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Biomedical subjects

R H Ng

Publications and source records attributed to R H Ng.

At least 37 records · Page 2Linked to original sources
PubMed1985

The Technicon RA-1000 evaluated for measuring sodium, potassium, chloride, and carbon dioxide.

We evaluated the Technicon RA-1000 "random-access" analyzer for the measurements of sodium, potassium, and carbon dioxide by an indirect potentiometric method (ion-selective electrode) and for chloride by a colorimetric method (mercuric thiocyanate). For various concentrations of control materials the total precision (CV) ranged from 0.9 to 1.2% for sodium, 1.1 to 1.3% for potassium, 1.0 to 1.2% for chloride, and 2.8 to 3.8% for carbon dioxide. The system demonstrated acceptable performance in linearity and carryover. Patients' results from the RA-1000 correlated well with those from the Beckman ASTRA-8. In a study on potential interferences, we found that high concentrations of salicylate and bromide significantly affected measurements of carbon dioxide and chloride, respectively. The RA-1000 requires only 30 microL of sample for all four tests and it offers a high throughout (30 specimens analyzed for the four tests in 25 min). This precise, easy-to-use, random-access analyzer requires minimal maintenance.

Autoanalysis↗
PubMed1985

Performance of five thyroid-function tests by radioimmunoassays with antibodies attached to paramagnetic micro-particles.

We have assessed the analytical and clinical performance of five thyroid-function tests by commercially available radioimmunoassays in which antibodies attached to paramagnetic micro-particles are used (Corning MAGIC assays). We evaluated the methods for measuring thyroxin, triiodothyronine, triiodothyronine uptake, thyrotropin (thyroid-stimulating hormone), and free thyroxin. Precision, patients' results, and clinical correlation of the MAGIC assays were similar to those of the well-established RIAs used as the comparative methods in this study; the MAGIC assays, however, are much faster and easier to perform.

Evaluation Studies as Topic↗
PubMed1985

Determinations of immunoglobulins G, A, and M in the Technicon RA-1000.

We evaluated the Technicon RA-1000 "Random Access" analyzer for the measurements of immunoglobulins G, A, and M in serum by turbidimetry. For various concentrations of serum pools the total CV ranged from 3.0 to 4.5% for IgG, from 3.1 to 3.2% for IgA, and from 4.8 to 5.4% for IgM. The linearity of the standard curves was good in the clinically useful ranges. Results for patients' samples correlated well with those determined with the Beckman Auto ICS (rate nephelometric method). Normal reference intervals (based on data for 200 healthy blood donors) are 7.67 to 16.87 g/L for IgG, 0.87 to 3.89 g/L for IgA, and 0.61 to 2.70 g/L for IgM. The RA-1000 requires only 8 microL for all three tests and can analyze 25 specimens for all three proteins in 37 min. Compared with other methods for immunoglobulin assays, the RA-1000 has higher throughput and offers significant savings in labor and reagent costs.

Autoanalysis↗
PubMed1985

Increased activity of creatine kinase isoenzyme MB in a theophylline-intoxicated patient.

A 78-year-old woman had increased activities of creatine kinase (CK; EC 2.7.3.2) and CK-MB isoenzyme in her serum, associated with severe theophylline intoxication. The time course for CK-MB activity was similar to that from an acute myocardial infarction. Clinical findings, however, including electrocardiograms, did not support the diagnosis of myocardial infarction. We suggest caution in interpreting CK-MB results in severe theophylline intoxication.

Aged↗
PubMed1984

Collection and handling of 24-hour urine specimens for measurement of analytes related to renal calculi.

Analysis for calcium, magnesium, phosphorus, oxalate, uric acid, and creatinine in 24-h urine collections is often needed for the differential diagnosis of patients with renal calculi. Considerable attention has been given to improving the methods of analysis, but improper sample collection and processing can cause significant errors for calcium and oxalate in urine samples not treated with acid and for uric acid in urine samples not treated with base. The errors are related to the concentration of the analyte, the interval the sample is stored before analysis, and the original pH of the urine sample. We describe here a system of sequential acidification (to pH 1.5) and alkalinization (to pH 9) of 24-h urine samples, followed by heating at 56 degrees C for 10 min. This procedure allows accurate analysis for all the above analytes in the same 24-h collection of urine. We validated the sample-treatment protocol for 80 24-h urine collections.

Calcium↗
PubMed1983

Regulation of bacterial glycogen synthesis. Stimulation of glycogen synthesis by endogenous and exogenous cyclic adenosine 3':5'-monophosphate in Escherichia coli and the requirement for a functional CRP gene.

