Biomedical subjects

G Röhle

Publications and source records attributed to G Röhle.

At least 19 recordsLinked to original sources

PubMed1998

External quality assessment of molecular biology-based methods used in laboratories of clinical chemistry and human genetics.

The Reference Institute of Bioanalysis of the German Society of Clinical Chemistry has performed the first external assessment of molecular genetics methods used in medical diagnosis. The following procedures were tested: (I) DNA preparation from whole blood, (II) PCR amplification using "standard" primers, and (III) submarine agarose gel electrophoresis. Out of 50 participants, 45 returned samples for evaluation.

Chemistry, Clinical↗

PubMed1994

Concentration-dependent profiles for describing the scatter of results of interlaboratory surveys.

In an interlaboratory survey for the quantitative determination of a clinical chemical quantity, samples of the same specimen are analysed in different laboratories. If the number of participating laboratories is sufficiently large, then the differences between the 50th percentile (median) and e. g. the 25th and 75th percentiles of the results give a very reliable impression of the range of interlaboratory scatter for the particular analytical technique. Results from a relatively large number of interlaboratory surveys, in which specimens containing different concentrations of the analyte are investigated, can be handled in the same way. If the resulting differences between the chosen percentiles are plotted against the median, and the corresponding two regression lines (upper and lower) are drawn, the results are asymmetric scatter profiles covering the concentration range of the specimen collective. Numerous options are available. Thus, a profile's power of characterizing the scatter correctly can be improved by weighing of the results. Moreover, scatter profiles can be based on different variables of the survey, such as the analytical method, or the observation period, etc. They may be based on the total collective of all results for a given quantity, or they can be constructed for subcollectives of results obtained with a single analytical method. Further, it is possible to present the results of all subcollectives in a single pair of scatter profiles. This latter type of analysis provides profiles of the average scatter for a collective of different analytical methods, which are unaffected by any systematic differences that may exist between the methods.

Blood Chemical Analysis↗

PubMed1993

Interlaboratory surveys of the determination of tumour markers scatter and repeatability of the results.

Data collected between 1983 and 1991 in interlaboratory surveys of the determination of tumour markers are used to show the magnitude of the scatter of results from different laboratories for the analysis of a single quantity in a given matrix. These data also show that the varying specificity of different reagent combinations appears to make a considerable contribution to this scatter, and that the used reagent combinations were not of uniform quality over a relatively extended period. The results for the following tumour markers were studied: alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), human chorionic gonadotropin (hCG), human chorionic gonadotropin+beta-subunit (hCG+beta-hCG), tissue polypeptide antigen (TPA), carbohydrate antigen 19-9 (CA 19-9), cancer antigen 15-3 (CA 15-3), cancer antigen 125 (CA 125), prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA).

Acid Phosphatase↗

PubMed1993

Calibrators and control samples for bilirubinometers.

The different matrix properties of neonatal serum and commercial control samples can lead to considerable errors in the calibration and control of bilirubinometers. These difficulties can be avoided by calibration with serum from healthy adults which is supplemented with unconjugated bilirubin. But this procedure is impracticable for most routine laboratories. Under certain preconditions, control samples, with bilirubin concentrations determined with correctly calibrated bilirubinometers or spectrophotometers, are also suitable as calibrators. This was established by determination of the bilirubin concentration of 16 different control samples, using both the reference method and correctly calibrated bilirubinometers or spectrophotometers in three or four specialist laboratories. This was also confirmed in several interlaboratory surveys, some involving up to 72 laboratories. The results of these investigations show that a control sample should be used for the calibration of a bilirubinometer only if it meets the following preconditions: 1. There should be no significant difference between the bilirubin values determined with the reference method and with a correctly calibrated spectrophotometer or bilirubinometer. 2. The bilirubin concentration should lie in the range 230-300 mumol/l. The photometric response of bilirubinometers has a limited linear range, so that analytical results greater than 300 mumol/l must be rated as basically unreliable.

Bilirubin↗

PubMed1991

Our experience with quality control in current growth hormone assays.

