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C N Ou

Publications and source records attributed to C N Ou.

At least 73 records · Page 4Linked to original sources
PubMed1986

Liquid chromatography used in diagnosis of a rare hemoglobin combination: hemoglobin S/LeporeBoston.

"High-performance" liquid chromatography (HPLC), applied to hemoglobin analysis, is decidely more sensitive and gives better resolution than do routine electrophoretic methods. Here we present a case with a rare double heterozygote hemoglobin S/LeporeBoston, originally diagnosed as homozygous hemoglobin S by routine electrophoretic methods. Using a gradient elution weak cation-exchange HPLC technique, we could separate hemoglobin S and hemoglobin LeporeBoston and make the correct diagnosis. This case demonstrates how HPLC can be a useful adjunct to routine electrophoresis.

Adult↗
PubMed1986

Measurement of total bilirubin by use of bilirubin oxidase.

We used an enzymatic method for measuring total bilirubin in serum. Results by this method varied linearly with bilirubin concentrations to at least 300 mg/L. The day-to-day precision (CV) of the method ranged from less than 1% to about 11% at bilirubin concentrations of 183 and 12 mg/L, respectively. Commonly used anticoagulants, serum preparation materials, and selected drugs had no effect on the apparent bilirubin concentration, but turbidity caused a slight increase and hemoglobin concentrations of 2 g/L resulted in lower values, by as much as 17 mg/L at a bilirubin concentration of 95 mg/L. Patients' results obtained with this enzymatic method were slightly lower than those obtained with methods based on the Jendrassik-Grof principle. The largest differences, seen in samples with high "direct" bilirubin concentrations, can be decreased by measuring the absorbance at 425 nm instead of at 465 nm as recommended by the supplier of the bilirubin oxidase method.

Adult↗
PubMed1985

Enzymatic measurement of serum glycerol using a COBAS-BIO centrifugal analyzer.

An enzymatic method for the measurement of glycerol using glycerol kinase coupled to pyruvate kinase and lactate dehydrogenase was adapted to a COBAS-BIO centrifugal analyzer. Routine standardization is not required under the optimized conditions since the calculation factor derived from the measurement of pure glycerol standard was found to be identical to the theoretical value. Excellent correlation between the method and the DuPont ACA triglyceride method was obtained. The coefficients of variation for within-run and day-to-day precision were less than 4%. Only 2 microL of serum is required, making this an excellent means for monitoring therapeutic glycerol administration in premature infants with hydrocephalus. The method has the sensitivity to measure glycerol concentrations as low as 0.1 mmol/L. This, together with the rapid analysis time (28 specimens in 10 min), makes it suitable for the correction of glycerol interference in the measurement of serum triglyceride.

Centrifugation↗
PubMed1985

High-performance liquid chromatography in the diagnosis of hemoglobinopathies and thalassemias. Report of three cases.

High-performance liquid chromatography is a technic that has recently been applied to the diagnosis of hemoglobinopathies and thalassemias. Its advantages over other methods include increased sensitivity, resolution and simplicity, as well as speed. In this report, the authors present an HPLC procedure that uses a weak cation exchange column and a gradient elution system for the diagnosis of hemoglobinopathies and thalassemias. The authors illustrate the utility of this procedure by reporting three cases in which the technic enabled them to make the correct diagnosis, which by traditional methods would have been missed or equivocal.

Child↗
PubMed1985

Unconjugated hyperbilirubinemia is overestimated in neonates with cholestasis. A more reliable method is proposed.

