A penile ulceration in a patient with the acquired immunodeficiency syndrome. Foscarnet-induced penile ulceration.
Explore the source record for details and available documents.
Acquired Immunodeficiency Syndrome↗
Biomedical subjects
W G Miller
Publications and source records attributed to W G Miller.
Partial likelihood analysis of within-unit variances in repeated measurement experiments.
The objectives of some experiments are to compare the variances of two or more treatments, products, or techniques. If the investigator is more concerned about within-unit variances rather than between-unit variances, then a repeated measurement design is needed. We invoke a random effects model with heterogeneous within-unit variances for certain repeated measurement designs. We do not impose any distributional assumptions for the random effects, whereas we assume either a normal or multivariate t distribution for the random errors. We propose a partial likelihood analysis for population-based inference and individual-based inference. We illustrate the methodology with an example from a trial comparing serum cholesterol measurements from a routine laboratory analyzer to those of a standardized method.
Analysis of Variance↗
Measurement of free phenytoin in blood with a self-contained fiber-optic immunosensor.
We describe the measurement of the anticonvulsant drug phenytoin (5,5-diphenylhydantoin) in human blood and plasma using a self-contained fiber-optic immunosensor which gave a reversible response to changes in concentration. No regenerative treatment of the immunosensor was required between measurements. The analytical signal depended on the degree of energy transfer from B-phycoerythrin labeled with phenytoin to Texas Red labeled anti-phenytoin antibody. Dextran 70K was added to the reagent system to equalize the oncotic pressure across the encapsulation membrane. A gas chromatography reference method was used to measure free drug concentrations. Regression analysis for plasma samples gave the relationship (sensor) = 1.02 (reference) + 0.07 microM; Syx = 1.00 microM; r = 0.953; sensor mean 4.45 microM; reference mean 4.31 microM. Sensor performance in plasma and whole blood was essentially equivalent. We demonstrate the feasibility of measuring free phenytoin directly in blood and suggest that the sensor design is generally applicable for the measurement of other haptens in blood.
Biosensing Techniques↗
Characteristics of a Brucella species from a bottlenose dolphin (Tursiops truncatus).
A culture isolated from an aborted fetus of a bottlenose dolphin (Tursiops truncatus) was characterized. The isolate was a gram-negative coccobacillus, and the colonial morphology was typical of a smooth Brucella. The isolate was positive for catalase, oxidase, nitrate reduction, and urease. Hydrogen sulfide was not produced. It grew in air at 37 C but required 72 hours for good growth. There was growth on media containing basic fuchsin, thionin, thionin blue, penicillin, and erythritol. The M antigen was dominant, and the isolate was lysed by 4 of 10 brucellaphages tested. The oxidative metabolic profile of the isolate was similar to that for B. abortus but differed in utilization of L-asparagine, L-glutamic acid, and DL-citrulline. Whole-cell lysates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein profiles were markedly different from the protein profiles of reference strains of Brucella species. Biochemical and oxidative metabolism profiles indicated that the isolate belongs in the genus Brucella but did not match the profiles of any established species or biovars. This isolate may be an atypical strain of a recognized Brucella species or a new biovar or species of Brucella.
Animals↗
Evaluating test methods by estimating total error.
A common procedure for evaluating a test method by comparison with another, well-accepted method has been to use a repeated measurements design, in which several individual subjects' specimens are assayed with both methods. We propose the use of the intrasubject relative mean square error, which is a function of the intrasubject relative bias and the coefficient of variation of the test method, as a measure of total error. We construct for each individual subject a score that is based on how well an individual's estimate of total error compares with a maximum allowable value. If the individual's score is > 100%, then that individual's estimate of total error exceeds the maximum allowable value. We present a distribution-free statistical methodology for evaluating the sample of scores. This involves the construction of an upper tolerance limit to determine whether the test method yields values of the total error that are acceptable for most of the population with some level of confidence. Our definition of total error is very different from that defined in the National Cholesterol Education Program (NCEP) guidelines. The NCEP bound for total error has three main problems: (a) it incorrectly assumes that the standard error of the estimated relative bias is the test coefficient of variation; (b) it incorrectly assumes that the individual estimated relative biases follow gaussian distributions; (c) it is based on requiring the relative bias of the average individual in the population to lie within prescribed limits, whereas we believe it is more important to require the total error for most of the individuals in the population, say 95%, to lie within prescribed limits.
Bias↗
Chromosomal supercoiling in Escherichia coli.
