Uric Acid In Human Serum Research Articles

CuCo2S4 nanozyme-based stimulus-responsive hydrogel kit for rapid point-of-care testing of uric acid.

An efficient analysis platform composed of nanozyme-based hydrogel kit and smartphone was constructed for on-site detection of uric acid (UA) in a rapid and realiable manner. CuCo2S4 nanoparticles (CuCo2S4 NPs) as a peroxidase mimic were successfully prepared and the peroxidase-like activity and catalytic mechanism were studied in detail. The hydrogen peroxide (H2O2) stimulus-responsive nanozyme-based hydrogel kit was manufactured by integrating agarose, CuCo2S4 NPs, and 3,3',5,5'-tetramethylbenzidine (TMB) into the cap of centrifuge tube. H2O2 generated via UA oxidation acts as stimulus signal, which triggers the oxidation of TMB to form blue product (oxTMB) under the catalysis of CuCo2S4 NPs, resulting in the color response of the constructed kit. The color image of the kit was captured by a smartphone built-in camera and converted into color intensity using ImageJ software, thus achieving the quantitative determination of UA. The portable kit possesses high selectivity and was used to monitor UA in human serum with satisfactory results (recovery was in the range 95.8-107.3% and RSD was not greater than 4.6%). The established sensing platform is convenient and reliable, which provides a new strategy for point-of-care testing of UA and has a broad prospect in the fields of chemical sensing and biomedical.

Designed Mini Protein 20 Mimicking Uricase Encapsulated in ZIF-8 as Nanozyme Biosensor for Uric Acid Detection.

This work presents the use of encapsulated mini protein 20 mimicking uricase (mp20)-zeolitic imidazolate framework-8 (ZIF-8) as a bioreceptor for the development of a nanozyme-based electrochemical biosensor for uric acid detection. The electrochemical performance of the biofunctionalized mp20@ZIF-8 on the reduced graphene oxide/screen-printed carbon electrode (rGO/SPCE) was investigated by optimizing operating parameters such as pH, deposition potential, and deposition time using a central composite design-response surface methodology (CCD-RSM). The quadratic regression model was developed to correlate the combination of each variable to the oxidation current density as a response. A significant effect on current response was observed under optimized conditions of pH of 7.4 at −0.35 V deposition potential and 56.56 s deposition time, with p < 0.05 for each interacted factor. The obtained coefficient of determination (R2) value of 0.9992 indicated good agreement with the experimental finding. The developed nanozyme biosensor (mp20@ZIF-8/rGO/SPCE) exhibited high selectivity in the presence of the same fold concentration of interfering species with a detection limit of 0.27 μM, over a concentration range of 1 to 34 μM. The practicality of the tailored biosensor in monitoring uric acid in human serum and urine samples was validated with high-performance liquid chromatography (HPLC) and a commercial uric acid meter. Hence, nanozyme-based is a promising platform that offers a rapid, sensitive, selective, and low-cost biosensor for the non-enzymatic detection of uric acid in biological samples.

Determination of Uric Acid in Biological Fluids by Ceria Nanoparticles Doped Reduced Graphene Oxide Nanocomposite Voltammetric Sensor

High levels of uric acid (UA) in the human body usually cause diabetes, hypertension and atherosclerosis, kidney diseases, and neurological diseases. Hence, it is important to develop sensitive methods for UA determination. In this paper, nanocomposite composed of ceria nanoparticles and reduced graphene was successfully modified on the surface of glassy carbon electrode (ceria NPs-rGO/GCE) by a simple electroreduction method. The morphology, structure and property of the ceria NPs-rGO/GCE was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrocatalytic activity of the ceria NPs-rGO/GCE for uric acid (UA) oxidation was studied in detail. The results showed that the ceria NPs-rGO/GCE exhibited excellent selectivity and high sensitivity for UA detection. In 0.05 M H2SO4 solution, a linear range of 0.02–20 μM and a low detection limit of 8.0 nM of UA were obtained on the ceria NPs-rGO/GCE. This developed method was successfully applied for the detection of UA in human serum and urine samples, and its recoveries reached 95.8%-105.0%.

