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Data from 2.5 million glucose analyses on pools of lyophilized human quality control serum were used to evaluate analyte stability in the prereconstitution phase. Input information was from laboratories in Regional Quality Control Programs that use CAP Quality Assurance Service (QAS) data processing. Of 31 pools in use between 1977 and 1981, decreasing glucose concentration was detected by, at least, one method in 26 pools, and by two or more methods in 21 pools. Method-associated average decrease in concentration varied from 0.13 mg/dL/month (glucose oxidase-electrode) to 0.19 mg/dL/month (automated glucose oxidase-colorimetric). Bidirectional instability as a function of analytic method, i.e., increase with "mild" methods, decrease with "rigorous" methods that was noticed previously with pools analyzed between 1973 and 1977, was no longer seen. Dominant directional changes in the later pools were downward by all methods, when statistically significant trends were demonstrated.

Over a 12-month period, between July 1981 and June 1982, 115 active participants in the Microbiology program of the College of American Pathologists Quality Assurance Service (QAS) submitted a total of 555,619 individual determinations on three quality control reference strains using the NCCLS standardized disc diffusion procedure. Data is presented for those antimicrobic agent/reference strain combinations for which NCCLS control limits have been changed since the last report of QAS microbiology data or that continue to show discrepancies with current NCCLS individual daily test control guidelines. Data for Escherichia coli versus cefoxitin, doxycycline, and nalidixic acid and for Staphylococcus aureus versus cefoxitin, nafcillin, and oxacillin show good compliance with the new NCCLS guidelines and distributions that are all approximately Gaussian. Significant discrepancies were noted for six combinations; cefamandole, cephalothin, neomycin, and nitrofurantoin versus E. coli and amikacin and clindamycin versus S. aureus. Of these discrepancies, only neomycin/E. coli and amikacin/S. aureus can be accounted for by a subpopulation of laboratories, which, when removed, corrects the data.

The evaluation of quality control (QC) practices from the College of American Pathologists (CAP) Microbiology Surveys demonstrates a trend away from daily controls similar to that first noted in 1980. Previous recommendations for more relevant cost-containment oriented weekly QC procedures are discussed, and the 1982 CAP Surveys statistics confirm earlier comparability between the daily and weekly QC participant groups. Each QC practice subgroup (daily or weekly) had nearly identical mean disk inhibitory zone diameters, and the performance accuracy on two 1982 challenge strains were very similar. Generally, disk zone diameter from those laboratories using weekly QC were smaller, but the frequency of minor and major (false-resistant) errors was only slightly increased. The authors recommend the conversion to weekly QC of disk or dilution antimicrobial susceptibility tests after an acceptable daily QC performance has been established (See criteria in discussion).

The College of American Pathologists' Enzyme Survey continues to provide a valuable measure of the analytic quality of clinical enzymology for its participants and for the laboratory community. An updated reporting format for the participants simplifies the interpretation of Enzyme Survey data and should make it more valuable for detecting short- and long-term changes in accuracy and precision. A short-term CV of 3% and a long-term CV of 6% are recommended as analytic goals for the five enzymes described here. The upper limit of normal used by many laboratories is appropriate for a given enzyme yet remains as an area requiring urgent further study.

We establish that, for the analytes aspartate aminotransferase, glucose, phosphorus, and potassium, there is significant correlation between laboratory performance as determined by College of American Pathologists-sponsored external (Surveys) and expanded internal (regional) quality control (Quality Assurance Service) programs. However, relatively low parametric and nonparametric correlation coefficients and significant departure of linear regression slopes from unity reflect major differences in the calculated parameters of absolute bias, precision, and total error obtained through internal and external quality control. Significantly better performance in both Surveys and the Quality Assurance Service was documented for laboratories participating in the College of American Pathologists Laboratory Accreditation Program. Multiple descriptors of laboratory quality, as indicated here, are superior in describing laboratory performance to proficiency testing alone. As a bridge between external and internal quality control, shared pools of quality control materials are described for use as unknown Survey challenges and subsequent distribution for regional quality control. Such programs, which can be configured to serve thousands of laboratories, could offer cost savings, better quality assurance, and improved characterization of laboratory performance by minimizing interprogram differences in control matrix and method classification and providing greater reliability of target values.

Data from magnesium and iron analyses of pools of lyophilized quality control serum were used to evaluate stability of analyte mean values in the pre-reconstitution period. Information was received from laboratories in Regional Quality Control Programs between 1977 and 1981, using CAP Quality Assurance Service data processing. For magnesium, 28 of 41 (68%) pool-method combinations were stable, 11 (27%) showed decreases, and 2 (5%) showed increases. Decreases averaged 0.008 mg/dL/month (all methods). A pronounced effect of method (automated methylthymol blue) and year correlated with decreases in measurable magnesium. For iron, 45 of 56 (80%) pool-method combinations were stable, 8 (15%) showed decreases, and 3 (5%) showed increases. Decreases averaged 0.349 g/dL (all methods). In most cases, changes in measured concentrations are attributed to methodologic factors, rather than intrinsic changes in analyte concentrations.