PubMed Health⌕ Search

Biomedical subjects

M Knedel

Publications and source records attributed to M Knedel.

At least 19 recordsLinked to original sources
PubMed1990

Demonstration of a combined deficiency of xanthine oxidase and aldehyde oxidase in xanthinuric patients not forming oxipurinol.

Genetic heterogeneity has been suggested in xanthinuria from the hitherto unexplained ability of some patients with this hereditary disorder to convert allopurinol to its active metabolite oxipurinol--an activity generally attributed to xanthine oxidase. This study provides evidence that the enzyme aldehyde oxidase is also deficient in xanthinuric patients not converting allopurinol to oxipurinol, whereas a xanthinuric patient with normal formation of oxipurinol had normal aldehyde oxidase activity. It is concluded that the enzyme aldehyde oxidase is the principal enzyme responsible for the formation of oxipurinol in man.

Adult↗
PubMed1990

Multicentre evaluation of the Boehringer Mannheim/Hitachi 717 analysis system.

We conducted an European multicentre trial to assess the performance of the new Boehringer Mannheim/Hitachi 717 analysis system. The photometer response was linear up to an absorbance of 2.8. The maximal CV of photometric imprecision was 0.5% for the wavelength pair 340/405 nm within the absorbance range 0.9 to 2.4. For the 13 analytes in our study, mean within-run imprecision was less than 2%, and mean between-day imprecision less than 2.5%. The results obtained with the Hitachi 717 instrument correlated closely with those of comparison instruments. Linearity for the various tests was high and exceeded the manufacturer's claims. No drift was detected during an 8-hour work period; carry over could not be detected under the chosen experimental conditions. The new instrument was readily accepted by the evaluators because of its ease of handling and simple daily maintenance.

Blood Chemical Analysis↗
PubMed1989

Isocratic ion-pair high-performance liquid chromatographic methods for the determination of uroporphyrin and coproporphyrin type II and IV isomers in human urine.

Urinary porphyrins of porphyric patients were isolated as their methyl esters by using a simple, modified thin-layer chromatographic system. Existing methods for the isocratic ion-pair high-performance liquid chromatographic separation of uroporphyrin and coproporphyrin isomers were decisively improved by elevating the column temperatures, changing the types of columns used and modifying the eluent compositions. These techniques were applied to the determination of the isomeric distribution of uroporphyrins and coproporphyrins isolated from urines of patients in the acute or latent phase of acute intermittent porphyria. In these urines relatively high contents of the atypical uroporphyrins II (2-5%) and IV (13-19%) were found. The coproporphyrin fractions contained significantly smaller amounts of the atypical isomers II (1-2%) and IV (2-5%), the presence of which was demonstrated for the first time in such urines. Several mechanisms for the formation of the atypical coproporphyrin isomers are discussed. The isocratic ion-pair separation method served also to control the isomeric purity of uroporphyrin specimens of both natural and synthetic origin.

Chromatography, High Pressure Liquid↗
PubMed1988

Evaluation of a new chemiluminescence immunoassay for the determination of human chorionic gonadotropin in serum.

A new commercially available chemiluminescence immunoassay for the quantitative measurement of human chorionic gonadotropin and its beta-subunit in serum was compared with the enzyme immunoassay used in our routine laboratory. Human chorionic gonadotropin was determined in serum from pregnant women, as well as from women with abortus imminens, suspected ectopic pregnancies or with molar pregnancies. The new human chorionic gonadotropin assay was also evaluated in combination with an automatic sample processor for distributing samples to the antibody-coated wells of the microtitre plates. The analytical precision, specificity and accuracy of the human chorionic gonadotropin assay were assessed with 152 sera, using the 60 min-incubation as well as the shorter 15 min version. Specificity was comparable with the conventional system, whereas the chemiluminescence assay performed better with respect to the assay detection limit and measuring range. The enhanced chemiluminescence system for the determination of human chorionic gonadotropin is an efficient assay which agrees well with our routine assay. In connection with an automatic sample processor it enables an advanced and versatile system for the determination of human chorionic gonadotropin in laboratories with large series. The system is rapid, easy to handle and apparently free from interference.