Novel and facile synthesis of heparin sulfur quantum dots via oxygen acceleration for ratiometric sensing of uric acid in human serum

In this work, a novel kind of sulfur quantum dots (SQDs) is synthesized using heparin as passivator and stabilizer for the first time by simple treatment of sublimed sulfur and NaOH under a pure oxygen atmosphere. The obtained heparin SQDs (Hep-SQDs) show excitation-independent emission and have a high quantum yield (11.4%). Herein, we set up a ratiometric fluorescence probe based on the inner filter effect between Hep-SQDs and 2, 3-diaminophenazine, the oxidative product of o-phenylenediamine to detect uric acid (UA). The proposed probe is demonstrated to be highly selective and sensitive for UA assay with detection limit of 0.56 μM. Moreover, the established fluorescence probe is also successfully applied to the determination of UA in human serum. We hope this work can provide new opportunities for developing good performance fluorescent biosensors based on SQDs.

A highly sensitive dual-read assay using nitrogen-doped carbon dots for the quantitation of uric acid in human serum and urine samples.

A simple dual-read assay for uric acid (UA) was developed based on a combined ratiometric fluorescent and colorimetric strategy using nitrogen-doped carbon dots (N-CDs). The biosensor relies on the oxidation of UA by uricase to produce H2O2, which was then converted to •OH radicals by I-, resulting in the oxidation of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP). In the presence of UA, the colorless biosensor system changed to yellow. Furthermore, the presence of DAP quenched the fluorescence emission of the N-CDs at 427 nm based on the inner filter effect (IFE). With increasing UA concentrations, the fluorescence intensity of the biosensor at 427 nm decreased but increased at 580 nm, demonstrating the ratiometric response. A strong linearity was observed between the fluorescence intensity ratio of DAP to N-CDs (I580/I427) and the corresponding UA concentration over the range 0.5−150 μM, and a limit of detection (S/N ratio of 3) of 0.06 μM was calculated. The dual-read assay was successfully employed in the quantitation of UA in human serum and urine samples, revealing its potential for measuring UA in clinical samples.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-021-04971-2.

Highly permselective uric acid detection using kidney cell membrane–functionalized enzymatic biosensors

Abnormal blood uric acid (UA) levels can lead to its crystallization in the joints, consequently resulting in gout. Accurate detection of UA in the blood is imperative for the early diagnosis of gout. However, electrochemical UA biosensors are vulnerable to antioxidants in the blood, limiting accurate UA detection. To address this issue, we focused on the function of uric acid transporter 1 (URAT1), which is selectively permeable to UA. URAT1 is abundant in the kidney cell membrane (KCM). To apply URAT1 to a sensor, we developed a KCM-coated UA biosensor (called the KCM sensor) that could selectively detect UA through URAT1. The KCM coating in the fabricated KCM sensor was verified via scanning electron microscopy, atomic force microscopy, and confocal microscopy. The KCM sensor enabled the detection of UA in the range of 0–1000 μM, with a limit of detection of 8.5 μM, suggesting that it allows the diagnosis of the early stages of gout. On the other hand, the UA permeability of the KCM sensor was significantly reduced in the presence of a URAT1 inhibitor, implying that URAT1 is a key factor for UA detection. The selectivity of the KCM sensor was demonstrated by measuring the amount for UA in the presence of various antioxidants. Finally, the KCM sensor was capable of measuring UA in human serum and was reproducible with 0.5–1.6% deviation. The UA permeability and selectivity of the KCM sensor were maintained even after 3 weeks of storage.

