Limitation of the Vitros dry-slide technique in measuring high concentrations of salicylate in plasma.
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Blood Chemical Analysis↗
Biomedical subjects
F D Lasky
Publications and source records attributed to F D Lasky.
Designing in quality through design control: a manufacturer's perspective.
Quality by design is a comprehensive program that begins with understanding user needs and continues through (but does not end with) monitoring customer acceptance. Management tools and processes such as ISO 9000 standards and the Food and Drug Administration Quality System Regulations exist to guide medical device manufacturers in quality practices. The goal is to deliver products acceptable for their intended use. Quality control begins with defining attributes ranging from color to accuracy and precision. Failure mode and effects analysis and risk analysis consider both probability and severity of potential malfunctions and their effects on patients or operators. Tools used to implement design and production practices include Program Evaluation and Review Technique (PERT) charts and industry-conceived concepts, such as Six Sigma techniques. Their use varies with manufacturer, depending on product and customer needs and the manufacturer's specific quality practices. Verification confirms that input goals are met. Then, validation assures that intended clinical needs are continually satisfied by establishing adequate production specifications. Conformance is monitored to verify that stable, consistent processes are in place, and precise user instructions enable the device to satisfy its intended use. Finally, complaint tracking can help assess whether needs have been met. Modifications in service, hardware, or instructions (including quality control) might be required. Therefore, both manufacturers and users work in partnership for continual improvement. The manufacturer's knowledge of design, production, and service needs of its devices enable it to recommend appropriate quality-control protocols for clinical testing.
Chemistry, Clinical↗
Achieving accuracy for routine clinical chemistry methods by using patient specimen correlations to assign calibrator values. A means of managing matrix effects.
Accurate results obtained from routine methods used in the clinical laboratory can be achieved if the methods are traceable to definitive or reference methods or are based on widely accepted methodologic principles. At Eastman Kodak Co (Rochester, NY), we assign calibrator values for each method that is available on Kodak Ektachem analyzers by correlation to a reference method or a methodologic principle using patient specimens. Kodak's Reference Laboratory is responsible for maintaining the accuracy and consistency of the reference method or methodologic principle by standardizing with National Institute of Standards and Technology materials, where available, monitoring performance through statistical process control, participating in proficiency testing programs, and following procedures consistent with the International Organization for Standardization guideline, "General Requirements for the Competence of Calibrations and Testing Laboratories (ISO 25). "Patient samples that span the reportable range are run in replicate on the reference method or methodologic principle over several days. These patient sample results are then used to create a calibration curve based on the relationship of concentration to the raw response of the routine method, where the same patient samples are also run in replicate on the same day. Each day, multiple vials of stable calibrator fluids are included in these tests, along with control materials. Each calibrator is assigned a value of equivalent concentration (in millimoles per liter) by predicting the concentration that would be present at the measured response if the test fluid were a patient sample. These are termed supplementary assigned values (SAVs). The same calibrators can be used to compensate for matrix effects resulting from changes in reagent formulations, by appropriately adjusting the assigned values. For example, when a process improvement for Kodak Ektachem clinical chemistry slides for phosphorus was introduced, an SAV change of 0.39 mmol/L (1.2 mg/dL) was required for one calibrator to maintain accuracy of the patient samples. A comparison of patient samples, using the SAVs specific for each formulation, gave excellent correlation (in millimoles per liter; r2 = 0.995) by the following equation: New Formulation = 1.02 (Old Formulation) -0.016; Sy.x = 0.074. The benefits of this approach to calibration include (1) accuracy is traceable to a reference method or methodologic principle and, wherever available, to reference materials; (2) new calibrator values (SAVs) can be assigned whenever the reagent formulation changes to maintain accurate patient results; and (3) if matrix effects are present, they will not adversely influence accuracy because traceability is based on patient sample comparisons.
Bias↗
Proficiency testing linked to the national reference system for the clinical laboratory: a proposal for achieving accuracy.
I propose using proficiency testing (PT) to achieve one of the important goals of CLIA: accurate and reliable clinical testing. Routine methods for the clinical laboratory are traceable to Definitive (DM) or Reference Methods (RM) or to Methodological Principles (MP) through a modification of the National Reference System for the Clinical Laboratory. PT is the link used to monitor consistent field performance. Although PT has been effective as a relative measure of laboratory performance, the technical limitations of PT fluids and of routine methods currently in use make it unlikely that PT alone can be used as a reliable measure of laboratory accuracy. Instead, I recommend calibration of routine systems through correlation to DM, RM, or MP with use of patients' specimens. The manufacturer is in the best position to assume this responsibility because of also being responsible for consistent, reliable product. Analysis of different manufactured batches of reagent would be compared with predetermined goals for precision and accuracy, as illustrated with data from product testing of Kodak Ektachem clinical chemistry slides. Adoption of this proposal would give manufacturers of PT materials, manufacturers of analytical systems, PT providers, and government agencies time to understand and resolve sources of error that limit the utility of PT for the job required by law.
