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Biomedical subjects

A P Jansen

Publications and source records attributed to A P Jansen.

At least 19 recordsLinked to original sources
PubMed1990

Spinal angiomas. The meaning of cerebrospinal fluid lactic acid in the etiology and differential diagnosis of transverse myelopathy.

We report five out of eleven patients with transverse myelopathy due to spinal angiomas. Transverse myelopathy can be caused by a number of disorders. The formation of lactic acid points to ischaemia within the spinal cord, due to altered haemodynamics as in spinal angiomas. The meaning of cerebrospinal fluid lactic acid is discussed with respect to etiology and differential diagnosis of transverse myelopathy. The combined finding of CSF lactic acid and protein elevation in the absence of cell count and immunological and/or serological abnormalities points to an isolated vascular cause of the transverse myelopathy.

Adolescent↗
PubMed1988

Modification in Ramsay's method for correct measurement of total iron-binding capacity.

Lack of satisfactory literature evidence and experiences with results of quality control assessment trials in The Netherlands prompted reconsideration of the determination of total iron-binding capacity (TIBC) in human and control sera. It was found that for a correct determination of serum TIBC the Fe(III)-saturating reagent must be able to correct an abnormally high serum pH due to a subnormal CO2 content of the sample. Such low CO2 contents are frequently found in reconstituted quality control sera. Detailed studies on combinations of mixtures of serum with varying pH and Fe(III)-saturating solutions with increasing amounts of added acid revealed a linear equation of the minimum amount of acid needed in relation to the original serum pH.

Carbon Dioxide↗
PubMed1986

Simultaneous spectrophotometric calibration of wavelength and absorbance in an interlaboratory survey using holmium oxide (Ho2O3) in perchloric acid as reference, compared with p-nitrophenol and cobaltous sulphate solutions (1978-1984).

The wavelength accuracy of ten different types of spectrophotometer was tested with holmium perchlorate solutions. It was found to be good, with mean deviations from the literature values of maximally 0.3 nm. Standard deviations over the entire spectral range were within 0.75 nm. The absorbance accuracy for different types of instruments was generally within 5%, except in the 287 nm range where higher deviations were found. The sharpness of the holmium peaks, in combination with band width and sensitivity of the instruments, troubled the majority of the participants. 150 spectrophotometers were involved in the surveys. Linearity of the spectrophotometers was tested with p-nitrophenol and cobaltous sulphate and found to be satisfactory.

Chemical Phenomena↗
PubMed1986

Minimizing interlaboratory variation in routine assays of serum cholesterol through the use of serum calibrators.

A cholesterol standardization program was developed in The Netherlands for clinical laboratories that use their analytical results as indicators of cardiovascular risk. Participants with sufficient precision but inaccurate results are encouraged to use serum-based calibrators as a means to decrease bias. A regional pilot survey and thereafter a national one were carried out in 31 and 138 laboratories, respectively, to investigate whether use of the serum-calibration procedure could improve routinely performed cholesterol measurements. To participants in our national quality-control surveys were mailed three calibrators (pooled human serum) and five human-serum controls, for analysis of cholesterol on four different days. Reference method values had been assigned to the calibrators by the Netherlands Reference Laboratory, applying the U.S. Centers for Disease Control modification of the Abell-Kendall procedure. Using the calibration curves based on results for the serum calibrators decreased the between-laboratory variation (SD) by at least 50%, with improved accuracy for non-enzymatic methods. The initial within-laboratory precision was generally good, and improvements in it were small. To our knowledge, standardization results involving so many routine hospital laboratory procedures have not been previously reported.

Calibration↗
PubMed1984

Five methods for determining low-density lipoprotein cholesterol compared.

We evaluated three precipitation methods for determination of low-density lipoprotein cholesterol in serum and an indirect method involving the Friedewald formula (Clin Chem 18: 499-502, 1972) by comparison with results by ultracentrifugation. The results of all methods for 83 sera, including 59 hyperlipidemic type IIA, IIB, and IV sera agreed very well, at least for concentrations of serum triglycerides below 8 mmol/L. The accuracy of the Friedewald formula was confirmed in 285 other sera, including 66 sera with triglycerides content between 4.52 and 8.0 mmol/L. For type III sera, the precipitation methods produced similar values to those obtained with the Friedewald formula, all being much higher than the ultracentrifugation values. Density-gradient ultracentrifugation showed that the very-low-density lipoprotein remnants in type III sera almost completely coprecipitated with the low-density lipoproteins. The precipitation methods are not only accurate but also very precise (CV less than 5%); they can therefore be used in clinical laboratories to measure atherogenic low-density lipoproteins plus the remnants of very-low-density lipoproteins. However, when serum triglycerides and high-density lipoprotein cholesterol also are determined, the Friedewald formula is a reliable alternative.

Centrifugation, Density Gradient↗
PubMed1984

Suitability of various control sera for use in testing the accuracy of cholesterol determination with enzymic kits.

