Internal Quality Control Materials Research Articles

Quality Assurance and Reproducibility of High-Resolution Two-Dimensional Electrophoresis and Silver Staining in Polyacrylamide Gels

Qualitative data from high-resolution two-dimensional electrophoresis (2DE) have become clinically useful in immunoglobulin clonality analysis, in resolution of ambiguities in immunofixation typing of paraproteins, and in genetic typing of serum proteins. Since 1986, the authors have been evaluating the College of American Pathologists Reference Preparation for Serum Proteins (RPSP) as a quality control material for 2DE because (1) it is prepared exclusively from pooled human sera, (2) the pool yields a reference pattern of mixed heterozygosity for genetic markers, and (3) RPSP is widely available as a lyophilized preparation that currently serves in the authors' laboratory as a qualitative quality control preparation and that may become a quantitative quality control material or external quality assessment material for 2DE. Using the ISO-DALT 2DE system and silver-staining, the peptide patterns were examined in 11 lots of RPSP and compared with fresh serum and with each other. Consistent differences in the 2DE pattern between RPSP and fresh serum included the presence of freeze-thaw peptides, the presence of degradation spots of apolipoprotein A-I, and the diminution of apolipoprotein spot intensities in RPSP. All lots of RPSP yielded clear identification of the eight serum proteins used for quality control calculations. Run-to-run coefficients of variation for a single lot of RPSP for four parameters of 2DE spot location and gradient reproducibility were comparable with band location reproducibility for the one-dimensional procedures of serum protein electrophoresis and lactate dehydrogenase isoenzyme electrophoresis. It is concluded that the reproducibility, that is, imprecision, of 2DE is the same as one-dimensional clinical electrophoresis techniques and that either RPSP or pooled fresh serum can serve as a satisfactory internal quality control material.

The use of internal quality control materials for the preparation and maintenance of reliable methods for the measurement of lead in blood

The performance of a group of reference laboratories measuring lead in blood, has been monitored by an intensive external quality assessment programme, since 1974. Performance was similar to that observed in other, larger quality control surveys but rapidly improved following detailed investigations of critical factors in the analytical methodology. The introduction of a rigorous internal quality control protocol, with all laboratories using the same well-characterised materials, has produced external quality control results that are both accurate and very tightly distributed. Between-laboratory coefficients of variation of less than 5%, less than 6% and less than 20% are now obtained at concentrations of over 1.0 μmol/l (20.7 μg/dl), 0.5–1.0 μmol/l (10–20 μg/dl) and less than 0.5 umol/l (10 μg/dl), respectively. These results represent the best that can be achieved by current methodology and instrumentation in regular, daily use.

Reference materials for measurement of aluminium in biological samples

There has been a large increase in the number of laboratories measuring aluminium in biological samples during the last 5–10 years. Most use ETA-AAS but many have had little previous experience with the technique and have encountered considerable problems in obtaining reliable results. Data derived from external quality assessment programmes show that a small group of successful laboratories can be identified. A detailed examination of the procedures used by these laboratories suggests that good results are obtained when the sample preparation and calibration methods are relatively simple. Background correction is not necessary, neither is the use of L'vov platforms. The most important feature is the careful attention to detail provided by a skilled, experienced analyst, assisted by reliable internal quality control materials. Suitable reference materials for water and dialysis fluids are urgently needed.