Multivariate anomaly detection models enhance identification of errors in routine clinical chemistry testing.

OBJECTIVES: Conventional autoverification rules evaluate analytes independently, potentially missing unusual patterns of results indicative of errors such as serum contamination by collection tube additives. This study assessed whether multivariate anomaly detection algorithms could enhance the detection of such errors. METHODS: Multivariate Gaussian, k-nearest neighbours (KNN) distance, and one-class support vector machine (SVM) anomaly detection models, along with conventional limit checks, were developed using a training dataset of 127,451 electrolyte, urea, and creatinine (EUC) results, with a 5 % flagging rate targeted for all approaches. The models were compared with limit checks for their ability to detect atypical EUC results from samples spiked with additives from collection tubes: EDTA, fluoride, sodium citrate, or acid citrate dextrose (n=200 per contaminant). The study additionally assessed the ability of the models to identify 127,449 single-analyte errors, a potential weakness of multivariate models. RESULTS: The KNN distance and SVM models outperformed limit checks for detecting all contaminants (p-values <0.05). The multivariate Gaussian model did not surpass limit checks for detecting EDTA contamination but was superior for detecting the other additives. All models surpassed limit checks for identifying single-analyte errors, with the KNN distance model demonstrating the highest overall sensitivity. CONCLUSIONS: Multivariate anomaly detection models, particularly the KNN distance model, were superior to the conventional approach for detecting serum contamination and single-analyte errors. Developing multivariate approaches to autoverification is warranted to optimise error detection and improve patient safety.

Evaluation of a flow cytometric test for G6PD-deficient erythrocytes.

OBJECTIVE: Glucose-6-phosphate dehydrogenase (G6PD) deficiency, an X-linked recessive disorder, is the commonest erythrocytic enzymopathy worldwide. Reliable diagnosis and severity prediction in G6PD-deficient/heterozygous females remain challenging. A recently developed flow cytometric test for G6PD deficiency has shown promise in precisely identifying deficient females. This paper presents our experiences with this test in a subtropical setting and presents a modification in flow cytometric data acquisition strategy. METHODS: The methaemoglobin reduction + ferryl Hb generation-based flow cytometric G6PD test was compared with the screening methaemoglobin reduction test (MRT) and confirmatory G6PD enzyme activity assay (EAA) in 20 G6PD-deficient males, 22 G6PD-heterozygous/deficient females and 20 controls. Stained cells were also assessed for bright/dim G6PD activity under a fluorescent microscope. RESULTS: Flow cytometry separated and quantified %bright cells in heterozygous/deficient females, objectively classifying them into 6 normal (>85% bright cells), 14 intermediate (10-85%) and two G6PD-deficient (<10% bright cells). Concordance with MRT was 89% (55/62 cases) and with EAA was 77% (48/62 cases). Fluorometrically predicted violet laser excitation (405-nm) with signal acquisition in the 425-475 nm region was a technical advancement noted for the first time in this paper. CONCLUSION: Flow cytometry/fluorescence microscopy represent technically straightforward methods for the detection and quantification of G6PD-deficient erythrocytes. Based on our results, we recommend their application as a first-line investigation to screen females who are prescribed an oxidant drug like primaquine or dapsone.

Implementation of patient-based real-time quality control.

The quest to use patient results as quality control for routine clinical chemistry testing has long been driven by issues of the unavailability and cost of suitable quality control material and the matrix effects of synthetic material. Hematology laboratories were early adopters of average of normals techniques, primarily because of the difficulty in acquiring appropriate, stable quality control material, while in the chemistry laboratories, the perceived advantages and availability of synthetic material outweighed the disadvantages. However, the increasing volume of testing in clinical chemistry plus the capability of computer systems to deal with large and complex calculations has now made the use of patient-based quality control algorithms feasible. The desire to use patient-based quality control is also driven by increasing awareness that common quality control rules and frequency of analysis may fail to detect clinically significant assay biases. The non-commutability of quality control material has also become a problem as laboratories seek to harmonize results across regions and indeed globally. This review describes the history of patient-based quality control in clinical chemistry, summarizes the various approaches that can be implemented by laboratory professionals, and discusses how patient-based quality control can be integrated with traditional quality control techniques.

Non-Parametric Combined Reference Regions and Prediction of Clinical Risk.