Colorimetric Detection of Uric Acid Based on Peroxidase-Like Activity of Ag2V4O11 Nanobelts

A colorimetric, rapid, and effective method for uric acid (UA) detection based on Ag2V4O11 nanobelts has been developed. Ag2V4O11 nanobelts were synthesized by a straightforward hydrothermal process, and proved to possess intrinsic peroxidase-like activity. The kinetic analysis illustrated that the reaction catalyzed by Ag2V4O11 nanobelts followed typical Michaelis–Menten kinetics. The results of active species trapping experiments suggested that superoxide radical (·O2−) played an important role in the reaction. The developed UA detection method showed a linear relationship from 1 μM to 110 μM with a detection limit of 0.35 μm. The results of selective experiments indicated that the method has a satisfactory detection selectivity on UA. Finally, the method was applied in the determination of UA in human serum, and the results were extremely close to the hospital results. This work would be indicative for the construction of Ag2V4O11 nanobelts in the application of UA determination. Schematic illustration of the colorimetric method for UA determination.

Visual and colorimetric detection of uric acid in human serum and urine using chitosan stabilized gold nanoparticles

In this paper, the chitosan stabilized gold nanoparticles was developed as a catalyzed 3,3′,5,5′-tetramethylbenzidine - H2O2 system for visual and colorimetric detection of uric acid. In theory, uric acid can be catalyzed by uricase to produce H2O2, and the chitosan stabilized gold nanoparticles were successfully synthesized by chemical reduction and showed an intrinsic peroxidase-like activity. The chitosan stabilized gold nanoparticles could effectively catalyze decomposition of H2O2 to generate OH radicals. The peroxidase substrate 3,3′,5,5′-tetramethylbenzidine is oxidized in the presence of OH radicals, resulting in a visible color change (from colorless to blue). This convenient, novel and sensitive method could be used for detection of uric acid based on the chitosan stabilized gold nanoparticles, with a linear range from 0.1 to 30 μM, and a limit of detection (S/N ratio of 3) as low as 0.04 μM. Furthermore, the detection method has been successfully applied to human serum and urine samples by visual observation. The recoveries of uric acid in human serum and urine were in the range of 96.1–103.1% and 95.2–97.7%, respectively. These results revealed that the visual colorimetric method may provide an alternative to clinical medicine and daily monitoring.

A convenient sampling and noninvasive dried spot method of uric acid in human saliva: Comparison of serum uric acid value and salivary uric acid in healthy volunteers and hyperuricemia patients

Concentration of uric acid (UA) in serum is one of the markers used to diagnose gout and hyperuricemia. However, serum treatment and storage are cumbersome, and wounds are susceptible to infection. Therefore, a new sampling and analysis method using noninvasive biological samples has been developed, called the dried spot method of UA in human saliva (DSM-UHS). Saliva (5 μL) was dropped on filter paper (a spot with a diameter of 5 mm) containing hypoxanthine (IS) (5 μL) and dried at room temperature for 30 min. The filter paper was immersed in 200 μL of lithium carbonate solution and shaken in a block bath shaker for 5 min at 30 °C. Afterward, the extraction was concentrated and reconstituted with 100 μL of lithium carbonate solution analyzed by HPLC-UV. When comparing the concentration of UA in the human saliva of hyperuricemia patients (HPs) and with that of healthy volunteers (HVs), we observed the concentration of UA was higher in the HPs than in the HVs (p < 0.0001). In addition, the results showed a significant linear relationship between the content of UA in saliva and the content of UA in the serum (r = 0.6243). The content of UA in human saliva could indirectly reflect the content of UA in human serum. Then DSM-UHS could be used to determine the content of UA in the saliva of HVs and HPs. This study provides a new research method and strategy for the determination of human UA content and the clinical prewiring of hyperuricemia.

The synergistic effect enhanced chemical etching of gold nanorods for the rapid and sensitive detection of biomarks

The rapid and sensitive assay is the goal for advancing analytical methods and techniques to save time and achieve the early diagnosis, which are of crucial importance in clinic. The concept of synergistic effects for fastening reaction and improving sensitivity was constructed by introducing iodide (I−) to the typical Fenton's reaction system as a model reaction, which was calculated theoretically and demonstrated experimentally. In an acid medium, the simultaneous presence of Fe2+ and I− could significantly improve the oxidation capability and rate of H2O2 to etch gold nanorods (AuNRs) because of the synergistic effect, which was further successfully applied to the rapid and sensitive assay of cholesterol, glucose and uric acid in human serum. In this work, the synergistic effect greatly improved the reaction rate and sensitivity, which showed potential applications in biological sensing and clinic diagnosis.

