CONTEXT Proficiency testing (PT) participants can interpret their results to detect errors even when their performance is acceptable according to the limits set by the PT provider. OBJECTIVE To determine which rules for interpreting PT data provide optimal performance for PT with 5 samples per event. DESIGN We used Monte Carlo computer simulation techniques to study the performance of several rules, relating their error detection capabilities to (1) the analytic quality of the method, (2) the probability of failing PT, and (3) the ratio of the peer group SD to the mean intralaboratory SD. Analytic quality is indicated by the ratio of the PT allowable error to the intralaboratory SD. Failure of PT was defined (Clinical Laboratory Improvement Amendments of 1988) as an event when 2 or more results out of 5 exceeded acceptable limits. We investigated rules with limits based on the SD index, the mean SD index, and percentages of allowable error. RESULTS No single rule performs optimally across the range of method quality. CONCLUSIONS We recommend further investigation when PT data cause rejection by any of the following 3 rules: any result exceeds 75% of allowable error, the difference between any 2 results exceeds 4 times the peer group SD, or the mean SD index of all 5 results exceeds 1.5. As method quality increases from marginal to high, false rejections range from 16% to nearly zero, and the probability of detecting a shift equal to 2 times the intralaboratory SD ranges from 94% to 69%.

where 1 mm Hg equals 133 Pa, B.P. is barometricpressure,W.V.P.T iswater vapor pressure at the temperature of equilibration, and ar and a are the absorption coefficients of the gas at the temperature under consideration and at 37 #{176}C. From this relationship, a measured P02 of 187 mm Hg has been predicted (1) for an aqueous solution equilibrated at 24 #{176}C with a gas mixture composed of 21% oxygen, 12% carbon dioxide, and 67% nitrogen. Oxygen, however, does not act independently in this system, and the partial pressures of nitrogen and carbon dioxide at the measurement temperature of 37 #{176}C must be considered. Equation 1 predicts a p N2 and p co2 of 588 and 123mm Hg, respectively. If one includes a water-vapor pressure of 47 mm Hg, the total pressure calculated according to Dalton’s law is 945 mm Hg. Since this exceeds the barometric pressure, the solution must “boil off” gas until the sum of the vapor pressures is again equal to the atmospheric pressure. The difficulty with equation 1 is that it is based on the assumption (2) that the oxygen content of air saturatedwater isunchanged by increasing the temperature. A second phase of gas bubbles will form to accommodate the decreasing gas solubilities as the temperature increases. This phenomenon can be observed by letting a glass of cold water come to ambient temperature on a warm day. Because the gas bubbles formed are in intimate contact with the liquid phase, the partial pressures of the gases in the gas and liquid phases must be equal.Ifthey are not,mass transfer will occur to eliminate any concentration gradients. Consider the equilibration of water with a mixture of gases at temperature T, where T < 37 #{176}C. Let us isolate a 1-ml aliquot of this liquid, and consider its behavior after warming to and equilibration at 37 #{176}C. Let o be the volume of the individual gas in the gas phase, v be the volume of the individual gas in the liquid phase, and V be the total volume of the gas phase. The volume of each gas present in the liquid phase at T is equal to the sum of the volume of that gas present in the liquid phase and the gas phase at 37

The Clinical Laboratory Improvement Amendments of 1988 (CLIA 88) (1) have caused great changes not only in US laboratories but in clinical laboratories throughout the world. CLIA’s requirements for pre- and postanalytical control were harbingers of more complete approaches to the implementation of quality systems in clinical laboratories, such as the quality model just introduced by the National Committee for Clinical Laboratory Standards (2). CLIA’s maximum allowable error specifications for proficiency testing (the so-called CLIA limits) are being used by manufacturers to help set analytical performance goals for new laboratory analyzers. These specifications have ignited a transatlantic debate (3) regarding the formulation of analytical goals based strictly on patient variation vs the CLIA goals, which were based on a host of variables, including physician surveys, patient variation, analytical performance, and even prior proficiency testing (PT) performance. The enactment of CLIA 88 unraveled the comfortable existence of a few large PT providers who primarily served hospital laboratories. In the early 1990s, thousands of previously unregulated physician office laboratories were added to the PT pool. Many of these laboratories eventually subscribed to newly established PT providers whose missions were more closely aligned to the participants’ medical organizations, e.g., the American Academy of Family Physicians and the American Society of Internal Medicine. As of 1998, there were 20 different CLIA-certified PT programs (4). The presumably decreased profitability of the PT business has led to a commoditization of PT products and less effort expended in the design and manufacture of PT specimens for analytes that are not directly regulated by CLIA. Another result, coincident with the enactment of CLIA 88, was the development of PT programs that serve a narrow spectrum of users, such as those using instruments of a specific manufacturer. Finally, the requirement to subscribe to CLIA-approved PT programs has eroded the …

An assay for hepatitis B surface antigen (HBsAg) should reliably detect 0.2 microgram/L, the lowest reported concentration in an asymptomatic blood donor. The difference between this concentration and the assay cutoff defines the analytical quality requirement in a total error format. The design of a statistical QC procedure is critically dependent on the precision of the assay. The precision of a developmental ELISA of HBsAg under study ranged from 17.5% to 9.6% for controls containing 0.07 to 1.50 micrograms/L, respectively. Use of one positive control with the 1(3s), QC rule provided an 85% chance of detecting a critical loss of assay sensitivity; use of two positive controls increased the chance of detecting critical loss of assay sensitivity to nearly 100%. These rules are based on the precision of this developmental assay, and must be developed individually for other assays. The development of the proposed QC procedures illustrates how quantitative QC can be provided for qualitative assays.

