TDx Analyzer Research Articles

Effect of aminophylline upon the protective activity of common antiepileptic drugs and their plasma levels in mice.

Aminophylline (50 mg/kg) decreased the protective efficacy of carbamazepine (20 mg/kg), diphenylhydantoin (8-12 mg/kg), phenobarbital (20 and 25 mg/kg), and valproate (250 and 300 mg/kg) against electroconvulsions in mice. On the other hand, aminophylline (5 mg/kg) was devoid of such activity. Plasma levels of antiepileptic drugs were measured with the help of the Abbott TDx analyzer and after administration of carbamazepine (20 mg/kg), diphenylhydantoin (10 mg/kg), phenobarbital (25 mg/kg), and valproate (250 mg/kg) were as follows: 8.61, 6.48, 24.3 and 329 micrograms/ml, respectively. Aminophylline (50 mg/kg) remained without any significant influence upon these plasma levels. This may lead to the conclusion that aminophylline-induced reversal of antiepileptic drug activity is not dependent upon a pharmacokinetic mechanism and probably occurs at the neuronal level.

Detection of poisoning by plant-origin cardiac glycoside with the Abbott TDx analyzer.

Cardiac glycoside poisoning caused by ingestion of plant material is common in tropical and sub-tropical areas. In evaluating the use of the Abbott TDx Digoxin II assay to detect such cases of poisoning, we found it a rapid and convenient method for confirming the ingestion of glycosides from the plants Nerium oleander, Thevetia peruviana, and Adonis microcarpa, and from the toad Bufo marinus. Here we report some clinical cases illustrating our experience with the use of this assay, and describe results of cross-reactivity studies with compounds structurally similar to digoxin. Because of the competitive nature of the immunoassay as well as the complexity of the mixture of cross-reacting cardiac glycosides present in the plant material, the measured apparent digoxin concentration is not linearly related to the cardiac glycoside concentration.

Polarization fluoroimmunoassays for the specific determination of amphetamine and methamphetamine in urine with the abbott TD x-analyzer

Two polarization fluoroimmunoassays for the screening of amphetamine and methamphetamine in urine were adapted for use with the Abbott TD x-Analyzer running in the automatic mode. The detection limits of amphetamine and methamphetamine in 10 μl of urine were 0.03 and 0.05 mg l −1, respectively. These assays were specific for the determination of amphetamine (cross-reactivity with methamphetamine 1%) or for the determination of methamphetamine (cross-reactivity with amphetamine 2.5%). No significant cross-reaction was observed with other drugs of abuse (ephedrine, morphine and butabarbital).

Critical evaluation of the TDx Turbo Nephelometry System.

We critically evaluated the Nephelometry System (TDx Turbo) for the TDx Analyzer (Turbo), as currently used for immunoglobulins (IgA, IgG, and IgM) and transferrin assays. We describe hardware, software, reagent, and procedural changes made since the original publication (Clin Chem 1985;31:1474) and the mathematical treatment of data. The unit-dose format of the reagents allows for batch or panel testing of the analytes, with a throughput of 40 tests per hour. Measurements are made at pseudo-equilibrium, with sample-blank correction. The formulation of reagents and the assay scheme are such as to eliminate the need to check these assays for antigen excess. Assay sensitivities are 3% of the standard curve ranges. CVs are 8% for all assays. The system performance, when compared with rate nephelometry and radial immunodiffusion, yielded correlation coefficients of 0.97 or better for the analytes.

Evaluation of the TDx ® method for cyclosporine and a comparison to CYCLO-Trac ® RIA in renal transplant patients

The recent introduction of a fluorescence polarization immunoassay (FPIA) for cyclosporine by Abbott for their TDx analyzer provides an alternative to radioimmunoassay (RIA) and high performance liquid chromatography procedures. This new method is easier and faster than the Incstar CYCLO-Trac RIA assay. The TDx method has good precision except at low levels of cyclosporine. RIA gives consistently higher values than FPIA for samples containing only cyclosporine and in those from renal transplant patients. The FPIA procedure may be modified to allow up to a 50-min pause during the protein precipitation step, allowing more efficient use of technologists' time.

The Measurement of Amylase Using a Fluorescent Depolarization Assay on the Abbott TDx Analyzer

The performance of a fluorescence depolarization assay using the Abbott TDx analyzer for amylase activity in serum and urine samples was evaluated. Results obtained by the TDx method were compared with those obtained using the DuPont aca, the Kodak Ektachem, and the Roche Cobas-Bio analyzers. The interassay precision ranged from 4% to 7%. The linearity was verified up to 750 U/L of amylase. The correlation of patient amylase between the TDx and other comparative methods showed a correlation coefficient from 0.97 to 0.99. No interferences were found for bilirubin up to 340 μmol/L (20 mg/dL) and triglyceride up to 16 mmol/L (1,400 mg/dL). In general, the TDx amylase method provides a quick and reliable system for the measurement of amylase in serum and urine.