The effect of cadmium toxicity on Oreochromis niloticus and human health

Cadmium levels below permissible limits can be toxic, affecting the health of exposed aquatic organisms and ultimately human health. Although cause and effect links between aquatic organisms and human health have not been elicidated, this study evaluated the effect of cadmium exposure on the health status of Oreochromis niloticus and human fish consumers. Clinical and post-mortem examinations were performed in situ on fish samples collected monthly from the Abo-Saleh, Ehnasia fish farm and Nile River. Cadmium was measured in water and fish musculature from the two fish farms and in water samples from the Nile River. Human blood samples of consumers of fish from the two fish farms, as well as non-fish consumers as a control, were collected for estimation of cadmium, uric acid, creatinine and calcium levels. Clinical signs and post-mortem abnormalities of Oreochromis niloticus from Ehnasia fish farm showed congestion of gills, liver, intestine and spleen. Cadmium concentrations in water and musculatures of Oreochromis niloticus obtained from the Ehnasia fish farm was significantly higher than the permissible limit, whereas cadmium concentrations in the Abo-Saleh fish farm and Nile River were within the permissible limit. There were increased levels of cadmium in human blood and creatinine and uric acid in human serum, but decreased levels in calcium in serum of human consumers of fish from the Ehnasia fish farm. The presence of cadmium can be toxic, even at levels below the permissible limit, negatively affecting health, as observed for aquatic organisms and subsequently for humans.

Amperometric Detector of Uric Acid in Human Serum Based on Glassy Carbon Electrodes Modified By Gold Nanoparticles and Poly(amidoamine) Dendrimers and Its Application to the Early Diagnosis of Preeclampsia

Glassy carbon electrodes (GCE) were modified by cysteamine-capped gold nanoparticles (AuNp@cysteamine) and PAMAM dendrimers generation 4.5 bearing 128-COOH peripheral groups (GCE/AuNp@cysteamine/PAMAM), in order to be tested as electrochemical detector of uric acid (UA) in human serum samples. The results showed that concentrations of UA detected by cyclic voltammetry with GCE/AuNp@cysteamine/PAMAM were comparable (deviation <±10%; limits of detection and quantification were 1.7×10-4 and 5.8×10-4 mg/dL, respectively) to those concentrations obtained using the typical uricase-based enzymatic method [1]. Furthermore, results of UA detected by DC-potential amperometry demonstrated that the presence of dendrimers in the GCE/AuNp@cysteamine/PAMAM system minimizes ascorbic acid and serum proteins interferences during UA oxidation, thus improving the electrocatalytic activity of the gold nanoparticles. On the other hand, GCE/AuNp@cysteamine/PAMAM were employed for detecting UA in serum donated by pregnant women having gestational hypertension or preeclampsia (the group of “cases”) and from health pregnant women (the “control” group). The new data confirmed significant differences between the detected UA levels (p<0.001) in the groups of “cases” (6.2±0.5mg/dL) and “control” (4.2±0.9mg/dL), respectively. Therefore, these results demonstrated that the employment of GCE/AuNp@cysteamine/PAMAM - based amperometric detectors as non-enzymatic devices for early diagnosis of preeclampsia constitute a highly reliable route.