The Clinical Laboratory Improvement Amendments of 1988 (CLIA 88) have made proficiency testing (PT) the most frequent external indicator of acceptable test performance. External agencies have very clear criteria for acceptable performance on PT; however, their guidelines are relatively weak tests of performance, and are not optimal for purposes of a laboratory's self-improvement. We used computer simulations to devise a multirule algorithm with high sensitivity to proficiency testing errors. The multi-rule consists of the 2/5(1SDI) screening rule, either the x(1SDI) or the x(1.5SDI) rules to identify systematic error and the 1(3SDI) and R(4SDI) rules to identify random error. We have applied this multirule to 16 months of proficiency test data from two different institutions and found that potential problems can be detected and corrected before PT failures occur. This procedure is also sensitive to small systematic errors that occur due to inherent between-run variations in assays; thus it is not proposed for use by external agencies for judging the acceptability of a laboratory's PT performance.

Although CLIA 88 has probably caused the laboratorian to place inordinate emphasis on proficiency testing, we believe that it will ultimately improve clinical laboratory practice. Due to the increased numbers of challenges within a mailing, the laboratorian has a greater ability to gauge magnitudes and types of any existing error. These magnitudes can be compared with previously established limits to determine the need for corrective action. Laboratories are encouraged to devise a system to guarantee accurate preanalytic, analytic, and postanalytic PT processing and reporting. Due to the relatively low imprecisions of today's hematology analyzers compared with the HCFA limits, most hematology laboratories should focus their attention on measures of and factors affecting long-term control and calibration. More attention should be paid to moving averages of indices and the analytic performance in regional or manufacturer control pools.

Journal Article Considerations for the Implementation of Clinically Derived Quality Control Procedures Get access George S. Cembrowski, MD, PhD, George S. Cembrowski, MD, PhD Park Nicollet Medical Center, and Department of Pathology and Laboratory Medicine, University of Minnesota, Minneapolis (Dr Cembrowski); Peninsula General Hospital and Department of Medical Technology, Salisbury State University, Salisbury, MD 21801 (Dr Carey). Search for other works by this author on: Oxford Academic PubMed Google Scholar R. Neill Carey, PhD R. Neill Carey, PhD Park Nicollet Medical Center, and Department of Pathology and Laboratory Medicine, University of Minnesota, Minneapolis (Dr Cembrowski); Peninsula General Hospital and Department of Medical Technology, Salisbury State University, Salisbury, MD 21801 (Dr Carey). Search for other works by this author on: Oxford Academic PubMed Google Scholar Laboratory Medicine, Volume 20, Issue 6, 1 June 1989, Pages 400–405, https://doi.org/10.1093/labmed/20.6.400 Published: 01 June 1989

Journal Article Quality Control in the 1990s Get access George S. Cembrowski, MD, PhD, George S. Cembrowski, MD, PhD Nicollet Medical Center and the Department of Pathology and Laboratory Medicine, University of Minnesota, Minneapolis (Dr Cembrowski); Peninsula General Hospital and the Department of Medical Technology, Salisbury State University, Salisbury, MD 21801 (Dr Carey). Search for other works by this author on: Oxford Academic PubMed Google Scholar R. Neill Carey, PhD R. Neill Carey, PhD Nicollet Medical Center and the Department of Pathology and Laboratory Medicine, University of Minnesota, Minneapolis (Dr Cembrowski); Peninsula General Hospital and the Department of Medical Technology, Salisbury State University, Salisbury, MD 21801 (Dr Carey). Search for other works by this author on: Oxford Academic PubMed Google Scholar Laboratory Medicine, Volume 20, Issue 6, 1 June 1989, Pages 375–376, https://doi.org/10.1093/labmed/20.6.375 Published: 01 June 1989

The authors examined both hard and soft glass evacuated blood-drawing tubes for possible effects on clinical chemistry measurements. Using routine laboratory procedures, no clinically or statistically significant difference could be detected in 34 analytes using 66 different methods. A special high-precision study utilizing an adaption of the NBS round-robin procedures for calcium, magnesium, sodium, and potassium detected no difference between paired sera when drawn or stored for 72 hours, or both, in the two types of glass. The authors conclude that the type of glass used in production of the evacuated blood-drawing tubes does not affect the clinical chemistry results obtained.