Chemistry, Clinical↗
Bromocresol purple dye-binding method for the estimation of serum albumin adapted to the SMA 12/60.
We describe a method for the determination of serum albumin on the SMA 12/60 that utilizes the anionic dye bromocresol purple (BCP). This dye is more specific than the commonly used bromocresol green (BCG) in that it does not bind to globulins. The SMA module requires two simple changes for the BCP method to be adopted: a 600 nm interference filter replaces the 630 nm filter; and a gray-gray pump tube (rated at 1.00 mL/min) replaces a green-green tube (rated at 2.00 mL/min) in the predilution assembly. The precision of this method is comparable to the BCG method with a CV of 2.9% at mean values of 30.6 and 38.3 g/L. This method was compared to the BCP method of the DuPont aca using 51 patient samples over an approximate albumin range of 15 to 80 g/L. The correlation is very good as indicated in the linear regression data: (SMA) = 0.884(aca) + 3.46; coefficient of determination (r2) is 0.986; and standard error of the estimate (Sy.x) is 1.39 g/L. Neither hemoglobin nor bilirubin interferes with this BCP method up to levels of 9 g/L and 633 mumol/L, respectively.
Autoanalysis↗
Evaluation of a bromocresol purple method for the determination of albumin adapted to the DuPont aca discrete clinical analyzer.
We evaluated a new method for the determination of albumin on the DuPont aca discrete clinical analyzer that utilized an albumin selective dye, bromocresol purple (BCP). This dye minimizes globulin interference that occurs with bromocresol green (BCG) methods that have long (greater than 30 s) incubation times. Good correlation was observed between the new BCP method and two methods which do not show significant globulin interference: an immunological method and a rapid BCG method. Comparisons with alternate BCG methods (SMA 12/60, SMAC, and the aca) were generally not as good. The albumin results by the BCP method on specimens with elevated globulins were similar to results from the immunological and rapid BCG methods. The reference interval was 34-50 g/L. The between-day coefficient of variation ranged from 0.9 to 3.5% at three evaluation sites on 2 levels of 8 different control materials. The method was linear between 6-70 g/L. No interference was observed from hemoglobin at levels less than or equal to 5.00 g/L or from bilirubin at levels less than 342 mumol/L. Also, no interference was observed from nine common drugs that are known to bind to albumin. These studies show that accuracy, reproducibility and linearity of the BCP albumin method on the aca are acceptable for clinical use.
Autoanalysis↗
Changes in the pattern of drugs detected in a toxicology screen in an Upstate New York Hospital.
We analyzed the results from our clinical toxicology service over two consecutive 24-month periods from 1980 to 1983. The frequencies of drug or drugs detected, tabulated by patient and type of specimen submitted to the laboratory were studied. A toxicology screen or the identification of one drug was requested on 3328 patients in the 48 months of the study. Alcohol was the most frequently requested test--1221 requests in 1980 to 1981, and 627 in 1982 to 1983. Seventy-five percent of these requests were positive. Ethanol, in fact, accounted for 53 percent of all drugs detected in all specimens received. There were 989 requests for a drug screen (530 in 1980 to 1981, and 459 in 1982 to 1983) for which 1734 serum, urine, or gastric specimens were received. Serum or serum and urine were the most frequently submitted specimens. Gastric contents with or without a urine sample were sent least often. After alcohol, the most frequently detected drug classification was analgesic/antipyretic. The most dramatic change in prevalence was seen in over-the-counter stimulants which accounted for almost 11 percent of all drugs in 1982 to 1983, an increase from only 4 percent in 1980 to 1981. More than one drug per patient was found in 24 percent of the requests in 1982 to 1983; an increase from 18 percent in 1980 to 1981. We identified 81 different drug combinations in 1982 to 1983, up from 71 combinations in the first half of the study. Toxicology data may have significantly affected immediate therapy--either through the administration of an antidote or by initiation of aggressive intervention--in 7 percent of the patients whose specimens were analyzed in our laboratory. The laboratory technologist and the clinician should be cognizant of changing patterns of drug use to increase and maintain their effectiveness in the detection or treatment of drug intoxication. We have demonstrated that changes did occur in our facility over a 4-year period, and also when our data were compared to previous reports. Retrospective studies of this type are essential to meet those objectives.
Drug Combinations↗
Simultaneous analysis of antiarrhythmic drugs and metabolites by high performance liquid chromatography: interference studies and comparisons with other methods.
Our previously described HPLC method for the simultaneous analysis of several antiarrhythmic drugs and metabolites in serum [Clin. Biochem. 14. 113-118 (1981)] was correlated with an enzyme immunoassay technique (EMIT) for quinidine, procainamide, N-acetyl procainamide, and disopyramide. Correlation coefficients in each case was greater than 0.95. Our method compared favorably with a fluorescent procedure for the quantitation of propranolol in plasma. Interference studies with 34 drugs indicated that the measurements of quinidine and monodealkyldisopyramide were affected by quinine and lidocaine, respectively. Carbamazepine and glutethimide interfered with propranolol, but additional clean-up extractions removed these interferences.
