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Biomedical subjects

R E Cross

Publications and source records attributed to R E Cross.

16 recordsLinked to original sources
PubMed1989

Determination of N-desmethylmethsuximide serum concentrations using enzyme-multiplied and fluorescence polarization immunoassays.

N-Desmethylmethsuximide (NDM), the active metabolite of the antiepileptic agent methsuximide, has been analyzed by gas-liquid chromatography and high-performance liquid chromatography (HPLC) in the past. This study compares methods using two commercially available immunoassays for ethosuximide, the enzyme multiplied immunoassay technique (EMIT) and fluorescence polarization immunoassay (FPIA), with an HPLC method for the measurement of NDM concentrations in serum. Within-day precision studies, utilizing low therapeutic (15.0 mg/L) and toxic (45.0 mg/L) NDM concentrations (n = 20), resulted in coefficients of variation (CVs) of 4.6 and 4.2%, respectively, for EMIT and 5.4 and 3.2%, respectively, for FPIA. Day-to-day precision studies (n = 10) resulted in CVs of 7.6 and 5.5%, respectively, for EMIT and 3.5 and 2.4%, respectively, for FPIA. No interference was observed from toxic concentrations of acetaminophen, caffeine, carbamazepine, methsuximide, phenobarbital, phensuximide, phenytoin, primidone, salicylate, and valproic acid in the EMIT and FPIA procedures. There was good linear correlation between EMIT and HPLC NDM determinations of 50 patient samples (r = 0.970; y = 0.96 x + 0.03), and a similar correlation between FPIA and HPLC NDM determinations in 48 patient samples (r = 0.975; y = 0.91 x + 1.24). Using ethosuximide reagents, both EMIT and FPIA systems can be adapted to reliably measure NDM serum concentrations.

Chromatography, High Pressure Liquid↗
PubMed1986

Chromium deficiency after long-term total parenteral nutrition.

A 63-year-old female developed unexplained hyperglycemia and glycosuria during administration of a total parenteral nutrition regimen on which she had been stable for several months. Because the patient had no history of diabetes or evidence of an infection, chromium deficiency was considered. Plasma chromium level was 0.1 microgram/dl (laboratory reference interval: 1.8-3.8 micrograms/dl). Fourteen days of supplemental intravenous chromium chloride (200 micrograms/day) allowed complete withdrawal of exogenous insulin with no further hyperglycemia or glycosuria. Correction of unexplained glucose intolerance following vigorous chromium supplementation indicates that the patient had chromium deficiency. Subsequent plasma chromium levels remained unchanged, possibly reflecting the sensitivity limits of the assay that was used, the uncertainty that exists regarding appropriate reference intervals for this element, and the fact that plasma levels do not always correlate with total body stores. The patient did not manifest peripheral neuropathy, which was present in one of the two previously reported cases, nor encephalopathy, which was reported in the other. We conclude that this patient developed chromium deficiency as a result of inadequate administration of chromium in the parenteral formula (6 micrograms/day) plus excessive enteric losses, and she presented with glucose intolerance as the only clinical manifestation of the deficiency. Caution should be exercised when interpreting plasma chromium in patients with suspected deficiency.

Blood Glucose↗
PubMed1985

DNA relationships among some tox-bearing corynebacteriophages.

The DNA genomes of a number of tox-bearing, temperate corynebacteriophages isolated from strains of Corynebacterium diphtheriae and Corynebacterium ulcerans were compared. With one exception, these phages displayed similarities in their restriction enzyme digest profiles and extensive homology with prototypic beta converting phage. The exception, phage delta, had a unique restriction profile and exhibited homology with beta over a limited portion of its genome. DNAs of phages from each host contained cohesive ends and integrated as prophage by a mechanism analogous to that employed by coliphage lambda. It is proposed that these tox-bearing phages belong to a common family, the beta family. The role of the beta family in the movement of the tox gene between strains of C. diphtheriae and C. ulcerans is discussed.

Bacteriophages↗
PubMed1977

Enzyme-coupled measurement of uric acid in serum with a centrifugal analyzer.

An early-reading blank-corrected end-point determination of uric acid in serum has been developed for use with a centrifugal analyzer. The method is based on a modification of the uricase (urate:oxygen oxidoreductase, EC 1.7.3.3)/catalase (hydrogen peroxide:hydrogen peroxide oxidoreductase EC 1.11.1.6)/aldehyde dehydrogenase (aldehyde:NAD(P)+ oxidoreductase, EC 1.2.1.5)-coupled analytical scheme reported by Haeckel [Z. Klin. Chem. Klin. Biochem. 14, 101 (1976)]. Sensitivity and precision of the method are excellent, and results compare well with those obtained by the Kageyama procedure [Clin. Chim. Acta 31, 421 (1971)].

