An algorithm for finding the linear region in a nonlinear data set.

Finding the linear reportable range is an important procedure for each method in clinical chemistry. One is often called upon to limit the reportable range in order to find the linear region. Limiting the reportable range by visual techniques is subjective, may introduce bias and is not programmable. Using Kroll and Emancipator's polynomial method for linearity, we compare the residuals of a test to determine whether eliminating a point from one end or the other of the data set worsens or improves the data sets' linearity. In an example of urinary cortisol, the root mean squares of the residuals improve by 2% when the lowest point is removed, 39% when the highest point is removed and 82% when the two highest points are removed. The latter data set is the most linear.

The usefulness of calibration verification and linearity surveys in predicting acceptable performance in graded proficiency tests.

OBJECTIVE: To assess the association between performance on graded chemistry surveys and evaluation of linearity and calibration in Linearity surveys. DESIGN: Data from Linearity Surveys (LN series) and from routine comprehensive College of American Pathologists chemistry surveys (all series) were used to evaluate the hypothesis that laboratories with nonlinear or univerified calibration would have a greater likelihood of unacceptable performance on comprehensive chemistry surveys. RESULTS: This study found that acceptable calibration verification evaluation is significantly related to acceptable rates for most analytes, including albumin, calcium, chloride, glucose, iron, magnesium, sodium, total bilirubin, uric acid, high-density lipoprotein cholesterol, triglycerides, alkaline phosphatase, alanine and aspartate aminotransferase, digoxin, gentamicin, phenobarbital, procainamide, and thyroxine. CONCLUSION: There is a consistent and strong relationship between calibration verification problems in the Linearity Surveys and failure rates in the College of American Pathologists chemistry surveys. Laboratories with poor calibration evaluations on Linearity Surveys have higher unacceptable rates on proficiency tests. Individual laboratories who were rated linear and whose calibration was verified by Linearity Surveys have lower unacceptable rates.

College of American pathologists experience with the linearity surveys, 1987-1991.

The Instrumentation Resource Committee has offered a survey since 1988 to perform and evaluate linearity. The survey uses a serum-based material and satisfies federal regulations that require linearity evaluations in the clinical laboratory. Both statistical and empirical methods to determine linearity were developed for the survey. Participant results have shown a high rate of nonlinear methods that may be due to our inability to accurately determine linearity or may reflect the true state of clinical assays. The survey shortcomings and future projects are discussed.

Laboratory evaluation of the Boehringer Mannheim "Hitachi 705" automatic analyzer.

We evaluated a new multi-channel chemistry analyzer, the Hitachi 705 Automatic Analyzer, marketed by Boehringer Mannheim Diagnostics, Inc. The instrument is a computer-controlled discrete analyzer, which can be run in a combination profile mode and single-test mode. Sixteen different tests per sample may be performed at the rate of 180 tests per hour. The Hitachi 705 is especially suitable for use in hospitals that do not perform profile testing. Precision and linearity were excellent and the instrument was relatively trouble-free, with little operator attention required during operation. The Hitachi 705 was easily interfaced to our laboratory computer. We compared the performance of the instrument with that of the Du Pont aca; the two instruments compared favorably.

Focusing on the laboratory, not the computer.

Much time and effort is spent comparing laboratory computer systems; the process is not unlike that of shopping for an automated chemistry analyzer. But the authors believe too little effort is expended in examining and understanding the laboratory functions that are to be computerized and, as a consequence, computer purchases fail to reach expectations. Here, they emphasize the importance of evaluating laboratory functions, particularly the area of communication and record keeping.