analysed by analysing pixel density of a picture of the sodium dodecyl sulfate polyacrylamide gel electrophoresis and by size exclusion chromatography. The calprotectin concentration of the pure antigen solution was determined using Biuret method. The purity was >95% for 3 preparations, and their concentrations were 1079, 1080, and 1813 mg/L.

CONCLUSION

It is possible to reproducibly prepare highly purified calprotectin antigen from human granulocytes. The preparations can be used for preparing calibrators, controls for immunological calprotectin assays, and immunisation for raising antibodies against human calprotectin in hens.

Harmonization: the sample, the measurement, and the report

Harmonization of clinical laboratory results means that results are comparable irrespective of the measurement procedure used and where or when a measurement was made. Harmonization of test results includes consideration of pre-analytical, analytical, and post-analytical aspects. Progress has been made in each of these aspects, but there is currently poor coordination of the effort among different professional organizations in different countries. Pre-analytical considerations include terminology for the order, instructions for preparation of the patient, collection of the samples, and handling and transportation of the samples to the laboratory. Key analytical considerations include calibration traceability to a reference system, commutability of reference materials used in a traceability scheme, and specificity of the measurement of the biomolecule of interest. International organizations addressing harmonization include the International Federation for Clinical Chemistry and Laboratory Medicine, the World Health Organization, and the recently formed International Consortium for Harmonization of Clinical Laboratory Results (ICHCLR). The ICHCLR will provide a prioritization process for measurands and a service to coordinate global harmonization activities to avoid duplication of effort. Post-analytical considerations include nomenclature, units, significant figures, and reference intervals or decision values for results. Harmonization in all of these areas is necessary for optimal laboratory service. This review summarizes the status of harmonization in each of these areas and describes activities underway to achieve the goal of fully harmonized clinical laboratory testing.

First certified reference material for cystatin C in human serum ERM-DA471/IFCC

The IFCC Working Group for the Standardisation of Cystatin C (WG-SCC), in collaboration with the Institute for Reference Materials and Measurements (IRMM), announces the availability of the new certified reference material ERM-DA471/IFCC. The material was characterised using a pure protein primary reference preparation (PRP) as calibrant. The PRP was prepared from recombinant cystatin C, and its concentration measured using dry mass determination. The characterisation of ERM-DA471/IFCC was performed by particle enhanced immuno-nephelometry, particle enhanced immuno-turbidimetry, and enzyme amplified single radial immuno-diffusion. The certified cystatin C mass concentration in ERM-DA471/IFCC, if reconstituted according to the specified procedure, is 5.48 mg/L, the expanded uncertainty (k=2) being 0.15 mg/L.

Protein standardization III: Method optimization basic principles for quantitative determination of human serum proteins on automated instruments based on turbidimetry or nephelometry

Quantitative protein determinations in routine laboratories are today most often carried out using automated instruments. However, slight variations in the assay principle, in the programming of the instrument or in the reagents may lead to different results. This has led to the prerequisite of method optimization and standardization. The basic principles of turbidimetry and nephelometry are discussed. The different reading principles are illustrated and investigated. Various problems are identified and a suggestion is made for an integrated, fast and convenient test system for the determination of a number of different proteins on the same instrument. An optimized test system for turbidimetry and nephelometry should comprise high-quality antibodies, calibrators, controls, and buffers and a protocol with detailed parameter settings in order to program the instrument correctly. A good user program takes full advantage of the optimal reading principles for the different instruments. This implies--for all suitable instruments--sample preincubation followed by real sample blanking, which automatically corrects for initial turbidity in the sample. Likewise it is recommended to measure the reagent blank, which represents any turbidity caused by the antibody itself. By correcting all signals with these two blank values the best possible signal is obtained for the specific analyte. An optimized test system should preferably offer a wide measuring range combined with a wide security range, which for the user means few re-runs and maximum security against antigen excess. A non-linear calibration curve based on six standards is obtained using a suitable mathematical fitting model, which normally is part of the instrument software.

Protein standardization I: Protein purification procedure for the purification of human prealbumin, orosomucoid and transferrin as primary protein preparations

A procedure for the purification of human prealbumin, orosomucoid and transferrin as primary protein preparations has been developed. The procedure describes in detail the chemicals, the fractionation equipment and the purification of the three proteins from the same starting material (a 90-donor plasma pool). The fractionation steps involve methods like salting out, various anion and cation exchange chromatographies, preparative electrophoresis, and finally, size chromatography. Only mild and highly reproducible fractionation methods are used in order to obtain high recoveries. All of these provide the best guarantee that no serious subfractionation has taken place. At the same time, high recoveries are a necessity for the pure protein to be representative of the same protein in vivo. The following recoveries were obtained: prealbumin 55%, orosomucoid 70% and transferrin 85%. The pure proteins are produced as liquid calibrators (primary protein preparations) dissolved in one electrolyte (0.1 mol/l KCl) and stored in sealed glass ampoules at -80 degrees C. These three pure proteins were used as primary reference preparations in the certification of the international reference preparation CRM 470.