Anti-Arrhythmia Agents↗
High performance liquid chromatographic analysis of the antiarrhythmic drugs procainamide, disopyramide, quinidine, propranolol and metabolites from serum extracts.
We describe a method for the simultaneous high performance liquid chromatographic determination of several antiarrhythmic drugs and some of their metabolites after extraction from 2.5 mL of spiked pooled sera. The extracts were applied to a C8 reversed phase column. Nine compounds of interest were resolved within the 30 minute run. An initial mobile phase of 80% phosphate (25 mmol/L, pH 3.5), 20% organic (acteonitrile:methanol, 2:3) was maintained for 2 min at which time a linear gradient was used to change the mobile phase to 30% phosphate, 70% organic at 20 min after injection. This composition was maintained from an additional 5 min. Absorbance at 212 nm was used for detection. Peak area ratios of drug to internal standard (N-propionylprocainamide) were used for quantitation. The relative standard deviations (and mean solute concentrations) of daily duplicate determinations for 15 days are: procainamide, 5.1% (5.9 mg/L); N-acetylprocainamide, 9.3% (6.0 mg/L); Mono-N-dealkyldisopyramide, 3.7% (4.1 mg/L); disopyramide, 4.3% (4.0 mg/L); quinidine, 4.5% (6.5 mg/L); and propranolol, 5.1% (0.097 mg/L). Dihydroquinidine and 4-hydroxypropranolol were also resolved but not quantitated.
Acecainide↗
Rate of achieving thermal equilibrium in two models of centrifugal analyzers.
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Centrifugation↗
Automatic loading of a centrifugal analyzer for enzyme immunoassays.
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Autoanalysis↗
Improved approach to sequential addition immunoassay.
In the usual sequential addition enzyme immunoassays for drugs, the activity of the drug-labeled enzyme decreases continuously with time as more of it is bound to antibody. Sensitivity also decreases; the activity immediately after mixing is the most sensitive indicator of drug concentration. The reaction of enzyme-drug with antibody can be stopped by saturating the antibody with a larger quantity of unlabeled drug, which reacts with the antibody faster than does the enzyme-labeled drug. When drug is added soon after the reaction starts, the enzyme activity is stabilized and the sensitivity to small quantities of antigen is increased. This approach, with modification, should be applicable to sequential immunoassays in which other kinds of labels are used. The enzyme activity can be measured for a longer time, with the predictable increase in precision, as well as the ability to detect smaller quantities, to use less reagent, and to use end-point rather than kinetic assays.
Antigen-Antibody Reactions↗
Enzyme immunoassays with the miniature centrifugal fast analyzer.
We studied the EMIT (Enzyme Multiplied Immunoassay Technique, Syva) procedures for the assay of phenytoin and phenobarbital in serum, adapting them to the miniature Centrifugal Fast Analyzer. For different concentrations of drug, each rate of reaction decreased continuously with time, tending to converge on a single common value. The rate was most affected by the concentration of drug almost immediately after the reagents were mixed, less so thereafter. The antibody evidently is present in sufficient excess to bind all the enzyme-labeled drug ordinarily present, but the antibody-bound enzyme was only 75% inhibited; this helps explain the appreciable residual activity when no drug is present. The reaction course was the same whether the serum and enzyme-labeled drug were added to the antibody sequentially or simultaneously, which suggests that antibody is bound to drug appreciably faster than to enzyme-labeled drug. The reaction rates 15 to 30 s after mixing were used as the measure of the drug concentrations. These results were confirmed by noting the rates at successive 15-s intervals. The analyzer yielded a run-to-run CV of 10% for phenobarbital at 30 mg/liter, and 9% for phenytoin at 15 mg/liter, as compared to the 15% quoted by Syva.
Centrifugation↗
Guinea pig intestinal iron binding protein.
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Amino Acids↗
Chelate mediated transfer of iron from transferrin to desferrioxamine.
Desferrioxamine, widely used for the treatment of iron overload in Cooley's anaemia, binds iron so tightly that it should quantitatively remove iron from transferrin. Studies conducted in vivo and in vitro, however, have failed to demonstrate significant depletion of transferrin-bound iron by a stoichiometric excess of desferrioxamine. However, low molecular weight chelating agents, capable of forming ternary complexes with transferrin and ferric iron, can promote a rapid transfer of iron from transferrin to desferrioxamine. A possible mechanism for this facilitated exchange is offered.
Chelating Agents↗
A new iron-binding protein isolated from intestinal mucosa.
A new iron-binding protein contained in guinea pig intestinal mucosa has been purified to homogeneity. The protein has a molecular weight of 78,000 in a nondissociating system and 43,000 in SDS-gel electrophoresis. It binds approximately 2 moles of iron per mole with a formation constant of 10(19) at pH 7. It is distinguished from transferrin and lactoferrin by differences on DEAE-Sephadex chromatography and spectroscopy and by its failure to cross-react with antisera to these other iron-binding proteins.
Animals↗