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N G Christensen

Publications and source records attributed to N G Christensen.

14 recordsLinked to original sources
PubMed2006

External quality assessment of prothrombin time: the split-sample model compared with external quality assessment with commercial control material.

OBJECTIVE: CoaguChek S is a point-of-care, whole-blood, prothrombin time monitor. The purpose of this study was to compare two different methods for external quality assessments of CoaguChek S. MATERIAL AND METHODS: In the traditional external quality assessment scheme, commercial control material was sent to office laboratories and the results were compared with a method-specific target value. In the alternative external quality assessment (the split-sample survey) patient samples were analyzed on CoaguChek S at office laboratories, and venous blood samples from the same patients were analyzed at a hospital laboratory using an assigned comparison method. To obtain comparable performance criteria for the two methods, the limits for "good", "acceptable" and "poor" performance evaluation in the split-sample survey had to be expanded because of uncertainties in preanalytical factors and the comparison method. RESULTS: In the traditional external quality assessment the total imprecision (between-office and within-office) was 8.0% at the low level (1.6 INR (International Normalized Ratio)) and 10.5% at the therapeutic level (3.4 INR). In the split-sample survey the total imprecision was 12.3% at the low level (2.1 INR) and 10.7 % at the high level (3.0 INR). Seventy-five percent of the participating office laboratories were characterized as "good" with the traditional external quality assessments, whereas the corresponding number was 73% using the split-sample model. CONCLUSIONS: Available commercial control material for CoaguChek S is different from patient samples. This study demonstrates that split-sample survey is achievable, and is an acceptable alternative to traditional external quality assessment for point-of-care prothrombin time monitors where appropriate control material is difficult to obtain.

International Normalized Ratio↗
PubMed2001

[Quality of rapid tests for determination of infectious mononucleosis].

BACKGROUND: The Norwegian centre for quality assurance in primary health care, NOKLUS, was established in 1992 to ensure the quality of laboratory analyses performed in primary health care. This article evaluates results from the surveys of infectious mononucleosis. MATERIAL AND METHODS: From 1996 to 2000, five serum panels were sent to participating practices in order to control test-kits designed for serological rapid diagnosis of infectious mononucleosis. 648 practices participated in this external quality assessment in 2000. Target values were determined using the Paul Bunell Davidsohn test. The results obtained for each type of test and variables that might have affected the results were evaluated. RESULTS: Outdated kits or kits close to the date of expiration showed poorer results than the other test-kits. The quality of the results depended mainly on the type of test-kit used and the training level of the persons performing the analyses. INTERPRETATION: The best performing tests in these surveys were Clearview IM (Unipath Limited) and Contrast Mono (Genzyme diagnostics). These two tests are among the three most frequently used tests, out of a total of thirteen, in our surveys.

Agglutination Tests↗
PubMed1998

[Better quality of thrombotest in family practice. Results from the NOKLUS survey 1993-97].

The Norwegian centre for external quality assurance of primary health care laboratories (Norwegian abbreviation: NOKLUS) was established in 1992. In 1997 about 1,800 practices participated in NOKLUS' quality assurance schemes, and 576 of these participated in the PT survey. Participation is voluntary and free of charge. The interlaboratory variation (CV%) was 17.7% in 1993 and 13.3% in 1997, and the percentage of results classified as "poor" has decreased from 7-8% in 1993 to 4% in 1997. These data indicate that participation in the scheme has led to a widespread improvement in laboratory performance. Norwegian primary health care practices now seem to analyse PT just as accurately as the Norwegian hospital laboratories. Logistic regression showed that the two most important factors for ensuring quality analysis were having a medical laboratory technician perform the PT analyses, and using an analyzer rather than a manual procedure.

Family Practice↗
PubMed1996

[Quality of hemoglobin and glucose analysis in general practice. Results from the NOKLUS (Norwegian Health Authority) surveys 1994].

In 1992 the Norwegian health authorities and the Norwegian Medical Association initiated a joint project to secure the quality of laboratory analyses performed in primary health care. Two coordinated activities were established: in each of the 19 Norwegian counties a medical laboratory adviser was engaged, linked to the central clinical chemistry laboratory in that county. These advisers assist general practitioners and primary care specialists in securing the quality of laboratory procedures performed on their own premises. In addition, a Norwegian centre for external quality assurance in primary care (Norwegian abbreviation NOKLUS) was established. In 1994 NOKLUS had about 1,600 participants (comprising 95% of the relevant general and specialist practices). Tolerated limits are based on target intervals combined with a percentage tolerated deviation. Fresh material is used for haemoglobin, and target values are determined by two independent laboratories using the reference method. The article describes the results of the surveys of glucose and haemoglobin tests in 1994.

Blood Glucose↗
PubMed1991

Performance of cell counters in primary health care.

The results are presented from two external quality control surveys of cell counters in primary health care. The precision of haemoglobin measurements in the normal range was better than that obtained by conventional haemometers. The analytical quality of leucocyte analyses was about the same as that performed by hospital instruments. The precision of cell counters with respect to thrombocytes was poorer than that obtained on hospital instruments, especially in the lower level. Celldyn and Sysmex instruments performed best among the instruments examined. Reliable cell counter results were associated with medical laboratory technicians as operators of the instruments. To improve the analytical quality of the laboratory in primary health care, it appears necessary to establish an external quality assurance programme, including a laboratory consultancy service.

