[Method selected for the determination of creatinine in plasma or serum. Choice of optimal conditions of measurement]. / Technique sélectionnée pour le dosage de la créatinine dans le plasma ou le sérum, Choix des conditions optimales de mesure.

The method selected by the SFBC (Société française de biologie clinique) is derived from the colorimetric reaction of creatinine with alkaline picrate, measured kinetically, without any pretreatment step. The key parameters of the reaction determining the quality of the results are studied, with special regard to samples including known interferents. The aims of the study were to gain an optimal analytical sensitivity and to reduce main interferences (acetoacetate, bilirubine, glucose, protein) which plague the Jaffé reaction, through a comprehensive study of the reagents, of their concentrations and of the analytical procedures. The selected concentrations (in the test) are: 150 mmol/L sodium hydroxide, 10 mmol/L picric acid and 2 g/L sodium dodecyl sulfate. Ten millilitres of a BRIJ solution (30% volvol) are added to the reagent. The operating procedures are as follow: sample ratio 0.07 to 0.08; wavelength 505 to 510 nm; temperature 37 degrees C; incubation of the specimen with the alkaline reagent 5 mn (at least), before starting the reaction with picric acid. A seric calibrator is recommended. The first measurement is taken 20 to 40 s after starting the reaction. Total measurement time is 120 to 150 seconds.

[Validation and study of the transferability of the selected technique by SFBC for the determination of creatinine in plasma]. / Validation et étude de la transférabilité de la technique sélectionnée par la SFBC pour le dosage de la créatinine dans le plasma.

A selected method for the determination of creatinine in plasma, using the reaction with alkaline picrate without prior pretreatment has been proposed by the Commission 'Validation de techniques' in the SFBC (Société Française de biologie clinique). The transferability step was conducted in seven laboratories, equipped with different automatic analyzers, using analytical procedures derived from the recommended method. Its goal was to test whether the original analytical performances could be maintained and consistent results obtained. The validation step was designed to evaluate the linearity limits of the analytical range, the detection limit, to assess accuracy as compared to a high performance liquid chromatography and to investigate the effect of the main interferents. Linearity limits are 15 and 2000 mumol/L. The detection limit is 3 to 8 mumol/L according to the analytical systems. The selected method can fulfil the set imprecision goals: intralaboratory CV minus than 2% (within-run), minus than 4% (run-to-run), interlaboratory CV minus than 5% (for 100 mumol/L creatinine). Inaccuracy evaluated for the chosen control sera is 1 to 15% as compared to the chromatographic method, according to the sera and to the analytical systems. The results obtained with the selected method are more consistent with the HPLC than are those obtained with an alkaline picrate method without SDS or with an enzymatic method. No interference could be demonstrated for acetoacetate (up to 8 mmol/L), hemoglobin (up to 210 mumol/L), unconjugated bilirubin (up to 250 mumol/L), glucose (up to 30 mmol/L), IgG (up to 45 g/L), albumin (up to 60 g/L). The effect of cephalosporins depends on the molecule. The reagents are stable for at least 6 months when stored in closed vials at +20 degrees C. The alkaline reagent is stable 30 days at +4 degrees C. Reference limits (0.025 and 0.975 fractiles) have been established for healthy adults. They are respectively 73 to 126 mumol/L for men and 59 to 100 mumol/L for females.

Reference values for serum zinc and selenium of French healthy children.

Age - and sex-specific reference intervals derived from a healthy pediatric population are presented for zinc, selenium and related analytes in serum. No strong correlations were found between age, sex and trace elements in serum. Serum variables were discussed to assess their ability as biochemical indicators of micronutrient status in the field of biological epidemiology.

Comparison of serum copper determination by colorimetric and atomic absorption spectrometric methods in seven different laboratories. The S.F.B.C. (Société Française de Biologie Clinique) Trace Element Group.

An interlaboratory collaborative trial was conducted on the determination of serum copper using two different methods, based on colorimetry (test combination Copper, Boehringer Mannheim, Mannheim, Germany) and flame atomic absorption spectrometry (FAAS). The general performance of the colorimetric method was below that of FAAS, except for sensitivity and linear range, as assessed by detection limit (0.44 versus 1.32 mumol/L) and upper limit of linearity (150 versus 50 mumol/L). The range of the between-run CVs and the recovery of standard additions were, respectively, 2.3-11.9% and 92-127% for the colorimetric method and 1.1-6.0% and 93-101% for the FAAS method. Interferences were minimal with both methods. The two techniques correlated satisfactorily (the correlation coefficients ranged from 0.945-0.970 among laboratories) but the colorimetric assay exhibited slightly higher results than the FAAS method. Each method was transferable among laboratories.

Laser immunonephelometry reference intervals for eight serum proteins in healthy children.

Eight serum proteins were analyzed with the Behring nephelometer in samples from 479 healthy French children, ages three to 16 years. Girls had higher concentrations of IgM and albumin than boys had. Age appeared to be a main factor of variation for the proteins tested. Reference intervals are presented for IgG, IgA, IgM, albumin, transthyretin (prealbumin), retinol-binding protein, alpha 1-acid glycoprotein, and C-reactive protein. The significance of increased concentrations of C-reactive protein within a community is discussed.

[Spectrometry emission by inductively coupled plasma (SEPIHF). Application in the determination of inorganic compounds]. / Spectrométrie d'émission par plasma à couplage inductif (SEPIHF). Application au dosage de composés inorganiques.