We used 20 different commercial enzymic kits to measure cholesterol in 19 commercial control sera and in a pooled specimen of human serum and compared the relative biases, with the Abell -Kendall procedure as reference. Our purpose was to select those sera in various enzymic kits showing behavior similar to that of human serum and which thus can be used to measure the accuracy of these kits. The overall mean relative biases obtained with each of the 20 kits for the pooled human serum on the one hand and for a given control serum on the other generally correlated significantly. On the basis of the correlation coefficients and regression equations, we could select the control sera best suited for measurement of accuracy. They were all human-serum based, with cholesterol concentrations greater than 5 mmol/L. Animal sera with above-normal lipid values produced by feeding special diets appeared to be less reliable control sera in this respect.

Animals↗
PubMed1983

Standards versus standardised methods in enzyme assay.

In a trial of the Netherlands coupled external/internal quality control program a control serum and an enzyme standard were analysed over a period of eight weeks, five times each week. Five enzymes were determined: alkaline phosphatase, creatine kinase, lactate dehydrogenase, alanine aminotransferase, and gamma-glutamyltransferase. The measured values in the serum were converted to the standards. Those laboratories using the recommended methods also submitted their non-transformed serum values. The following standardisation techniques have been compared: (a) no standardisation of methodology but use of enzyme standards; (b) standardisation of methodology; (c) standardisation of methodology combined with use of an enzyme standard. Results were submitted to analysis of variance. Standardisation of methodology did not yield smaller interlaboratory variation than the standardisation with enzyme standards. In this trial a combination of both standardisation techniques yielded generally better results. Results for gamma-glutamyltransferase indicate that standardisation of substrate may be necessary apart from the use of an enzyme standard. The preparation of stable enzyme standards is stressed.

Alanine Transaminase↗
PubMed1983

Evaluation of accuracy of 20 different test kits for the enzymic determination of cholesterol.

We evaluated the accuracy of 20 different test kits for the enzymic determination of cholesterol. Using a selected set of standards, we found mean values differing by -9.9 to + 10.7% from values obtained by the Abell-Kendall procedure. Nine kits gave values with a relative bias of less than 2.5%. In the case of the other 11 kits, recalculation with secondary serum standards resulted in values within 5% of the reference values. Depending on the kit used, two different commercially available standard solutions produced results differing by, at most, 8.7%. We obtained indirect evidence that use of esterase of bacterial origin is associated with low values. We ascribe the high values obtained with some kits to positive interference by stabilizers or unspecified compounds in the reagents.

Cholesterol↗
PubMed1982

Stability of frozen liquid control sera for assay of cholesterol in high-density lipoprotein.

Liquid serum pools with low-, normal-, or above-normal concentration of high-density lipoprotein cholesterol were prepared by selection and dilution of sera having low lipoprotein content or by enrichment with concentrated high-density lipoprotein. Stability of the serum pools depended on storage conditions. On storage between -2 and -12 degrees C, the high-density lipoprotein cholesterol content decreased. At a constant temperature of -19 to -21 degrees C the concentrations remained stable for more than 18 months. The imprecision (CV) of the high-density lipoprotein cholesterol assay during this period as established with enzymic cholesterol analysis (Clin. Chem. 26: 1780-1786, 1980) of these serum pools was between 2.7 and 4.8% (n = 51). Serum pools prepared and stored as described are suitable for internal quality-control procedures. In external quality-control trials these sera may be superior to the commercially available lyophilized lipid control sera.

Blood Preservation↗
PubMed1982

Enzymic and chemical-extraction determinations of free fatty acids in serum compared.

We compared an enzymic test kit for determination of free fatty acids in serum (NEFA C-test, WAKO) with two modifications of a chemical extraction procedure, I (Clin. Chim. Acta 43: 317-320, 1973) and II (Clin. Chim. Acta 80: 327-332, 1977). All three procedures are specific for long- and medium-chain fatty acids. Short-chain fatty acids, some keto acids, and phospholipids did not interfere. Added fatty acid was quantitatively accounted for in all methods. Results obtained with the enzymic method and II did not differ significantly, whereas the results by I were about 10% lower. The concentration of NaCl in the copper reagent, but not the kind of solvent used to dissolve the standard, influenced the accuracy of the chemical methods. In the enzymic procedure, hydrolysis of triglycerides during incubation is unlikely to be the reason for too-high values. The precision of all three procedures is acceptable for use in clinical laboratories.

Fatty Acids, Nonesterified↗
PubMed1980

A study of the use of polyethylene glycol in estimating cholesterol in high-density lipoprotein.

We studied polyethylene glycol 6000 precipitation of lipoproteins other than high-density lipoproteins, before cholesterol is estimated in the supernate. Other lipoproteins in the supernatant fractions were detected by using rocket immunoelectrophoresis. A polyethylene glycol concentration of 75 g/L in the final mixture appeared to be optimal, and results agreed with those obtained by ultracentrifugation. Differences in serum pH, use of polyethylene glycol from different suppliers, or the presence of ethylenediaminetetraacetate resulted in values that differed significantly (by 40 to 60 mumol/L) from the reference values. Polyethylene glycol did not interfere in four different methods for determination of cholesterol. In combination with an enzymic cholesterol method, the polyethylene glycol method appeared to be very precise, even when lipemic sera (triglycerides up to 5.5 mmol/L) were analyzed that had diminished high-density lipoprotein cholesterol values. We consider this method a method of choice, especially when lipemic sera are tested and enzymic cholesterol analysis is used.

Cholesterol↗