Blood Cell Count↗
PubMed1989

[Glucose analysis in general practice. An examination of 4 instruments designed for general practice and self-monitoring].

Several examinations have shown that the analysis of glucose in primary health care is of poor quality. The reason could be the quality of the instruments and/or the way the instruments are operated. We have examined Glucometer II, Glucochek SC, Reflolux II and Hypocount GA. These instruments were studied both in general practice and at Haukeland Hospital. The test results were compared with the routine used in the hospital laboratory. There were no major analytical differences between the instruments. All the instruments were found to have an analytical quality lower than what is recommended by the Norwegian Quality Control. The requested analytical quality for the instrument depends on the clinical needs. We would recommend that these glucose instruments be used to diagnose acute hypo/hyperglucemia and to some extent in control of diabetes. For a certain diagnosis of diabetes, the use of a more precise instrument is to be preferred. The need for a Quality Control program for glucose measurement in primary health care is emphasized.

Blood Glucose↗
PubMed1989

Performance of dry-chemistry instruments in primary health care.

The results from an external quality control of dry-chemistry instruments are presented. The performance with regard to imprecision was good. With regard to accuracy, the performance was poor for aspartate aminotransferase, creatine kinase, lactate dehydrogenase, triglycerides and uric acid. The inaccuracy of alanine aminotransferase, bilirubin, cholesterol, creatinine, glucose and potassium was comparable to that obtained by hospital instruments using wet chemistry. There were no large differences with respect to quality between Seralyzer and Reflotron. However, Seralyzer users performed more analyses per week, analysed a higher number of constituents and had more experienced operators than the Reflotron users. Reflotron users more often analysed the sample in connection with the consultation. The importance of an established quality control programme for these instruments is underlined.

Blood Chemical Analysis↗
PubMed1989

Influence of lipid and leukocytes on the haemoglobin determination by Coulter Counter S Plus III, Technicon H 6000, Technicon H 1, LK 540, Reflotron and Hemocap.

The influence of lipid and high concentrations of leukocytes on the haemoglobin determination by six different instruments was examined. The increase in the determination of haemoglobin concentration with elevated amounts of lipid in the samples was greatest with the Coulter Counter S plus III and the Technicon H 1 followed by the LK 540 and the Technicon H 6000. There was no effect of lipid on the haemoglobin determination using the Reflotron. High concentrations of leukocytes increased the haemoglobin determination most by Coulter Counter S plus III and Hemocap. There were no changes in the haemoglobin determinations by the LK 540 and the Technicon H 6000 when the samples contained increased amounts of leukocytes.

Hemoglobinometry↗
PubMed1988

Evaluation of serum separator tubes as a mail transport device in primary health care.

Serum separator tubes were evaluated as a serum separator system and a mail transport device. Using conventional tubes as controls, 26 serum constituents were examined. The samples were mailed from three different general practitioners to a central laboratory. Thirteen constituents had concentrations that were significantly different from the concentration in the conventional tubes. When medically important coefficients of variations were taken into account, however, the changes of only two constituents (potassium and cobalamin) were regarded as important.

Blood Chemical Analysis↗
PubMed1979

Stool porphyrins determined by high pressure liquid chromatography and by fractional hydrochloric acid--ether extraction.

When stool copro- and protoporphyrin were quantitated by spectrophotometry, after fractional hydrochloric acid-ether extraction, up to 30% of the protoporphyrins were recovered in the coproporphyrin extract. In disorders with elevated stool protoporphyrin excretion (e.g. erythropoietic protoporphyria), this method therefore may give falsely elevated coproporphyrin values. When the stool porphyrins were determined by high pressure liquid chromatography there was no carry-over of protoporphyrin to coproporphyrin. The recoveries were 82 and 87%, and the coefficients of variation 5.6 and 3.1% for proto- and coproporphyrin, respectively. Moreover, in specimens containing a more complex mixture of porphyrins, a complete separation of the C2-C8 porphyrins and porphyrin isomers was obtained in a single run. High pressure liquid chromatography should therefore be considered the method of choice to obtain a quantitative profile of stool porphyrins in the routine laboratory.

Chemical Fractionation↗
PubMed1977

A rapid assay for urinary porphyrins by dual-wavelength spectrophotometry.

A procedure has been developed for the separation and quantitative assay of urinary porphyrins. Urine was directly diluted to a final concentration of 1 MHCl and the amount of porphyrins was determined from the peak-to-trough height deflection of the first derivatives of the absorption spectrum in the region of the Soret band. The ratio uro-/coproporphyrin was determined from the wavelength at which the spectrum intercepted the baseline. The specificity (as shown by a correlation coefficient of 0.99 compared to the method of Doss and Schmidt (1971) Z. Klin. Chem. Klin. Biochem. 9, 415-418), precision (coefficient of variation 5.2 percent) and sensitivity (lower detection limit approx. 0.01 mumol/l) of the present method were highly sufficient to estimate total and different porphyrins in the routine laboratory.

Coproporphyrins↗