Colorimetric Detection of Uric Acid with High Sensitivity Using Cu2O@Ag Nanocomposites

In this paper, we built the Cu2O@Ag nanocomposites-catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB)–H2O2 system for sensitive, rapid, and low-cost colorimetric sensing of uric acid (UA). Firstly, Ag nanotriangles were synthesized by dynamic method, and then Cu2O was encapsulated on the nanoflakes to synthesize Cu2O@Ag nanocomposites. Characterization of the structure and morphology of nanocomposites material were characterized by transmission electron microscopy, X-ray energy-dispersive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Cu2O@Ag nanocomposites could catalyze the oxidation of TMB by H2O2 (which is produced by enzymatic oxidation of UA), and the color changes from colorless to blue can be observed directly with the naked eyes or can be detected by UV–Vis spectrophotometer. The colorimetric sensor provided a linear absorbance response in the 0.5–100 μM UA concentration range with a 0.4 μM detection limit (S/N = 3). The recovery of UA in human serum by the proposed sensor is over 95.7%. Thus, these results imply that the UA sensor provides an effective tool in fast clinical analysis of gout without the need for expensive and advanced equipment.

An Innovative Design of an Efficient Layered Electrochemical Sensor for Determination of Tyrosine and Tryptophan in the Presence of Interfering Compounds in Biological Fluids

The aromatic amino acids tyrosine (TY) and tryptophan (TP) are important as precursors of catecholamines and 5-hydroxytryptamine. An innovative strategy was proposed in preparation of a novel layered sensor based on layer-by-layer modification of a glassy carbon electrode surface (GC) with graphene (RGO), ionic liquid crystal (ILC), multi-walled carbon nanotubes (CNT) and Fe–Zn nano-alloy (GC/RGO/ILC/CNT/Fe–Zn). The conductive layered electrode offered good sensitivities and low detection limit values for determination of tyrosine (TY) and tryptophan (TP) due to the synergistic impact of its components. A major problem expected during electrochemical assays of TY or TP in human biological fluids is overlap of their current responses with ascorbic acid (AA) and uric acid (UA) compounds when using the unmodified electrodes. Thus, the proposed sensor resolved this problem and exhibited excellent electrocatalytic activity towards determination of TY or TP in presence of AA and UA in human serum with low detection limit values 5.1 nM, 86 nM, 2.6 nM for TY, AA and UA and 3.8 nM, 91 nM, 2.9 nM for TP, AA and UA, respectively. Moreover, the proposed sensor displayed good sensitivity towards simultaneous determination of dopamine (DA) and serotonin (ST) with TY or TP. Recovery tests of TY and TP compounds were successful.

Morphology-dependent MnO2/nitrogen-doped graphene nanocomposites for simultaneous detection of trace dopamine and uric acid.

Four nanostructured MnO2 with various controllable morphologies, including nanowires, nanorods, nanotubes and nanoflowers were synthesized, and then further composited with nitrogen-doped graphene (NG) with the assistance of ultrasonication. The surface morphologies, phase structures, and electrochemical performances of the proposed MnO2/NG nanohybrids were investigated by various techniques, and their catalytic activities on the electrooxidation of dopamine (DA) and uric acid (UA) were compared systematically. The sensing performances were found to be highly correlated with their morphologies. Among these morphologies, the nanoflower-like MnO2, composited with NG, displayed the most sensitive response signals for DA and UA. The boosted electrocatalytic activity was ascribed to the unique porous structure, large electroactive area, and low charge transfer resistance (Rct), which facilitated the electron transfer between electrode and analytes. Two linear response ranges (0.1μM-10μM and 10μM-100μM) were accompanied with very low detection limits of 34nM and 39nM for DA and UA, respectively. Moreover, the successful application of the MnO2NFs/NG composites for the simultaneous detection of DA and UA in human serum was realized using second-derivative linear sweep voltammetry (SDLSV). These findings give valuable insights for understanding the morphology-dependent sensing properties of MnO2 based nanomaterials, which is conducive to the rapid development of ubiquitous MnO2-based electrochemical sensors.