The authors describe the principle of inductively coupled argon plasma emission spectrometry (ICP) to determine inorganic compounds in biological samples. This method is compared with more classical electrothermal flame atomisation absorption spectrometry. The association of ICP with different instruments is reminded (HPLC, mass spectrometry, graphite furnace, hybride generation). Finally, the review ends with some applications in biological fluids.

[A model for evaluating screening tests. The case of colorectal tumors]. / Un modèle pour l'évaluation des tests de dépistage. Le cas des tumeurs colorectales.

The results of numerous studies on screening are restricted to crude estimates of the predictive value of different tests. This is notely the case for early diagnosis of colorectal adenoma and cancer. The reference examination is in principle a total colonoscopy. Usually, it is not performed on the subjects for which the screening test gives a negative result. Moreover, the distribution according to age and sex is not taken into account. Both variables are strongly associated with the prevalence of the disease. After a presentation of the problems arising from screening evaluation performed in such situations, a method is proposed for comparing different tests in several populations. An estimate of the expected number of cases within a fictitious control group matched for age and sex with the people whose the test result is positive is computed according to an hypothesis on the duration of asymptomatic cancer and using available descriptive data on symptomatic cancer incidence and on the prevalence of adenoma in the population. The selection power of the test, i.e. the number of observed cases divided by the number of expected cases, is proposed as a standardized parameter for measuring and comparing the validity of screening tests. The method is illustrated by an example of its application procedure. The discussion stresses the limitations of such an approach.

[Evaluation of an immunological test for detecting occult fecal blood for case-finding in colorectal tumors]. / Evaluation d'un test immunologique de recherche de sang dans les selles pour le dépistage des tumeurs colorectales.

Screening for colorectal tumours (cancers and polyps) by searching for blood in stools using the gaiac test is a well-known method. We evaluated a new gaiac test, the originality of which from its coupling with an enzyme immuno-assay specifically measuring human hemoglobin (Fecatest). The objectives of this new test were to decrease false positives and thus to improve the positive predictive value of screening. Subjects over 45 years of age attending health examinations at a Center of Preventive Medicine were studied. Of the 5,185 subjects who received the test, 4,376 (84 p. 100) performed it correctly, demonstrating good compliance in this population. For 664 (15 p. 100), the results of the gaiac test were positive. This positivity rate was higher for men than for women (20 p. 100 vs. 10 p. 100) but was not influenced by age. After positive results, 471 (70 p. 100) patients completed investigations decreasing the overall compliance to 80 p. 100. Fifteen cases of cancer and 78 cases of adenomas were found. The positive predictive value of the test was 20 p. 100 for tumours. A benign cause was found in 44 p. 100 of 471 patients, and investigations were negative in 36 p. 100. When the gaiac test was positive, the immunoenzymatic method significantly improved the positive predictive value for cancer (6 p. 100 vs. 3 p. 100) but not for polyps (20 p. 100 vs. 17 p. 100). Three of the 15 cancers and half of the 78 adenomas would not have been discovered with the immunoenzymatic method.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma uric acid: mass spectrometric method for control and comparison of intra- and interlaboratory studies.

We propose a preliminary study for the utilization of isotope dilution and mass fragmentography for the measurement of plasma uric acid. Using stable isotopes it is possible to measure this compound in comparison with the molecule labelled with three 15N atoms (1,3,9). We achieved the determination at the molecular peak. A linear calibration curve is obtained from standard solutions between 0 and 600 mumol/l. The method has good precision and the results obtained with different quality control materials demonstrate the need for better accuracy. This method could, after more detailed studies, be a good candidate for a definitive method.

Simultaneous determination of uric acid and creatinine in plasma by reversed-phase liquid chromatography.

Because numerous substances, endogenous compounds as well as xenobiotics, interfere with determination of uric acid and creatinine, we have devised a more nearly specific method by which we can simultaneously determine uric acid and creatinine in plasma by "high-performance" liquid chromatography. We used a mobile phase of ammonium acetate (30 mmol/L) and methanol (156 mmol/L) at pH 7.0 and a flow rate of 1 mL/min. We used a C18 reversed-phase column, and measured absorbance at 235 nm, the wavelength corresponding to the absorption maximum of uric acid and creatinine. Uric acid and creatinine could be determined in less than 5 min by directly injecting plasma diluted fivefold; use of a precolumn eliminated the need for deproteinization. We evaluated the precision, recovery, linearity, specificity, and limit of detection of the method and we checked for analytical interference by 37 currently used drugs. We compared results with those obtained by routine and reference methods.

Influence of turbidity on photometric assays: a blank sample must always be used.

The authors studied the influence of sample turbidity on photometric assays at different wavelengths. Turbidity was created by using a mixture of hydrazine sulfate and hexamethylene tetramine, and a dye solution (p-nitrophenol, cobalt nitrate). This work demonstrates the necessity of using a bland sample, for example in the glucose assay (glucose oxidase/peroxidase). The influence of turbidity on an assay depends upon the instrument. Knowledge of this influence is essential for the evaluation of the viability of an assay in hyperlipemic serum.

[Comparison of values, obtained on heparinised serum or plasma, for common biochemical examinations]. / Comparaison des valeurs obtenues sur sérum ou plasma hépariné pour les examens biochimiques courants

The biologist may prefer to use plasma rather than serum to facilitate sampling procedures in his laboratory. It is important to know whether or not the patients' results will be affected by this change. In daily practice, there is no difference to speak of between plasma and serum for bilirubin, calcium, potassium, creatinin, urea, cholesterol, sodium, uric acid, triglycerid and iron. There are, however, differences for total proteins, phosphates and glucose.