The Escherichia coli chromosome is compacted into 40-50 negatively supercoiled domains. It has been proposed that these domains differ in superhelical density. Here, we present evidence that this is probably not the case. A modified Tn10 transposable element was inserted at a number of locations around the E. coli chromosome. This element, mTn10-plac-lacZ+, contains the lac operon promoter, plac, whose activity increases with increasing superhelical density, fused to a lacZ+ reporter gene. Although mTn10-plac-lacZ+ fusion expression varies as much as approximately threefold at different insertion sites, the relative levels of expression from these elements are unaffected by replacing plac with the gyrA promoter, pgyrA, which has a reciprocal response to changes in superhelical density. Importantly, topoisomerase mutations and coumermycin, which inhibits DNA gyrase activity, alter mTn10-plac-lacZ+ and mTn10-pgyrA-lacZ+ fusion expression in expected ways, showing that the elements remain responsive to supercoiling and that topoisomerase activity is required for maintaining superhelical density. Fusion expression is not affected by anaerobic growth or osmotic shock, two physiological conditions thought to alter supercoiling. The approximately threefold difference in mTn10-plac-lacZ+ and mTn10-pgyrA-lacZ+ fusion expression observed at different sites may be explained by regional differences in chromosomal copy number that arise from bidirectional replication. Together, these results strongly suggest that the E. coli chromosomal domains do not differ in functional superhelical density.
Anaerobiosis↗
Assay instrument-dependent matrix effects in standardization of cholesterol measurements.
Human serum-based frozen reference materials have been used by the Centers for Disease Control and Prevention (CDC)-National Heart, Lung and Blood Institute Lipid Standardization Program to improve the precision and accuracy of blood cholesterol measurements. Occasionally, laboratories in the program have had problems obtaining results for patients' fresh serum samples equivalent to those obtained with frozen CDC standardization pools. This incompatibility of sample, reagent, instrument, and assay characteristics has been labeled broadly as a "matrix effect," which usually is attributed to unknown characteristics of the processed pool material. In this study we showed that a large negative bias obtained with CDC pools was attributable to use of the sample blank mode on the Cobas-Bio analyzer. However, under the same conditions, fresh patients' serum samples were analyzed accurately. The use of a blank absorbance immediately after mixing sample and reagents (the "autoblank" mode) allowed the instrument to accurately analyze both fresh serum samples and CDC standardization pools and thus allowed the documentation of traceability of the cholesterol measurements to the National Reference System for Cholesterol.
Bias↗
Total error assessment of five methods for cholesterol screening.
We report the accuracy, imprecision, total analytical errors, and patient misclassification errors for cholesterol measured from capillary whole blood, venous whole blood, and venous plasma samples by five devices used in public cholesterol screening environments: Reflotron, Vision, Ektachem DT-60, QuickRead, and Liposcan. None of the methods met the National Cholesterol Education Program (NCEP) performance recommendations of 3% CV with 3% bias. The Vision and Reflotron methods used with venous samples gave individual results with total errors consistent with a combined CV and bias in the 4-5% range; capillary blood samples had total errors > 5% (combined CV and bias criteria). The DT-60 performance was near the 5% total error criterion for capillary samples and was > 5% for venous samples. Misclassification of individuals into desirable or referral groups for venous samples was as great as 5.1% for the DT-60, 5.7% for the Vision, and 7.1% for the Reflotron. Misclassifications for capillary blood samples were as great as 6.7%, 18.3%, and 14.1% for DT-60, Vision, and Reflotron, respectively. The QuickRead and Liposcan results were substantially poorer than those obtained by the other methods.
Adult↗
College of American Pathologists Conference XXIII on matrix effects and accuracy assessment in clinical chemistry: introduction.
Explore the source record for details and available documents.
Bias↗
Effect of freezing on cholesterol in individual sera.
Explore the source record for details and available documents.
Adult↗
DNA from diverse sources manifests cryptic low-level transcription in Escherichia coli.
We present evidence that DNA from diverse prokaryotic and eukaryotic sources gives rise to low-level fusion expression in Escherichia coli promoter-probe vectors. This expression may be as high as approximately 10% of the E. coli lacUV5 promoter. Although expression does not correlate with the presence of obvious E. coli promoter-like sequences, it is blocked by transcriptional terminators. Furthermore, transcription across the fusion junction is detected at levels that correlate with fusion expression. We suggest that this 'low-level transcription' (LLT) results from infrequent initiation by RNA polymerase at random sites and/or weak promoters. We propose that LLT has biological significance. In some instances, it may provide an advantageous basal level of gene expression, and we suggest that this may be true for the E. coli lacY gene. In other instances, LLT may be detrimental, in which case it may be blocked by mechanisms such as RNA secondary structure or transcriptional polarity. We present evidence to show that activation of the IS10 transposase gene by LLT is blocked at the translational level.