Atomic matching catalysis to realize a highly selective and sensitive biomimetic uric acid sensor

A main challenge for biomimetic non-enzyme biosensors is to achieve high selectivity. Herein, an innovative biomimetic non-enzyme sensor for electrochemical detection of uric acid (UA) with high selectivity and sensitivity is realized by growing Prussian blue (PB) nanoparticles on nitrogen-doped carbon nanotubes (N-doped CNTs). The enhancement mechanism of the biomimetic UA sensor is proposed to be atomically matched active sites between two reaction sites (oxygen atoms of 2, 8-trione, 6.9 Å) of UA molecule and two redox centers (FeII on the diagonal, 7.2 Å) of PB. Such an atomically matching manner not only promotes strong adsorption of UA on PB but also selectively enhances electron transfer between reaction sites of UA and active FeII centers of PB. This biomimetic UA sensor can offer great selectivity to avoid interferences from other oxidative and reductive species, showing excellent selectivity. An electrochemical biomimetic sensor based on PB/N-doped CNTs was applied to in situ detect UA in human serum, delivering a wide dynamic detection range (0.001–1 mM) and a low detection limit (0.26 μM). This work provides a high-performance UA sensor while shedding a scientific light on using atomic matching catalysis to fabricate highly sensitive and selective biomimetic sensors.

Morphology-Dependent Electrochemical Sensing Properties of Iron Oxide-Graphene Oxide Nanohybrids for Dopamine and Uric Acid.

Various morphologies of iron oxide nanoparticles (Fe2O3 NPs), including cubic, thorhombic and discal shapes were synthesized by a facile meta-ion mediated hydrothermal route. To further improve the electrochemical sensing properties, discal Fe2O3 NPs with the highest electrocatalytic activity were coupled with graphene oxide (GO) nanosheets. The surface morphology, microstructures and electrochemical properties of the obtained Fe2O3 NPs and Fe2O3/GO nanohybrids were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. As expected, the electrochemical performances were found to be highly related to morphology. The discal Fe2O3 NPs coupled with GO showed remarkable electrocatalytic activity toward the oxidation of dopamine (DA) and uric acid (UA), due to their excellent synergistic effect. The electrochemical responses of both DA and UA were linear to their concentrations in the ranges of 0.02–10 μM and 10–100 μM, with very low limits of detection (LOD) of 3.2 nM and 2.5 nM for DA and UA, respectively. Moreover, the d-Fe2O3/GO nanohybrids showed good selectivity and reproducibility. The proposed d-Fe2O3/GO/GCE realized the simultaneous detection of DA and UA in human serum and urine samples with satisfactory recoveries.

Standard addition method with cumulative additions: Monte Carlo uncertainty evaluation

The cumulative standard addition method allows the calibration of an instrument affected by matrix effects when a small sample volume is available. Recently, it was developed and validated a metrologically sound procedure to estimate the uncertainty of these measurements based on the modelling of the uncertainty of the extrapolation of the calibration curve by the linear least squares regression model. However, this procedure is only applicable when the uncertainty of cumulative sample dilutions and analyte mass additions are negligible given the uncertainty of the total solution volume (v) times the instrumental signal (I) (i.e. v∙I). This work developed a measurement uncertainty model, not limited by this assumption of the quality of calibrators preparation, based on Monte Carlo simulations. This method was successfully applied to the voltammetric measurements of uric acid in human serum, using a working nanocarbon electrode modified with Cu-nanocarbon-lignin, since the uncertainty model adapts to the uncertainty of cumulative volume additions. The validated procedure was checked through the analysis of spiked physiological serum samples and human serum samples, by assessing the metrological compatibility between estimated and reference values. The measurements are reported with an expanded uncertainty not larger than a target value of 0.56 mg dL−1. The used spreadsheet is made available as supplementary material.