Unconjugated bilirubin was determined in 458 serum samples from 160 neonatal and pediatric patients by using two approaches. The first approach was to calculate indirect bilirubin by subtracting direct bilirubin, as measured by a diazo solution assay, from total bilirubin quantified by a Jendrassik-Grof procedure. The second approach was actually to measure the unconjugated bilirubin fraction using a multilayered slide. For samples containing little or no conjugated bilirubin, correlation between the calculated indirect bilirubin value and the unconjugated bilirubin measured by the slide was judged acceptable. Samples containing increased levels of conjugated bilirubin, however, yielded discrepancies between the approaches including differences of up to 5-10 mg/dL and more. Moreover, the magnitudes of the differences correlated with the amounts of conjugated bilirubin present in the samples. The unconjugated bilirubin values given by the slide were found to correlate more closely than the calculated indirect values with results obtained by an HPLC procedure that may be regarded as the most reliable method available. Therefore, we find that the slide provides a more accurate measure of unconjugated bilirubin than does the indirect bilirubin value in specimens from pediatric patients having evidence of cholestasis. The authors also believe that the magnitude of the difference in the values could make a difference in therapeutic strategies.

Age Factors↗
PubMed1984

Evaluation of the Kodak EKTACHEM clinical chemistry slide for the measurement of bilirubin in newborns.

Measurement of neonatal bilirubin using the Jendrassik-Grof method (x) and the EKTACHEM NBIL assay (y) was compared over a 6-month period in a total of 1191 specimens from 483 patients less than 30 days of age. Linear regression analysis of the data yields a slope of 0.937, an intercept of 0.387, and Sy,x of 0.55 and a correlation coefficient of 0.983 for a total of 1032 specimens from patients less than or equal to 14 days of age and a slope of 1.090, an intercept of 0.002, an Sy,x of 1.03 and a correlation coefficient of 0.950 for a total of 159 specimens from patients greater than 14 days of age. The best correlation between EKTACHEM NBIL assay and the reference Jendrassik-Grof method was observed in samples from patients less than or equal to 14 days of age. Data from patients older than 14 days showed a higher proportional bias and a lower correlation coefficient between the methods. High performance liquid chromatographic analysis demonstrated that patients greater than 14 days of age had a higher incidence of elevated delta-bilirubin. Linearity extends to 200 mg/l. The NBIL assay provides a rapid, precise micromethod that is less sensitive than the Jendrassik-Grof method to the in vitro photo degradation of bilirubin and is not subject to the interference from hemoglobin and lipids. Because delta-bilirubin is not measured by this method, it is only recommended for newborns less than or equal to 14 days of age.

Bilirubin↗
PubMed1984

Evaluation of the EMIT reagent system for measurement of caffeine with the EMIT Lab 5000 System and a centrifugal analyzer.

Using a Syva EMIT Lab 5000 System, we evaluated a newly developed EMIT assay for measurement of caffeine in serum of neonates. The method is rapid, and coefficients of variation for within-run and day-to-day precision were less than 5%. The accuracy of the method, as evaluated from analytical recovery and a calibrator-crossover study, is excellent. Comparison of the results analyzed by the EMIT caffeine assay (y) and the liquid-chromatographic comparison method (x) yielded the linear regression equation y = 1. 052x + 0.293 (n = 110, r = 0.987, and Sy . x = 0.625). The method was also adapted to a COBAS-BIO centrifugal analyzer (y) and optimized to minimize sample and reagent consumption. Linear regression analysis yielded the equation y = 1. 031x + 0.227 (n = 61, r = 0.992, and Sy . x = 0.488). As many as 400 assays per EMIT kit can be performed with the analyzer method, with excellent precision and accuracy. The kit assay and this centrifugal analyzer are well suited for rapid batch testing: 28 analyses (including six calibrators) in 10 min.

Adult↗
PubMed1984

Simultaneous measurement of ethosuximide, primidone, phenobarbital, phenytoin, carbamazepine, and their bioactive metabolites by liquid chromatography.

A simple, isocratic liquid-chromatographic method was developed for simultaneously measuring ethosuximide, primidone, phenobarbital, phenytoin, carbamazepine, and their bioactive metabolites within 10 min. The chromatographic system involves a Waters' Radial-NOVA PAK C18 reversed-phase column and acetone/methanol/acetonitrile/10 mmol/L phosphate buffer (10/21/8/61 by vol, pH adjusted to 7.95 with NaOH) as mobile phase. The antiepileptic drugs are extracted from 50 microL of serum by mixing with 50 microL of acetonitrile containing 10 mg of tolybarb per liter as internal standard. After centrifugation, 20 microL of the supernate is injected onto the column and eluted with mobile phase at the rate of 2.8 mL/min at ambient temperature. The column effluent is monitored at 200 nm. The method can detect the five antiepileptic drugs in concentrations as low as 0.5 mg/L. Analytical recovery ranges from 98 to 102%. Within-run CV ranged from 2.9 to 5.8% and between-run CV from 4.7 to 7.1%. The method can also be used to measure N-desmethyl-methsuximide, chloramphenicol, and pentobarbital.

