A metrological approach for the assessment of selenium status in human serum

This work addresses a metrological approach for the assessment of Se status in humans in terms of serum selenomethionine (SeMet). The quantification of SeMet was carried out using a primary method of chemical analysis, namely species-specific isotope dilution (SSID) in combination with HPLC coupled to collision/reaction cell inductively coupled plasma-mass spectrometry. SeMet was released from the serum selenoalbumin (a seleno-containing protein where SeMet is randomly incorporated) by enzymatic hydrolysis of the whole serum. This study is a follow-up of the analytical method development reported previously, and it focuses primarily on the evaluation of the uncertainty budget and the main uncertainty sources for SeMet determination in three commercial serums, namely BCR-637 (certified for total Se) and two serum standards, SERONORM level 1 (SERO-L1) and 2 (SERO-L2) (with indicative concentrations of total Se). The metrological approach reported here could be considered as a pilot study in terms of metrological determination of SeMet in human serum, hence being suitable for method validation and inter-laboratory comparison.     

Standardization and improvement program for creatinine measurement in human serum

Accreditation and Quality Assurance - Current practices, quality control systems and proficiency testing schemes in clinical laboratories are likely unable to detect intrinsic bias in the in vitro...     

The impact of metrological traceability on the validity of creatinine measurement as an index of renal function

When the calibration of a routine measurement procedure is traced back to metrological higher order, a significant discrepancy can occur between the analytical conditions of the routine measurement and the analytical conditions that were used in the clinical studies upon which the decision-making criteria are based. This can lead to serious interpretation errors with possible dramatic consequences for patients. The calibration of the creatinine Jaffé method is an excellent example of the importance of medical traceability. The compensated Jaffé method correlated accurately with the reference method and the compensated Jaffé creatinine clearance (CrCl), Cockroft and Gault and MDRD with the ⁵¹Cr EDTA clearance. The Schwartz estimate based upon the compensated Jaffé and enzymatic method overestimated, while uncompensated Jaffé slightly underestimated glomerular filtration rate (GFR). The situation in children is complex since serum creatinine concentrations are much lower in infants, rendering tubular secretion relatively more important. Low-molecular weight proteins have been suggested to replace serum creatinine as a marker for GFR. -trace protein, cystatin C, and ₂-microglobulin showed good correlation with GFR. However, care should be taken in patients presenting with some malignant tumors, since significant increases of cystatin C in patients with metastatic melanoma or colorectal cancer has been reported.Presented at the 9th Conference on Quality in the Spotlight, 18-19 March 2004, Antwerp, Belgium     

Stopped-flow determination of creatinine in human serum and food samples

Summary The results obtained by applying a modular stopped-flow system for the determination of creatinine by the alkaline picrate method are reported. The stopped-flow technique allows the simple and rapid determination of creatinine in human serum and food samples. The calibration graph is linear in the range 1–100 g ml^–1 of creatinine and the precision is close to 3%. The method features acceptable selectivity. The initial rate is measured in only 5 s, which allows the easy application of the method to routine analyses. No pretreatment of the serum samples is required. For food samples, total creatine and creatinine have been determined in dehydrated soup and meat extract samples.

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Stopped-flow-Bestimmung von Creatinin in Humanserum und Nahrungsmitteln

     

An improved kinetic determination for creatinine using the Abbott ABA-100

An improved method for the kinetic determination of creatinine on the Abbott ABA-100 is described. By simplex optimization of the picrate and hydroxide reaction concentration a 35% increase in reaction rate, with respect to the Abbott methodology, was obtained. The new method correlated more closely with the Technician AutoAnalyzer Method (N-30) than did the latter method. The percentage CV for the improved method for high and low quality control sera was 2.4 and 3.6%, respectively. The presence of protein in the standards was found to cause a decrease in the reaction rate with respect to aqueous standards.     

The consequences of the mutual recognition of measurement standards for international metrology

After stressing the importance in the modern world of accurate and reproducible measurements, the actions taken by the Bureau International des Poids et Mesures to set up, together with the regional metrology organizations, a series of key comparisons are described. They are the technical foundation of a mutual recognition of national measurement standards arrangement prepared in conjunction with the National Metrology Institutes (NMIs). This arrangement also includes the recognition of calibration and measurement certificates issued by these institutes. Then, the consequences of this arrangement for trade are described. The case of chemical analysis is illustrated by the application of the Kyoto protocol on the reduction of greenhouse gases. But the global workload to be taken up by the International Committee of Weights and Measures, its Consultative Committee for Amount of Substance and the NMIs is huge.     

The consequences of the mutual recognition of measurement standards for international metrology

 After stressing the importance in the modern world of accurate and reproducible measurements, the actions taken by the Bureau International des Poids et Mesures to set up, together with the regional metrology organizations, a series of key comparisons are described. They are the technical foundation of a mutual recognition of national measurement standards arrangement prepared in conjunction with the National Metrology Institutes (NMIs). This arrangement also includes the recognition of calibration and measurement certificates issued by these institutes. Then, the consequences of this arrangement for trade are described. The case of chemical analysis is illustrated by the application of the Kyoto protocol on the reduction of greenhouse gases. But the global workload to be taken up by the International Committee of Weights and Measures, its Consultative Committee for Amount of Substance and the NMIs is huge.

