Erroneous Test Results Research Articles

Factorial Experiments When Factor Levels are Not Necessarily Reset

In industry, the run order of experiments is often randomized, but this does not guarantee that all factor levels are reset from one run to the next. When this happens and the levels of factors are the same in successive runs, the assumption of independent observations from run to run may be violated or incorrect. In this case, an ordinary least squares analysis can produce biased estimates of the coefficients in the model, which leads to erroneous test results and inferences.In this paper we describe how not resetting the levels of one or more factors in successive runs can result in less precision in parameter estimates and a larger than expected prediction variance. We present formulas for the prediction variance and the expected prediction variance for this situation. These quantities are important because they allow us to compare the prediction properties of experiments that are completely randomized to experiments where the levels of one or more factors are not reset. We give an analysis of an industrial experiment of this type and recommendations for carrying out factorial experiments where the levels of one or more factors are not reset.

Interpretation of atypical patterns encountered when using a flow cytometry-based method to detect residual leukocytes in leukoreduced red blood cell components.

Universal leukoreduction of blood components is becoming the standard of care. Flow cytometry methods are being used for quality control of the leukoreduction process. We provide an atlas of atypical flow cytograms generated by a commercial LeucoCOUNT assay that was used to enumerate residual leukocytes in leukoreduced red blood cell components. Numeric results are derived from a flow cytogram generated by the assay. Three types of atypical flow cytogram patterns were observed during process validation or routine quality control of leukoreduced red blood cell components. (a) Fixation artifact: Fixation of control or test samples can alter the staining intensity compared with fresh cells. (b) "Rain" pattern: Flow cytometry methods count slightly damaged leukocytes not removed during leukoreduction. Slightly damaged leukocytes appear on a flow cytogram like "rain" falling from a well-defined "cloud" of intact residual leukocytes. Discrepancies between automated flow cytometry results and subjective manual counting methods can occur. (c) Autofluorescence-debris pattern: Cell debris and age-related changes in the sample can cause shifts in the fluorescence staining pattern, resulting in erroneous test results. Review of flow cytograms is essential for accurate reporting of flow cytometry-based methods for enumerating residual leukocytes in leukoreduced blood components.

Evaluation of LabRespond, a New Automated Validation System for Clinical Laboratory Test Results

Manual validation of laboratory test results is time-consuming, creating a demand for expert systems to automate this process. We have started to set up the program "LabRespond", which covers five validation levels: administrative, technical, sample, patient, and clinical validation. We present the evaluation of a prototype of an automated patient validation system based on statistical methods, in contrast to the commercially available program "VALAB", a rule-based automated validation system. In the present study, 163 willfully altered, erroneous test results out of 5421 were submitted for validation to LabRespond, VALAB, and to a group of clinical chemists (n = 9) who validated these test results manually. The test results rejected by three or more clinical chemists (n = 281) served as a secondary reference standard. The error recovery rates of clinical chemists ranged from 23.9% to 71.2%. The recovery rates of LabRespond and VALAB were 77.9% and 71.8%, respectively (difference not significant). The false-positive rates were 82.7% for LabRespond, 83.6% for VALAB, and 27.8-86.7% for clinical chemists. Using the consensus of three or more clinical chemists as the secondary reference standard, we found error recovery rates of 64.8% for LabRespond and 72.2% for VALAB (P = 0.06). Compared with VALAB, LabRespond detected more (P = 0.003) erroneous test results of the type that were changed from abnormal to normal. The statistical plausibility check used by LabRespond offers a promising automated validation method with a higher error recovery rate than the clinical chemists participating in this study, and a performance comparable to VALAB.

Influence of single-phase excitation and magnetizing reactance on transformer leakage reactance measurement

Low voltage and single-phase excitation are often used to measure leakage reactance or short-circuit impedance of transformers. Winding distortion may be detected by comparing field results with factory nameplate values measured at 25-100% of the rated current using three-phase excitation. The results of single- and three-phase excitation will not always correlate. If the voltage applied in the field is not properly selected then the data may be influenced by the magnetizing reactance. The resulting difference between the nameplate value and the field data might then lead to erroneous analysis of test results and could be interpreted as an indication of winding distortion. The intent of this paper is to analyze the physics of the process and gain insight on test circuit selection and analysis of the results. Methods for avoiding erroneous test results are suggested.

Chlamydial infection

The need for a cost-effective, highly sensitive and specific test for Chlamydia trachomatis infection remains, although progress is being made. Clinicians can minimize the incidence of complications and erroneous test results by being alert to the possibility of this infection, screening appropriate patients, using careful collection techniques, following the most recent treatment recommendations, and knowing the limitations of available tests.