Base Sequence↗
Determination of magnesium in serum by the technicon SMAC with a calmagite method with blank correction.
Explore the source record for details and available documents.
Azo Compounds↗
Regional interlaboratory standardization of determinations of cholesterol, high-density lipoprotein cholesterol, and triglycerides.
The Clinical Chemistry Forum of Central Virginia initiated a lipid standardization program to help ensure that its members meet the current National Cholesterol Education Program guidelines for cholesterol testing, and to standardize assays of high-density lipoprotein (HDL) cholesterol and triglycerides so as to provide accurate lipid profiles. We found that freshly collected, never-frozen human sera must be used to assess interlaboratory accuracy for cholesterol, HDL cholesterol, and triglycerides assays, and that at least 23 samples are required to detect a 3% bias with 90% power when the between-laboratory imprecision (CV) is 3%. After recalibration, all 12 laboratories had a mean HDL cholesterol bias less than or equal to 5%, nine of 10 laboratories had a mean HDL cholesterol bias less than or equal to 40 mg/L for samples with values less than or equal to 570 mg/L, and 10 of 12 laboratories had a mean triglycerides bias less than or equal to 10% for fresh human sera split between participants and the Centers for Disease Control. Pools of frozen human sera were shown to have matrix biases greater than 3% for cholesterol in seven of 11 laboratories, and greater than 40 mg/L for HDL cholesterol in six of nine laboratories.
Blood Specimen Collection↗
A background-free assay for cells forming antibody to glucose oxidase coupled with an enzyme-linked immunosorbent assay (ELISA) to quantitate antibody secretion.
We describe an immunocytochemical assay for cells forming antibody to glucose oxidase (GO). The method is specific in that only cells containing intracytoplasmic antibody capable of binding the immunogen (GO binding cells; GOBC) are stained. The method is sensitive because there is no GO activity in mammalian tissues. This lack of background readily permits detection of one GOBC among 10(6) nucleated lymphohemopoietic cells. The technique is reliable because purified chemicals are used. Although it is not possible to determine the Ig class of antibody formed by an individual cell, as can be done with the hemolytic plaque assay, the amount and class of secreted antibody to GO can be quantitated by an indirect enzyme-linked immunosorbent assay (ELISA), which is also described. GO is immunogenic and stimulates the formation of large numbers of GOBC in the popliteal lymph nodes after injection with adjuvant into the footpads of mice, but 1-mg doses injected IV or IP are lethal because of its enzymatic activity, which causes hypoglycemia and methemoglobinemia.
Animals↗
An automated procedure for measuring biotinidase activity in serum.
In this automated procedure for quantifying biotinidase activity in human serum, a manual colorimetric method that measures conversion of the enzyme's artificial substrate N-biotinyl p-aminobenzoate was modified for use with a Technicon AutoAnalyzer II. The intra-run replicate precision (CV) was 2.1% and the day-to-day CV was 4.6% for quality-control sera. Results were linearly related to biotinidase activity in serum over the complete range of clinically relevant values, 0.2 to 11.0 U/L. Moreover, results of the automated assay were not significantly different from those of the manual assay. Because the automated procedure is faster and more precise, we recommend it for population-based studies and some screening studies.
Amidohydrolases↗
Fiber optic immunochemical sensor for continuous, reversible measurement of phenytoin.
This fiber optic sensor, based on a homogeneous fluorescence energy-transfer immunoassay, operates in a continuous, reversible manner to quantify the anticonvulsant drug phenytoin. B-Phycoerythrin-phenytoin and Texas Red-labeled antibody to phenytoin were sealed inside a short length of cellulose dialysis tubing, which was cemented to the distal end of an optical fiber. When the sensor was alternately placed into solutions with various concentrations of free phenytoin, the drug crossed the dialysis membrane and displaced a fraction of the B-phycoerythrin-phenytoin from the antibody. The resulting change in fluorescence signal was measured with a fiber optic fluorometer. A typical competitive-binding calibration curve was seen between 5 and 500 mumol of phenytoin per liter. Equilibrium response time ranged from 5 to 30 min for different sensors. Replicate equilibrium measurements with one sensor, alternated eight times between two solutions of phenytoin, gave a CV of 2.1% (n = 16) at 0 mumol/L and 2.4% (n = 13) at 100 mumol/L. A reversible immunochemical sensor can be made that has a response time suitable for continuous concentration measurements.
Energy Transfer↗