Anticonvulsants↗
PubMed1984

Particle-enhanced turbidimetric inhibition immunoassay for theophylline evaluated with the Du Pont aca.

We evaluated the Du Pont Particle-Enhanced Turbidimetric Inhibition Immunoassay (PETINIA) for theophylline. The imprecision (CV) of the assay was less than 4.7% between-run and less than 3.6% within-run for theophylline concentrations between 5 and 30 mg/L. Standard curves for the assay were linear for theophylline concentrations from 0 to 46 mg/L and were stable throughout the study (i.e., for at least three months). The monoclonal antibody against theophylline used in this assay increases specificity; of the possibly interfering drugs, metabolites, and anticoagulants tested, only 1,3-dimethyluric acid and EDTA showed measurable effects. Bilirubin (less than 300 mg/L), hemoglobin (less than 6 g/L), or lipemia (triglycerides less than 6 g/L) does affect the quality of the assay. Analytical recovery of theophylline added to serum (5 to 40 mg/L) averaged 98% (range 93% to 112%). Comparison of results for patients' sera by the PETINIA method with those by enzyme immunoassay (EMIT) and by "high-performance" liquid chromatography yielded slopes and intercepts not significantly different from 1.0 and 0.0, respectively, and correlation coefficients ranging from 0.986 to 0.995.

Autoanalysis↗
PubMed1984

Liquid-chromatographic determination of indomethacin in blood from newborns with patent ductus arteriosus.

This rapid, accurate "high-performance" liquid-chromatographic procedure is intended for measuring indomethacin in serum from neonates who are receiving indomethacin for symptomatic patent ductus arteriosus. Indomethacin and an internal standard (flufenamic acid) are extracted from serum or plasma with chloroform or diethyl ether at pH 5.0. For the chromatography we used a Waters' Radial Compression Separation System (Radial-NOVA PAK C18 reversed-phase column) and a mobile phase of methanol/sodium acetate buffer (10 mmol/L, pH 3.6), 70/30 by vol. The column effluent is monitored at 254 nm. Both indomethacin and flufenamic acid are eluted within 7 min. Indomethacin can be detected in concentrations as low as 50 micrograms/L, in 100-microL samples. Response varies linearly with indomethacin concentration to at least 2 mg/L. Analytical recovery is 75%; relative recovery is 100%. Precision is excellent. Using this method, we were able to improve the success rate for pharmacological management of symptomatic patent ductus arteriosus, especially in neonates with fast clearance rates for the drug.

Chromatography, High Pressure Liquid↗
PubMed1983

High-performance liquid chromatography of human hemoglobins on a new cation exchanger.

We have investigated the use of a high-performance liquid chromatographic (HPLC) column packed with a unique weak cation exchanger prepared by coating silica with poly(aspartic acid) for hemoglobin analysis. The complete separation of hemoglobin Bart's F, A0, A2, S, C, D, E, G, SG, Winnipeg and Sealy was achieved by gradient elution within 30 min. The high resolution made it possible to distinguish hemoglobin variants such as Bart's, AC, AD, AE, AG, AS, ASG, CC, SC, SS, Winnipeg, Sealy and beta-chain variants with thalassemia such as S/beta +, S/beta 0 and S(C)-beta + thalassemia. Comparison of DEAE-cellulose column chromatography and our HPLC method for the quantitation of hemoglobin A2 yielded a good correlation. Hemoglobins A2, C and E are completely resolved on PolyCAT A columns in contrast to both cellulose acetate electrophoresis and DEAE-cellulose column chromatography. The high resolution of the system and the accuracy of the method combined with complete automation make this procedure useful for diagnosis of hemoglobin disorders in both a research and clinical laboratory environment.