Comparison of CRMs and value-assigned quality controls: urea and uric Acid in human serum or plasma (CCQM-K142)

The CCQM OAWG 2017 CCQM-K142 "Comparison of CRMs and Value-Assigned Quality Controls: Urea and Uric Acid in Human Serum or Plasma" is the third Model 2 Key Comparison coordinated by the OAWG directly testing the chemical measurement services provided to customers by National Metrology Institutes (NMIs) and Designated Institutes (DIs) through certified reference materials (CRMs). CRMs certified for urea and/or uric acid content in human serum or plasma were compared using measurements made on these materials under repeatability conditions. Four NMIs/DIs submitted 10 CRMs certified for urea; five NMIs/DIs submitted 12 CRMs certified for uric acid. These materials represent most of the higher-order reference materials available then for these clinically important measurands. Uncertainty-weighted generalised distance regression was used to establish the Key Comparison Reference Function (KCRF) relating the CRM certified values to the repeatability measurements. The urea results for all 10 CRMs were considered to be equivalent at the 95 % level of confidence and were used to define the KCRF for urea. The uric acid result for one of the 12 CRMs was found to be non-equivalent: the submitting NMI re-evaluated the result and withdrew the material from use in defining the KCRF for uric acid. The remaining 11 CRMs were used to define the KCRF for uric acid. Monte Carlo methods were used to estimate 95 % level-of-confidence coverage intervals for the relative degrees of equivalence of materials, %d ± U95 (%d), and of the participating NMIs/DIs, %D ± U95 (%D). For the urea materials, the %D ± U95(%D) intervals were within (-3 to 5) % of the consensus results. For the uric acid materials from four of the five NMIs/DIs, the %D ± U95(%D) intervals were within (-4 to 5) % of the consensus results. These results demonstrated that with the exception of one material, the participating institutions could value-assign CRMs for urea and/or uric acid in human serum and plasma.KEY WORDS FOR SEARCHCertified reference materials; urea; uric acid; human serum; key comparison reference functionMain textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

High polarity analytes in biological matrix: determination of urea and uric acid in human serum (CCQM-K109)

The CCQM Organic Analysis Working Group (OAWG) agreed on a Track A comparison for the measurement of polar organic in biological matrix as part of its 10-year strategic plan. As a model for this comparison, two polar clinical biomarkers: urea and uric acid, in human serum were chosen. This comparison was designed to enable participating National Metrology Institutes (NMIs) or Designated Institutes (DIs) to demonstrate their measurement capabilities in the determination of analytes with molecular mass of 50 to 500 g/mol, having the polarity pKOW > 2 in the range of 10 to 2,000 mg/kg in a biological matrix such as human serum, blood and urine. Two pools of human serum materials with different concentration levels of urea and uric acid were used as the comparison materials. Fifteen NMIs/DIs participated in this Track A comparison. All of them submitted the results for urea and 14 NMIs/DIs submitted the results for uric acid. With the exception of one NMI, all participating institutes employed isotope dilution mass spectrometry (IDMS) for the measurement of both urea and uric acid. Protein precipitation, liquid-liquid extraction and/or clean-up were applied, followed by instrumental analyses using GC-HRMS, GC-MS/MS, GC-MS, LC-HRMS, LC-MS/MS, LC-MS or HPLC-DAD. The Laplacian weighted medians were used as the Key Comparison Reference Values (KCRVs). The assigned KCRVs were the weighted medians of 13 results for urea (both serum pools), 10 results for uric acid (Serum I) and 11 results for uric acid (Serum II). Urea (Serum I) was assigned a KCRV of 1,486.0 mg/kg with a standard uncertainty of 9.0 mg/kg, urea (Serum II) was assigned a KCRV of 334.7 mg/kg with a standard uncertainty of 1.8 mg/kg, uric acid (Serum I) was assigned a KCRV of 136.50 mg/kg with a standard uncertainty of 0.98 mg/kg, and uric acid (Serum II) was assigned a KCRV of 39.39 mg/kg with a standard uncertainty of 0.11 mg/kg. The degree of equivalence (with the KCRV) and its uncertainty were calculated for each result. The majority of the participating institutes in CCQM-K109 demonstrated their capabilities in the measurement of the clinical markers in the biological matrix using IDMS.KEY WORDS FOR SEARCHClinical biomarkers; urea; uric acid; human serum, IDMSMain textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).