For many years now the German Society for Clinical Chemistry has organized interlaboratory surveys by order of the Federal Medical Association. Human growth hormone (GH) is one of 20 endocrine parameters included in a set of two control specimens and offered to survey participants at least 4 times a year. Since no reference method exists for GH, the 'true value' remains unknown. Thus, evaluating survey results is limited to a presentation of how far one participant's results agree with those of other participants using the same or different methods. Medians and percentiles are calculated for all participants and, when possible, for subgroups using the same kit. Over the last years, 60-80 laboratories have participated in each GH survey with 12-16 different kits. The participants' results have shown considerable scatter with differences in GH levels of several hundred percent. The largest discrepancies have occurred with specimens of low GH concentrations, those especially interesting for pediatricians. An evaluation of subgroups using the same kit has shown a relatively good group agreement but large method-dependent differences between these groups. As regards the median, the results of different kits varied by as much as 250%. Accordingly, different reference values have to be applied to different GH kits. For the last 3 years not only have several companies changed their methods, but also one third of the laboratories participating in the survey have switched to other GH kits. This leads us to wonder if all the clinicians served by these laboratories are being informed of this and of any resulting discrepancies in their GH parameters.

Chemistry, Clinical↗

PubMed1990

Comparison of five routine methods with the candidate reference method for the determination of bilirubin in neonatal serum.

Using five routine methods and the candidate reference method of Doumas (Clin. Chem. 31, 1779-1789 (1985)), total bilirubin was determined in 77 neonatal serum samples (concentration range 63-444 mumol/l, average value 227 mumol/l). Four of the routine methods (Jendrassik & Grof's (Biochem. Z. 297, 81-89 (1938)) method, Hertz's (Scand. J. Clin. Lab. Invest. 33, 215-230 (1974)) method, the bilirubinometer procedure, and the method employing 2,5-dichlorophenyldiazonium (Scand. J. Clin. Lab. Invest. 29, Suppl. 126, Abstr. 11. 12. (1972]) gave values that were generally higher than those of the reference method. In contrast, the results from Vink's (Clin. Chem. 34, 67-70 (1988] direct spectrophotometric method differed only negligibly from those of the reference method. The accuracy of Jendrassik & Grof's method, and to a limited extent that of the 2,5-dichlorophenyldiazonium method, can be improved by redetermination of the molar absorption coefficient, or by using a standard containing a matrix of human albumin, with an assigned value determined by the reference method. It was found that Hertz's direct spectrophotometric method can be replaced by that of Vink. The accuracy of the bilirubinometer results could be improved only by using calibrators with assigned values specific for the bilimeter, or by calibration with a serum pool.

Bilirubin↗

PubMed1989

External quality assessment of absorbance measurements on spectral and spectral-line photometers.

From 1984-1987, 12 quality control surveys on photometric measurements were carried out in 600-800 laboratories. The participants measured the photometric absorbance of the control samples at 4 wavelengths of the mercury spectrum: 334.1 nm, 365.4 nm, 404.7 nm and 546.1 nm. The medians of the results were without exception lower than the target values, but only very few of them deviated more than 1%. The dispersion of the values did not follow a normal distribution. Two thirds of the values were concentrated within a very small range, while about 10% lay outside the 2- to 3-fold range. It was found that longer wavelengths resulted in a smaller dispersion of readings than shorter ones. Furthermore, precision showed a significant dependency on the absorbance readings of the samples, on the one hand, and on the different photometers, on the other.

Chemistry, Clinical↗

PubMed1988

External quality control in the determination of neonatal bilirubin. An approach to the improvement of results.

The reliability of bilirubin analyses is especially important in cases of neonatal hyperbilirubinaemia. However, when the means of the results of external quality control surveys and the method-dependent stated values for control sera were compared with reference method values, differences of up to 10% were found. Further inaccuracy arose from interlaboratory imprecision, which showed coefficients of variation of at least 7%, and from greater or lesser interference from contamination of samples with haemoglobin. The present work investigates whether the current situation can be improved by available means.

Bilirubin↗

PubMed1987

Report on a joint European quality control survey for neonatal thyrotropin determinations (1986).