In Escherichia coli cya mutants, deficient in adenylate cyclase (EC 4.6.1.1), basal cellular rates of glycogen synthesis were lower and the relative increases produced by exogenous cyclic adenosine 3',5'-monophosphate during growth on glucose were greater than in their respective parent strains. These observations provide strong evidence that endogenous cyclic AMP is one of the key regulators of glycogen synthesis in growing E. coli. In crp mutants, deficient in cyclic AMP receptor protein (CRP), the basal cellular rates of glycogen synthesis were much lower than in their respective parent strains. Stimulation of glycogen synthesis by exogenous cyclic AMP was markedly attenuated in the three crp mutants. Thus, stimulation of glycogen synthesis by either endogenous or exogenous cyclic AMP appears to require CRP. Functional CRP appeared to be required for all three responses observed after cyclic AMP addition: an abrupt step-up in the cellular rate of glycogen synthesis, a continuing exponential increase in rate, and a stimulation of the rate during a subsequent nitrogen starvation. To account for these responses, we derived a mathematical model in which the cyclic AMP-CRP complex regulates the differential rate of synthesis of an enzyme metabolizing an effector of the rate-limiting enzyme of glycogen synthesis.

Cyclic AMP↗
PubMed1983

Three commercial methods for serum ferritin compared and the high-dose "hook effect" eliminated.

We evaluated four commercial kits for measuring serum ferritin, based on three techniques: immunoradiometric assay, radioimmunoassay, and enzyme immunoassay. The kits evaluated were those manufactured by Abbott Laboratories, Clinical Assays, Corning Medical, and Ramco. Two of the immunoradiometric kits showed satisfactory results with respect to sensitivity and precision; they should be useful in diagnosing individuals with uncomplicated iron-deficiency anemia. One of the immunoradiometric assay kits, however, showed a high-dose "hook effect," beginning at 10 mg of ferritin per liter. We modified this kit to eliminate this effect, at least to ferritin concentrations of 33 mg/L. (We observed a ferritin value as high as 47 mg/L in one patient.) Results with all these kits did not inter-compare well for ferritin concentrations greater than 300 micrograms/L, a finding that casts further doubt on the controversial use of serum ferritin measurement in cases of iron overload.

Anemia, Hypochromic↗
PubMed1983

Interference by hemolysis with various methods for total calcium and its correction by trichloroacetic acid precipitation.

We evaluated the influence of hemolysis on total serum calcium as determined with the Du Pont aca, SMA 12/60, Ektachem 400, Corning 940 EGTA titrator, and the Beckman Astra 8, comparing results with those obtained by atomic absorption spectroscopy. We find that hemoglobin does not influence calcium measurements with the SMA 12/60, Ektachem 400, or Beckman Astra 8. The presence of hemoglobin exceeding 2 to 3 g/L caused falsely high results with the aca and falsely low results with the Corning 940 titrator. Similar interferences may be observed with other titrating or colorimetric procedures that involve direct reaction of the sample with o-cresolphthalein complexone or calcein. Upon removal of the hemoglobin by precipitation with trichloroacetic acid, the values obtained with the aca and the Corning 940 EGTA titrator were similar to those measured by atomic absorption. With nonhemolyzed serum samples the acid treatment had little or no effect on the aca procedure but resulted in a positive bias of approximately 10% with the EGTA procedure. Thus we recommend this trichloroacetic acid procedure for measuring calcium in hemolyzed samples with the aca and, with certain reservations, with the EGTA titrator.

Autoanalysis↗
PubMed1981

Inhibition by neurotoxic phospholipases A2 of synaptosomal uptake of gamma-aminobutyric acid.

A comparison has been made of the abilities of several neurotoxic and nontoxic phospholipases A2 from snake venoms to inhibit the intake of gamma-aminobutyric acid into synaptosomes from rat cerebral cortex. The neurotoxic phospholipase A2 inhibited GABA uptake more than the nontoxic enzymes did. However, there was a poor correlation between the measured specific enzyme activity of a phospholipase A2 and its ability to inhibit the uptake of GABA.

Animals↗
PubMed1980

Mitochondria and sarcoplasmic reticulum as model targets for neurotoxic and myotoxic phospholipases A2.

Certain neurotoxins and myotoxins from snake venoms have phospholipase A(2) activity (phosphatide 2-acylhydrolase, EC 3.1.1.4), which appears to be necessary for their toxicity. Several of these toxins inhibit the net uptake of Ca(2+) into sarcoplasmic reticulum vesicles and brain mitochondria. We have obtained evidence that the ability to inhibit this Ca(2+) uptake is a mechanistically relevant correlate of the toxicity of these proteins rather than being just a nonspecific consequence of their phospholipase A(2) activity. Two of the toxins, beta-bungarotoxin and notexin, had 5% and 50%, respectively, of the phospholipase A(2) activity of IVa phospholipase A(2)(a nontoxic enzyme), but beta-bungarotoxin was as effective as IVa in inhibiting Ca(2+) uptake into brain mitochondria and notexin was more effective. Each of the myotoxic enzymes substantially inhibited Ca(2+) uptake into sarcoplasmic reticulum, notexin being the most effective in this regard. This ability correlated better with their myotoxic potency than with their phospholipase A(2) activity. beta-Bungarotoxin lost its toxicity but not its measurable phospholipase A(2) activity after modification with ethoxyformic anhydride in the presence of dihexanoylphosphatidylcholine. The modified toxin also lost most of its ability to inhibit Ca(2+) uptake into sarcoplasmic reticulum and brain mitochondria. Sarcoplasmic reticulum vesicles reconstituted from solubilized sarcoplasmic reticulum retained their sensitivity to notexin.

Animals↗