Choriocarcinoma↗
PubMed1979

[Determination of thyroxine in serum by a heterogeneous enzyme immunoassay: results of a joint trial].

This paper describes the evaluation of a heterologous enzyme immunoassay for the determination of total thyroxine in serum by a group of seven clinical chemical laboratories. The test follows the principles of the enzyme linked immunosorbent assay (ELISA) and uses peroxidase as a marker. The evaluation of analytical reliability yielded the following results within the analytical range from 39 unto 322 nmol/l: 1. Within-batch precision ranged from 3.1 unto 10.4% (coefficient of variation) with single analyses. 2. Between-batch precision ranged from 3.7 unto 20.4% with single analyses. 3. Between-laboratories precision ranged from 5.4 unto 6.8%. 4. Pure thyroxine, added to serum or thyroxine-free serum, gave recoveries between 93 and 120%. 5. Analysis of control sera gave results essentially comparable to the assigned values based upon radioimmunoassays. 6. Analysis of 288 clinical sera gave slightly higher results by the enzyme immunoassay than by the analogous radioimmunoassay from the same manufacturer. 7. Comparison with other methods of analysis (radioimmunoassays, competitive protein ligand assays, hormonal iodine assay) yielded partly comparable, partly higher results. 8. Comparison with the homogenous enzyme immunoassay (EMIT) led to comparable results. 9. Interference due to hyperlipemia or hemolysis was not observed. 10. There might be an interference in hyperbilirubinaemic sera, due to an as yet unknown factor. With respect to practicability the ELISA-test compares favourably with the analogous solid phase radioimmunoassay. The main differences are the absence of radioactive material and a longer shelf-live of reagents. Following the manual procedure the time taken to perform the enzyme immunoassay is slightly longer than for the analogous radioimmunoassay.

Enzyme-Linked Immunosorbent Assay↗
PubMed1978

Quantitation of adrenaline and noradrenaline from human plasma by combined gas chromatography--high-resolution mass fragmentography.

A gas chromatographic--high-resolution mass fragmentographic method for the simultaneous determination of adrenaline and noradrenaline from human plasma is presented. The catecholamines are separted by adsorption on alumina and converted by a selective, two-step procedure to the corresponding N-trifluoroacetyl-N-trimethylsilyl derivatives. The benzylic fragment C16H31O3Si3 (m/e 355.1568) of these derivatives is detected at a mass spectrometric resolving power of 5000. This high resolution detection was necessary to differentiate this fragment from others with the same nominal mass of 355 originating from the biological matrix and/or the bleeding from column and septum.

Epinephrine↗
PubMed1978

[Creatine kinase isoenzymes: idiopathic occurrence of creatine kinase BB activities in patient serum (author's transl)].

By differentiation of creatine kinase isoenzyme activities in sera using immunological methods the published data about occurrence of creatine kinase BB activities in patients with different diseases or after surgical treatment, respectively, cannot be verified in general. With a frequency in the order of magnitude of 1 : 1000 in the serum of old patients (age 57 to 85 years with one exception), however, creatine kinase BB activities can be measured. The range of activities is 15 to 234 U/1, or 19 to 94% of total creatine kinase activities, respectively. At the present time there is no possibility to correlate this phenomenon to any specific disease. These cases are detected by abnormally high results of CK-MB activity measurements with the immunoinhibition test (range 60 to 202% of total creatine kinase activities) which lead to a repeated analysis using immunoprecipitation. The results of all CK-BB patients investigated till now are presented and discussed.

Adult↗
PubMed1978

Performance of various mathematical methods for computer-aided processing of radioimmunoassay results.

Interpolation and regression methods are available for computer aided determination of radioimmunological end results. We compared the performance of 6 algorithms (weighted and unweighted linear logit log regression; quadratic logit log regression, smoothing spline interpolation with a large and small smoothing factor, respectively, and polygonal interpolation and the manual curve fitting on the basis of three radioimmunoassays with different reference curve characteristics (digoxin, estriol, human chorionic somatomammotrophin (HCS)). Great store was set by the accuracy of the approximation at the intermediate points on the curve, i.e. those points that lie midway between two standard concentrations. These concentrations were obtained by weighing and inserted as unknown samples. In the case of digoxin and estriol the polygonal interpolation provided the best results, while the weighted logit log regression proved superior in the case of HCS.