     

From total allowable error via metrological traceability to uncertainty of measurement of the unbiased result

The concept of "total allowable error", investigated by Westgard and co-workers over a quarter of a century for use in laboratory medicine, comprises bias as well as random elements. Yet, to minimize diagnostic misclassifications, it is necessary to have spatio-temporal comparability of results. This requires trueness obtained through metrological traceability based on a calibration hierarchy. Hereby, the result is associated with a final uncertainty of measurement purged of known biases of procedure and laboratory. The sources of bias are discussed and the importance of commutability of calibrators and analytical specificity of the measurement procedure is stressed. The practicability of traceability to various levels and the advantages of the GUM approach for estimating uncertainty are shown.     

Point of care creatinine measurement for diagnosis of renal disease using a disposable microchip

A point‐of‐care device for the determination of elevated creatinine levels in blood is reported. This device potentially offers a new and simple clinical regime for the determination of creatinine that will give huge time savings and removal of several steps of determination. The test employs a disposable prefilled microchip and the handheld Medimate Multireader®. By optimizing the analytical conditions it was found that the LOD of the proposed method was 87 μM creatinine, close to the normal human serum levels that are in the range of 60 to 100 μM. A statistical analysis of the residual shows a normal distribution, indicating the absence of systematic errors in the proposed method. The test can be used to distinguish patients with renal insufficiency (creatinine levels >100 μM) from healthy persons. Long‐term monitoring could furthermore distinguish between acute renal failure and chronic kidney disease by the rate of creatinine concentration rise.     

A system of metrological assurance of measurement quality for the determination of chemical composition of light alloys and superalloys

 The paper covers the main principles of setting up and the function of the Russian system of metrological assurance of analytical measurements for the production of light alloys and superalloys. Received: 20 October 1998 / Accepted: 9 November 1998     

Alternative method for measurement of albumin/creatinine ratio using spectrophotometric sequential injection analysis

A simple, automatic and practical system for successive determination of albumin and creatinine has been developed by combining sequential injection analysis (SIA) and highly sensitive dye-binding assays. Albumin detection was based on the increase in the absorbance due to complex formation between albumin and eosin Y in acidic media. The absorbance of the complex was monitored at 547 nm. For the creatinine assay, the concentration of creatinine was measured by reaction with alkaline picrate to form a colored product which absorbs at 500 nm. The influences of experimental variables such as effects of pH, reagent concentration, standard/sample volume and interferences were investigated. Under optimal conditions, the automated method showed linearity up to 20 mg L⁻¹ for albumin and 100 mg L⁻¹ for creatinine. The 3σ detection limits were 0.6 and 3.5 mg L⁻¹ for albumin and creatinine, respectively, and the relative standard deviations (n = 10) were 2.49% for 20 mg L⁻¹ albumin, and 3.14% for 20 mg L⁻¹ creatinine. Application of the proposed method to the direct analysis of urinary samples yielded results which agreed with those obtained from the Bradford protein assay and a creatinine enzymatic assay according to a paired t-test. The results obtained should be a step towards developing a fully automated and reliable analytical system for clinical research, which requires direct determination of albumin and creatinine and/or its ratios.     

An international intercalibration for methylmercury in biological tissue

An intercalibration exercise between 13 laboratories from seven countries was conducted for comparing the methylmercury measurement techniques for marine biological tissues. Analyses have been conducted on two sets of samples: a fish muscle and a mussel soft tissue. Most of the participating laboratories performed six replicate analyses, allowing statistical comparisons. Various analytical techniques have been used, including cold vapour atomic absorption spectrophotometry (CVAA), electron capture gas liquid chromatography (GCEC), neutron activation (NAA), and inductively coupled plasma–isotopic dilution mass spectrometry (ICPIDMS). All of these methods offer similar results. They allow us to define consensus values which seem good estimates of the real concentrations. In addition the results show, for most of the participating laboratories, good accuracy and precision in the determination.     

Determination of creatinine in human serum by short-end injection capillary zone electrophoresis

A new ultra-rapid free-solution capillary zone electrophoresis method to measure serum creatinine is presented. Procedural parameters such as injection mode, concentration and pH of phosphate running buffer and acidic deproteinization of serum samples were investigated. Short-end injection permits a decrease of the analysis time by injecting samples at the outlet end of a silica capillary closest to the detection window, so reducing the migration distance. Thus, when a capillary with an effective length of 10.2 cm and a 40 mmol/L sodium phosphate buffer pH 2.35 was used, the obtained migration time of the creatinine peak was the shortest never described before, about 1.1 min. These conditions give a good reproducibility of the migration times (coefficient of variation, CV% < 0.5) and the peak areas (CV% < 2.8). Intra- and interassay CV were 3.06 and 6.26%, respectively, and analytical recovery was 99.4%. We compared our proposed method to Jaffé colorimetric assay, by measuring serum creatinine in 128 normal subjects. The obtained data were analyzed by the Passing and Bablok regression and Bland-Altman test. Creatinine concentration in healthy subjects was also used to investigate on its relationships with plasma thiols levels.