This paper presents the results of a joint European external quality control survey for thyrotropin determinations in blood dried on filter paper, carried out in 1986 in cooperation with several national quality control organizations. For the evaluation, 124 participants presented their individual diagnostic classifications in addition to their analytical results. Although, in relation to earlier studies of this kind, there was a significant improvement in interlaboratory precision the results still showed variance which depended on the analytical method and, possibly on the country in which it was performed. Regional differences were also evident in the diagnostic classifications.

Europe↗

PubMed1983

Results of quality control surveys of radioimmunological determinations of thyrotropin in newborns.

Within the quality control scheme of the Deutsche Gesellschaft für Klinische Chemie, seven quality control surveys of thyrotropin (TSH) determinations in blood dried on filter paper have been carried out since 1980. Ninety-six screening laboratories from 12 European countries took part in these surveys. In a single survey each participant usually analysed four different samples; each of these consisted of three spots of dried blood spiked with defined amounts of thyrotropin. For the evaluations of the surveys the participants were asked to give information about their analytical results, and from these, their diagnostic classifications. The medians of the analytical results correlated well with the given thyrotropin concentrations, but the individual estimations from different laboratories varied greatly. Major discrepancies of classification were also apparent, both in the given thyrotropin concentrations and in the individual estimations. Two special collaborative studies with nine selected laboratories showed on the one hand that analysis of the largest possible part of the dried blood sample can help to optimize the precision of the results; on the other hand, considerable drawbacks related to the reagents and the methods were sometimes observed.

Blood Specimen Collection↗

PubMed1983

[Collaborative tests of steroid hormone determinations: accuracy and precision of analytic results].

In the years 1977 to 1981, 14 quality-control surveys for the determination of steroid hormones were performed in cooperation with the Deutsche Gesellschaft für Klinische Chemie. Hereby the laboratories participating could in each case analyze the following steroids: aldosterone, cortisol, oestradiol-17 beta, oestriol, progesterone, and testosterone. In the light of the results an investigation was made as to whether, in the course of time, an improvement in the accuracy or in the precision of the determinations had been attained, and to what extent the determinations depend on the qualities of the test material. A clear improvement in the accuracy of the results of the analyses could only be ascertained for oestradiol-17 beta. For aldosterone and cortisol, values were found in pool-plasma whose medians were significantly above the definitive values. An improvement in precision could be noted especially with oestradiol-17 beta and to lesser degrees with cortisol and oestriol. The kind of test material--plasma which contained only the hormones to be analyzed on the one hand, and, on the other hand, pool-plasma, which also contained all endogenous hormones--had no influence on the precision of the results from various laboratories. Low concentrations of the individual steroids led--on the basis of the methodological principle of radioimmunoassays--in almost all cases to a reduced interlaboratory precision in regard to values. The accuracy of the analysis values was considerably impaired only with aldosterone and oestradiol-17 beta by low concentrations: the medians here were in part twice as high as the definitive values.

Aldosterone↗

PubMed1982

[Results of quality control surveys for urinary calculus analyses].

In 1980 and 1981, four quality control surveys for urinary calculus analyses were carried out, within the framework of external quality controls of the Deutsche Gesellschaft für Klinische Chemie. During these quality control surveys the participating laboratories received a total of 16 samples (eight pure substances and eight mixtures of two components), to be analyzed qualitatively and quantitatively. For the qualitative analyses, a laboratory could provide simplified descriptions of the analytes - for example, without stating the number of molecules of the water of crystallization; or, to the extent permitted by the mode of analysis, the exact chemical composition could be presented. Of 1283 analyses, 818 (64%) attained the goals of the simplified analysis. The most frequent errors in chemical analyses were false negative and false positive results for calcium oxalate, and false negative results for calcium phosphate. Laboratories using analysis by infrared spectroscopy also submitted the biggest proportion of incorrect analyses for these components. The most reliable results were produced by X-ray-diffraction: 86% of the results in this category represented correct differentiated analyses. The generally accurate results achieved by some participants using chemical analysis suggest, however, that - in addition to the principle of analysis used - the qualification of the operator is an important determinant in the reliability of the results.

Calcium Oxalate↗

PubMed1981