Adult↗
PubMed1983

Concurrent measurement of theophylline and caffeine in neonates by an interference-free liquid-chromatographic method.

A sensitive liquid-chromatographic method was developed for the simultaneous measurement of theophylline and caffeine within 6 min. The excellent resolution of the method allows the complete separation of theophylline, internal standard, and caffeine from frequently encountered interfering drugs including acetaminophen, acetazolamide, acetylsalicylate, ampicillin, 8-chlorotheophylline, cefazolin, cephalosporin C, cephalothin, cephapirin, chloramphenicol, dyphylline, metronidazole, 3-methylxanthine, salicylate, sulfadiazine, sulfamerizine, sulfamethazine, sulfamethoxazole, sulfisoxazole, and theobromine. The chromatographic system involves a Waters' Radial-Pak C18 reversed-phase column and acetonitrile in 0.1 mol/L potassium phosphate buffer, pH 4.0, (9.5/90.5 by vol) as the mobile phase. The method can detect theophylline or caffeine concentrations as low as 0.5 mg/L in 50 microL of serum. Precision and accuracy are excellent.

Caffeine↗
PubMed1982

Theophylline, dyphylline, caffeine, acetaminophen, salicylate, acetylsalicylate, procainamide, and N-acetylprocainamide determined in serum with a single liquid-chromatographic assay.

We describe a single set of liquid-chromatographic conditions for assay of theophylline, dyphylline, caffeine, acetaminophen, salicylate, acetylsalicylate, procainamide, and N-acetylprocainamide in serum. The chromatographic system includes a Waters Associates mu-Bondapak C18 column and acetonitrile in 0.1 mol/L potassium phosphate buffer, pH 4.0 (9.75/90.25 by vol), as the mobile phase. Only 50 microL of serum is required, and drug concentrations as low as 0.5 mg/L can be detected. Absolute and relative analytical recoveries range from 95 to 101%. Day-to-day variation of the method is less than 6% for each drug. Linearity extends to 1 g/L for all drugs. Recycling of the mobile phase under pressure eliminates the need to prepare and de-gas solvents. The use of the single stationary and mobile phase provides a practical and economical approach to routine and urgent therapeutic drug monitoring.

Acecainide↗
PubMed1981

Liquid-chromatographic analysis for urinary porphyrins.

Urinary porphyrins are separated, according to number of carboxyl groups, in a system consisting of a mu-Bondapak C18 stationary phase and a mobile phase of methanol and aqueous sodium phosphate (pH 3.5) in a linear gradient. The specimen is prepared simply by adjusting the pH of a 5-mL sample to 2.0 and removing solids by centrifugation. The eluted porphyrins are measured fluorometrically. Naturally occurring non-porphyrin fluorescent substances are eluted ahead of the porphyrins. Chromatography requires about 20 min, and a re-establishment of initial conditions requires an additional 15 min.

Adult↗
PubMed1980

Assay for erythrocyte uroporphyrinogen I synthase activity, with porphobilinogen as substrate.

We describe a convenient, economical procedure for measuring uroporphyrinogen I synthase (EC 4.3 1.8) activity in erythrocytes, the results of which can be used to diagnose acute intermittent porphyria, in either its latent or acute stage. By limiting the test reaction sequence to the conversion of porphobilinogen to porphyrins, we eliminated several disadvantages of alternative methods in which delta-aminolevulinate is used as substrate. The latter assay was inhibited by lead; our procedure was not. Our procedure also gave greater porphyrin synthesis with less substrate. Erythrocytes of healthy women presented a mean activity of 12.4 nmol of porphyrin formed per liter per second; erythrocytes of healthy men presented a mean activity of 11.0 nmol/L per second. The within-run coefficient of variation (CV) for our assay was 1.8%; the between-run CV was 3.1%.

Ammonia-Lyases↗