High-Dose Hook Effect in a Two-Site IRMA for Measuring Thyrotropin

The 'high-dose hook effect' in sandwich immunoassays has been recognized and studied for more than a decade.? Assays in which both antibodies to the analyte are added at the same time (rather than sequentially), and thus have no 'wash' step or equivalent in between to remove unbound analyte, are particularly susceptible. When the hook occurs at concentrations far beyond those usually encountered in clinical practice, there is little risk of erroneous test results. However, for some tests, such as those determining tumour marker concentrations where homeostatic mechanisms are not involved, the range encountered can be broad enough. to include the region of the hook. Extremely high hormone concentrations also occur and may fall in the range of the hook effect, although this would be quite unusual in the case of thyrotropin (TSH). A description of the hook effect in a two-site monoclonal immunometric assay for TSH has not been published. We have recently encountered a patient with thyroid hormone resistance associated with very high serum TSH concentrations. Following stimulation with thyrotropin releasing hormone (TRH), TSH concentration reached a peak of 1600mIU/L. Initial results, when neat serum was used, fell between 50 and 100mIU/L as determined by extrapolation (by our data reduction program). Considerable dilution was necessary to bring the response on to the standard curve (0-50) and revealed the much higher concentrations. We had, then, the assay response in a number of neat samples with very high TSH concentrations. We also knew the actual TSH concentrations in these specimens, based on dilutions assayed subsequently. Putting these data together we had an opportunity to examine the

Evaluation of the Titertek-Enterobac-Automated System (TTE-AS) for Identification of Members of the Family Enterobacteriaceae

The Titertek-Enterobac-Automated System (TTE-AS, Flow Laboratories, Meckenheim, FRG) was evaluated for identification of members of the family of Enterobacteriaceae using a total of 816 bacterial strains obtained from stock cultures and clinical specimens. A comparison of the results of the TTE-AS kit with conventional methods was conducted. Identifications were classified as correct, not identified (two or more taxa possible, identification score < 80%, supplementary tests for final identification were not performed), and incorrect. Correct identification results were further subdivided according to the level of identification by species or biotype: (a) ≥ 98%, (b) 90% to 97%, (c) 80% to 89%. When compared with conventional identification results, the TTE-AS system correctly identified 95.3% (778 of 816 strains), 90.0% (734 strains) belonging to category (a), 3.4% (28 strains) belonging to category (b), and 2.0% (16 strains) belonging to category (c). For 18 (2.2%) of the remaining strains, the system generated the correct identification result, but with an identification level < 80% (low discrimination results). 11 strains (1.3%) were misidentified and the system failed to generate identification results with 9 strains (1.1%). Reactions within TTE-AS were reproducible with an estimated probability of erroneous test results of 1.7%.

Mechanical properties of injection moulded iron-nickel alloys

Extensive work was performed to determine a suitable geometry that would provide test specimens which would yield meaningful and reproducible results. Important injection moulding processing variables which cause defects that spawn erroneous test results were thoroughly investigated. Several properties were analysed: tensile strength, yield strength, elongation, notch impact strength. Electron and optical microscopy was used to determine structure property relationships as well as failure analysis and establishing fracture modes.

Evaluation of the Titertek-NF system for identification of gram-negative nonfermentative and oxidase-positive fermentative bacteria.

The Titertek-NF (TT-NF) system (Flow Laboratories GmbH, Meckenheim, Federal Republic of Germany) was evaluated for the identification of 1,289 strains of gram-negative, nonfermentative bacteria and some gram-negative, oxidase-positive bacteria. The oxidase test was also performed. Identifications were classified as correct, not identified (two or more taxa possible and identification score of less than 80%; supplementary tests for furthering the identification were not performed), and incorrect. Correct identification results were further subdivided by the correct level of species or biotype identification as greater than or equal to 98% (category a), 90 to 97% (category b), and 80 to 89% (category c). When compared with conventional identification results, the TT-NF system correctly identified 90.3% of strains (1,164 of 1,289 strains), with 72.5% (935 strains) belonging to category a, 14.7% of strains (189 strains) belonging to category b, and 3.1% of strains (40 strains) belonging to category c. Among the remaining strains, 104 (8.1%) were not identified and 14 (1.1%) were misidentified, and the system failed to generate identification results for 7 strains (0.5%). Reactions within the TT-NF system were reproducible, with an estimated probability of erroneous test results of 0.2%.

Erroneous test results obtained with the Tandem-E TSH kit.

Journal Article Erroneous test results obtained with the Tandem-E TSH kit. Get access M C Smith, M C Smith Search for other works by this author on: Oxford Academic Google Scholar M E Brown, M E Brown Search for other works by this author on: Oxford Academic Google Scholar J H Morel, J H Morel Search for other works by this author on: Oxford Academic Google Scholar S C Woodward S C Woodward Search for other works by this author on: Oxford Academic Google Scholar Clinical Chemistry, Volume 34, Issue 9, 1 September 1988, Pages 1946–1947, https://doi.org/10.1093/clinchem/34.9.1946 Published: 01 September 1988

Erroneous test results after use of pieced-together rotors in a Cobas Fara centrifugal analyzer confirmed.

Erroneous test results after use of pieced-together rotors in a Cobas Fara centrifugal analyzer confirmed.