Total triiodothyronine by fluorescence polarization immunoassay (FPIA)

AbstractA semiautomated fluorescence polarization immunoassay (FPIA) for total T3 performed using the TDx analyzer has been evaluated. Precision of the assay at a low level of T3 (<1.0 ng/mL) is not good with CVs of about 17% observed. Precision at moderate to high levels (1.7–5.6 ng/mL) is good (CVs = 11.3−4.1%). Low end imprecision is attributable to a lack of sensitivity, with a reliable detection limit of only about 0.9 ng/mL. An average recovery of added T3 of 96% was noted, and the assay is not affected by interference due to lipemia, bilirubinemia, or hemolysis. A methods comparison study of the FPIA test and total T3 by RIA yielded a regression equation of Y = 1.08 × −.28, r = 0.95. The TDx FPIA total T3 test is a quick, semiautomated procedure, offering the advantage of a stable, stored calibration curve. It is useful for quantitating elevated levels of total T3 as found in hyperthyroid conditions, and its performance is comparable to or better than RIA procedures for this purpose. However, it cannot be recommended for the evaluation of patients with T3 values below 1.0 ng/mL, and RIA tests are still preferable for this analytical range.

Effect of albumin and lamellar bodies on fluorescence polarization of amniotic fluid.

Using a probe and procedure developed for the Abbott TDx analyzer, we investigated the influence of albumin on fluorescence polarization of amniotic fluid. Polarization readings increased when albumin was added to either "mature" or "immature" amniotic fluids. Albumin added to a fraction rich in lamellar bodies (10,000 X g pellet) greatly increased polarization readings, but albumin added to the lamellar-body-free fraction resulted in only small increases. Adding increasing amounts of the lamellar-body-rich fraction from mature and immature pools to a constant amount of albumin decreased the polarization readings. We saw no correlation between amniotic fluid polarization and albumin concentration but found a significant correlation between polarization values and either total extractable phospholipids (r = 0.725, P less than 0.001) or the ratio albumin/total extractable phospholipids (r = 0.784, P less than 0.001). The concentration of albumin in amniotic fluid was variable and correlated poorly with gestational age.

Improved fluorescence polarization assay for use in evaluating fetal lung maturity. III. Retrospective clinical evaluation and comparison with the lecithin/sphingomyelin ratio.

We clinically evaluated, retrospectively, our improved fluorescence polarization assay for fetal lung maturity. The procedure requires 0.5 mL of amniotic fluid and a standard clinical laboratory fluorescence polarimeter (TDx Analyzer, Abbott Laboratories). We measured the L/S ratios for 93 freshly collected amniotic fluids, uncontaminated with blood or meconium, collected within three days of delivery. The fluids were stored frozen for eight to 32 months, then thawed and assayed for net fluorescence polarization. Fourteen of the infants developed respiratory distress syndrome; five, transient tachypnea of the newborn; and 74, no respiratory distress. The polarization assay and lecithin/sphingomyelin ratio had equivalent receiver operating characteristic curves, indicating no difference in their clinical performance. Although a prospective study with fresh amniotic fluid specimens will be necessary to establish a definitive reference range, the present study shows that this assay can be used to rapidly predict fetal lung maturity.

Improved fluorescence polarization assay for use in evaluating fetal lung maturity. I. Development of the assay procedure.

We describe a fluorescence polarization assay for use in predicting fetal lung maturity, which is suitable for the TDx Analyzer (an automated fluorescence polarimeter). The assay requires 0.5 mL of amniotic fluid and approximately 30 min, and involves the fluorophore 1-palmitoyl-2(6-[(7-nitro-2, 1, 3-benzoxadiazol-4-yl)amino]caproyl) phosphatidylcholine. Reproducible polarization measurements depend on proper regulation of incubation time and temperature, but variations in the concentrations of fluorescent probe and amniotic fluid have little effect on measured polarization and therefore little effect on assay precision. Working solutions of the fluorescent probe are stable for at least nine months when stored at -20 degrees C and pH 5. Interferences include erythrocytes, serum, bilirubin, meconium, and lidocaine.

Reformulated REA ethanol assay evaluated.