Computers↗
PubMed1978

[Isoenzymes of creatine kinase: distribution in the skeletal muscle and in sera of patients with muscular diseases or damages (author's transl)].

In skeletal muscle isoenzymes of CK were determined by immunprecipitation and chromatography. The activity of CK-MB was between 17 and 47 U/g muscle, corresponding to a quota between 2,1 and 4,2% of the total activity. In sera of patients with muscular dystrophy, polymyositis, hypothyroidism, after arterial embolism, epilepsy, hyperventilation, operations and polytrauma with and without injury to the thorax isoenzymes were measure by immune precipitation- and immune inhibition-test. The percentage of CK-MB in all sera was less than 6% of the total CK-activity (range: 0 to 6%). Only patients in the first day after neurosurgical operations showed a quota till to 6.5% CK-MB. In serum of patients after polytrauma without injury to the thorax the percentage of CK-MB ranged from 0-5.7% while after polytrauma with injury to the thorax and a reasonable suspicion of a damage to the myocardium this quota was between 5.1 and 23.6% of the total activity. CK-BB activity was not detectable in any cases. Therefore a disease or damage of the skeletal muscle is more probable, if the percentage of CK-MB in less than 6%, because in sera of patients with myocardial infarction in the first 48 h after beginning of the symptoms this quota of CK-MB in the most cases in more than 6%.

Creatine Kinase↗
PubMed1978

[Studies of activity kinetic of isoenzyme CK-MB in serum after myocardial infarction (author's transl)].

We investigated the activity kinetics of CK-total and CK-MB in 83 patients with proven myocardial infarctions. Serial serum samples were taken at intervals of 2--6 h. The activity of isoenzym CK-MB was determined by means of the immunological inhibition method. CK-MB activity was determined in all patients. The mean peak activity of CK-MB was 65 U/l (range: 9-241 U/l). At the time of peak CK-MB activity the mean percentage CK-MB activity was 13.2% (range: 3.4--21.7%). The CK-MB activity reached its peak at 17.4 h (range: 3.0--32.5 h) after the onset of retrosternal pain. This is 1.4 h after peak CK-total activity. The mean disappearance rate constant for CK-MB (n = 31) was found to be 9.3 X 10(-4) U/min with a large individual variation. This value corresponds to a half life of 12.5 h (CK-total: 15.5 h). The determination of CK-MB activity is therefore only of diagnostic significance within 48 h of possible myocardial occurrence. Moreover, isoenzyme CK-MB is not found exclusively in myocardium. For this reason it is better to use the percentage CK-MB activity in the differential diagnosis of myocardial infarction. With 80% of the patients this value is greater than 6% within 36 h of proven myocardial infarction.

Circadian Rhythm↗
PubMed1978

Mass spectrometry of dimethylthiophosphinates of aromatic hydroxy compounds.

The mass spectra of 20 differently substituted dimethylthiophosphinic esters of aromatic hydroxy compounds are presented. Fragmentation routes were investigated using high resolution mass measurements, decoupled metastable determinations and deuterium labelling. All compounds exhibited abundant molecular ions and typical phosphorus-containing ions. Characteristic elimination processes strongly dependent upon the respective type of substitution were observed. Due to their high stability, their great ease of formation and their good gas chromatographic properties these new types of derivatives are of special interest for establishing gas chromatography mass spectrometry profiles of acidic catecholamine metabolites.

Gas Chromatography-Mass Spectrometry↗
PubMed1977

Quantitative determination of creatine kinase isoenzyme catalytic concentrations in serum using immunological methods.

For the determination of creatine kinase isoenzyme catalytic concentrations in serum two methods based on immunological reactions are presented: One method uses inhibiting antibodies, which selectively block the activity of creatine kinase M subunits ("Inhibition Test"). This test is used for routine measurements of creatine kinase MB catalytic concentration; Another method uses precipitating antibodies, which allows a quantitative differentiation of creatine kinase isoenzymes MM, MB and BB ("Precipitation Test"). This test is used as a control for the Inhibition Test for the possible presence of creatine kinase BB activities in doubtful cases. Procedures, specificity, correlation and application of these methods are discussed.

Creatine Kinase↗