Aldehyde Oxidoreductases↗
PubMed1977

Adaptation to the centrifugal analyzer of an enzymatic method for the measurement of lactate in plasma and cerebrospinal fluid.

A fully enzymatic method for measurement of l(+)-lactate has been adapted for use with a centrifugal analyzer. The procedure is based on a two-point fixed-time kinetic approach for elimination of static interferences, and commercially available reagents are used. Specimen collection and preservation are simplified by the use of standard evacuated tubes containing sodium fluoride. Under these conditions lactate is stable for as long as seven days at 4 degrees C, and deproteinization is unnecessary. The method is extremely simple and ideally suited for emergency and routine use. Determinations may be performed on plasma or cerebrospinal fluid. Sensitivity and precision are excellent, linearity extends to 8.0 mmol/liter, and results compare well with those obtained using the manual enzymatic procedure.

Alanine Transaminase↗
PubMed1976

An integrated approach to lipid profiling: enzymatic determination of cholesterol and triglycerides with a centrifugal analyzer.

We describe enzymatic methods for determination of cholesterol and triglycerides (triacylglycerols), adapted for use with a centrifugal analyzer. Triglycerides are determined by a two-point kinetic method, which utilizes a single glycerol standard for calibration and provides for a within-run reagent blank correction. The endpoint determination of cholesterol combines the unique blanking capabilities of the centrifugal analyzer to correct for sample and reagent blank interferences. Results correlate well with those obtained by procedures standardized by the Lipid Research Clinics Program for use with a continuous-flow system.

Autoanalysis↗
PubMed1976

Improved method for measurement of inorganic phosphate in serum with a centrifugal analyzer.

A direct mehtod [Clin. Chim. Acta 46, 113 (1973)] for determination of inorganic phosphate in serum was adapted for use with a centrifugal analyzer. Contamination is minimized and analysis rate maximized by doing the reaction in the reagent wells of the transfer disc and by utilizing the high-speed spectrophotometric and data-reduction capabilities of the centrifugal analyzer. Hemolysis, icterus, and moderate lipemia cause no interference. Grossly lipemic sera and sera from patients with plasma cell dyscrasias can be analyzed by incorporating appropriate blanking and dilution techniques. The method exhibits excellent sensitivity and precision and results correlate well with those from a continuous-flow procedure.

Autoanalysis↗
PubMed1976

Adaptation of blank-corrected methods for measurement of total and conjugated bilirubin and uric acid to the centrifugal analyzer.

The blank-corrected determination in serum of total and conjugated bilirubin and of uric acid has been adapted to the centrifugal analyzer. Bilirubin is measured by a modified Jendrassik and Grof procedure; uric acid is determined kinetically by using a reaction based on reduction of ferric ion, including a uricase-treated blank. Sensitivity and precision of both methods are excellent, and results compare well with those obtained by commonly used procedures.

Autoanalysis↗
PubMed1975

Evaluation of kinetic light scattering as an approach to the measurement of specific proteins with the centrifugal analyzer. I. Methodology.

A laser-modified centrifugal analyzer was used to develop kinetic light scattering methods for the measurement of human immunoglobulins IgG, IgA, and IgM. Comparison of equilibrium light scattering methods with kinetic procedures for IgG and IgA demonstrate equivalent precision and relative accuracy. However, quantitative results obtained by equilibrium and kinetics methods for IgM were found to differ significantly. Recovery studies performed with purified IgM have shown that both methods can yield quantitative results in the normal range. Our observations demonstrate that the technique offers a viable and in some respects a superior alternative to other methods currently used in the clinical laboratory.

Autoanalysis↗
PubMedDate not supplied

Rapid enzymatic determination of amylase in serum and urine using a centrifugal analyzer.

A convenient, totally enzymatic procedure for amylase assay using a centrifugal analyzer is described. The reaction scheme is examined using both starch and maltotetroase as substrates. Data for the reaction kinetics, linearity and sensitivity are presented. The proposed method exhibits linear reaction kinetics between three and five minutes after the initiation of the reaction and is linear to 1200 U per liter of amylase. The determination is rapid, (five minutes analysis time), convenient, (only one reagent), and precise, (1.2% within-day C.V. and 4.6% day-to-day C.V.), at a level of 62 U per liter. The proposed method compares favorably with chromogenic procedures; (r = 0.979, n = 84).

Amylases↗