In 1984, Abbott Laboratories introduced a radiative energy attenuation (REA) assay for the determination of ethanol on the TDX analyzer. The author's laboratory evaluated this method and compared its results with those obtained by a commonly used gas-liquid chromatographic (GLC) technique and the Du Pont aca. The REA method was found to be accurate, reproducible, and easy to use (1). Recently, Abbott reformulated the ethanol assay by replacing the iodonitrotetrazolium violet (INT) dye with thiazolyl blue (3-[4,5-dimethyl thiazol-2yl]-2,5-diphenyl tetrazolium bromide). The reason for this reformulation, according to the manufacturer, was to eliminate the probe wash protocol recommended after every run with the original REA ethanol assay. This wash, which used a 10% tetraethylammonium hydroxide solution, was necessary to remove small amounts of dye retained in the probe following the use of the INT-based assay. The introduction of the thiazolyl blue (MTT) notwithstanding, the Abbott REA ethanol assay using the linked enzymecatalytic reactions of alcohol dehydrogenase (EC 1.1.1.1) and diaphorase (EC 1.6.4.3, dihydrolipoamide reductase (NAD +)] is identical to the original assay. The reduced MTT yields a purple color with an absorbance peak at 565 nm which overlaps the excitation and emission spectrum of fluorescein (a fluorescent indicator added to the reaction having an excitation peak at 485 nm and an emission peak at 525 nm). The fluorescence intensity decreases logarithmically with increasing concentrations of reduced MTT making the concentration of ethanol proportional to the degree of inner filter effect on the fluorophore. The new REA formulation for determining ethanol was evaluated and its results compared with those obtained by GLC and an ethanol-specific enzymatic method performed on the Du Pont aca. Ethanol concentrations obtained by the MTT reagent system were also compared directly to results obtained by the original REA ethanol assay. The sample collection protocols and the analytical procedures used in this evaluation were identical to those used in the previous evaluation (1). Correlations between the various methods were determined by least-squares linear regression analysis of the experimentally obtained values using NWA Statpak | (Northwest Analytical, Inc.) on an Apple Macintosh TM computer (Apple Computer, Inc.).

Fluorescence depolarization assay for quantifying alpha-amylase in serum and urine.

We have developed a new method for quantifying alpha-amylase (EC 3.2.1.1) in serum and urine by fluorescence depolarization. Amylase in the sample catalyzes the hydrolysis of the substrate, a fluorescein-labeled amylose. This results in decreased fluorescence polarization, owing to the increased rate of rotation of the amylose fragment relative to the intact substrate. The TDx amylase assay is calibrated with six human-serum-based pancreatic amylase calibrators. Amylase activities are determined by interpolation from the calibration curve, which is stored in the TDx analyzer's memory. Results correlate well with those by the Du Pont aca assay and the Beckman "DRI-STAT" assay. Endogenous glucose does not interfere. CVs are less than 6%, and the reagents are stable in liquid form.

A nephelometry system for the Abbott TDx analyzer.

A self-contained light-scattering accessory carousel has been developed for the Abbott TDx fluorescence polarization analyzer, extending the instrument's capabilities to nephelometric methods of analysis, including assays for specific proteins by immunoprecipitation: IgG, IgA, IgM, and transferrin. The scattered light from a green-light-emitting diode (peak wavelength 565 nm) is measured at an angle of 37.5 degrees by the existing optical detection system of the TDx analyzer without modification of the instrument. Measurements are made at quasi-equilibrium, with sample blank correction. No sample pretreatment is required, and antigen-excess is checked automatically. CVs range from 3 to 6% (within-run) and 7 to 9%. (total). Calibration curves may be stored for at least two weeks. A nephelometric method for monitoring chromogenic reactions in the green wavelength region is also described. This method--Scattered Energy Attenuation (SEA)--has been used in preliminary experiments to measure calcium, total protein, iron, and bilirubin.

Evaluation of fluorescence polarization immunoassay for quantitation of serum salicylates.

A fluorescence polarization immunoassay (FPIA) for serum salicylates that has been developed for use with the Abbott TDx analyzer is evaluated with regard to precision, accuracy, and stability of the standard curve. The FPIA method is also compared with a well-established high performance liquid chromatography (HPLC) technique in a clinical laboratory environment. The FPIA demonstrates excellent precision, and the standard curve is sufficiently stable to perform reproducible measurements over a 29-day period without recalibration. Superior accuracy of the FPIA method is indicated for salicylate concentrations between 50 and 800 micrograms/ml by recovery studies and by favorable comparison with the reference method. The performance of the FPIA for salicylate concentrations between 0 and 50 micrograms/ml is somewhat less favorable and should be used with caution in this range. The present method is more appropriate than HPLC for the management of patients receiving chronic high doses of salicylates or in cases of acute salicylate overdose and is also more rapid.

Spurious phenobarbital levels by fluorescence polarization immunoassay using TDx analyzer in patients with renal disease.

Results of phenobarbital analyses are presented for 14 patients with chronic renal failure, and compared using gas-liquid chromatography (GLC), enzyme immunoassay (EIA), and fluorescence polarization immunoassay (FPIA). Correlation of FPIA with GLC and EIA was poor.