BACKGROUND: Many clinical decisions depend on estimating patient risk of clinical outcomes by interpreting test results relative to reference intervals, but standard application of reference intervals suffers from two major limitations that reduce the accuracy of clinical decisions: (1) each test result is assessed separately relative to a univariate reference interval, ignoring the rich pathophysiologic information in multivariate relationships, and (2) reference intervals are intended to reflect a population's biological characteristics and are not calibrated for outcome prediction. METHODS: We developed a combined reference region (CRR), derived CRRs for some pairs of complete blood count (CBC) indices (RBC, MCH, RDW, WBC, PLT), and assessed whether the CRR could enhance the univariate reference interval's prediction of a general clinical outcome, 5-year mortality risk (MR). RESULTS: The CRR significantly improved MR estimation for 21/21 patient subsets defined by current univariate reference intervals. The CRR identified individuals with >2-fold increase in MR in many cases and uniformly improved the accuracy for all five pairs of tests considered. Overall, the 95% CRR identified individuals with a >7× increase in 5-year MR. CONCLUSIONS: The CRR enhances the accuracy of the prediction of 5-year MR relative to current univariate reference intervals. The CRR generalizes to higher numbers of tests or biomarkers, as well as to clinical outcomes more specific than MR, and may provide a general way to use existing data to enhance the accuracy and precision of clinical decisions.

Preparation of In-House Quality Control Human Serum for Urea and its Use in Clinical Chemistry.

BACKGROUND: Quality control materials play a vital role in the laboratory internal and external quality assessment program. However, Ethiopia and other developing countries are challenged by the unavailability and high cost of commercial control material. Therefore, preparing in-house quality control human serum will be a cost-effective way to obtain QC material for use in poor settings in a country like Ethiopia. To prepare urea in-house control human serum and scientifically evaluate it with commercially available sera already in use in the clinical chemistry laboratory of the Ethiopian Public Health Institute. METHODS: The urea in-house quality control human serum was prepared as per ISO Guide 80, a guideline document protocol from 57 participants' normal serum specimens at the Ethiopian Public Health Institute clinical chemistry laboratory. The quality control material was analyzed on a fully automated chemistry analyzer (Cobas 6000). The initial 20 values were used for calculation of means, standard deviation (SD) and coefficient of variation (CV). Results were compared with those of commercially available lyophilized human sera. RESULTS: The average concentrations of urea were found to be near the middle of the physiological range of healthy subjects and the in-house serum could be a good substitute for the commercial serum of normal range. The prepared in-house quality control human serum is stable for about three months without any alterations in the concentration of urea. CONCLUSIONS: Well prepared in-house quality control human serum is a good substitute for commercially available control serum of normal range, especially in a developing country like Ethiopia.

Application and optimization of reference change values for Delta Checks in clinical laboratory.

BACKGROUND: Delta check is a patient-based QC tool for detecting errors by comparing current and previous test results of patient. Reference change value (RCV) is adopted in guidelines as method for delta check, but the performance is not verified. We applied RCV-based delta check method to patients' data and modified for application. MATERIALS AND METHODS: Reference change value were calculated using results of internal QC materials and biological variation data. Test results of 17 analytes in inpatients, outpatients, and health examination recipients were collected. The detection rates of currently used delta check method and those of RCV-based method were compared, and the methods were modified. RESULTS: Reference change value-based method had higher detection rates compared to conventional method. Applied modifications reduced detection rates. Removing the pairs of results within reference interval reduced detection rates (0.42% ~ 10.92%). When RCV was divided by time interval, the detection rates were similar to prior rates in outpatients (0.19% ~ 1.34%). Using RCV multiplied by twice the upper limit of reference value as cutoff reduced the detection rate (0.07% ~ 1.58%). CONCLUSIONS: Reference change value is a robust criterion for delta check and included in clinical laboratory practice guideline. However, RCV-based method generates high detection rates which increase workload. It needs modification for use in clinical laboratories.

Update on low-density lipoprotein cholesterol quantification.

PURPOSE OF REVIEW: ß-Quantification is considered the reference measurement procedure for low-density lipoprotein cholesterol (LDL-C). However, this technique is time-consuming and thus is inappropriate for routine clinical practice. Therefore, the Friedewald equation or homogeneous assays have been widely utilized. As several pitfalls exist with these two methods, a novel method for estimating LDL-C was developed by Martin et al. RECENT FINDINGS: Martin's method uses a strata-specific median for the triglycerides/very low-density lipoprotein cholesterol (VLDL-C) ratio on the basis of triglycerides and non-HDL-C concentrations. Recent studies show that Martin's method better correlates with ß-quantification or homogeneous assays compared with the Friedewald equation, especially with values of triglycerides at least 150 mg/dl and/or LDL-CD less than 70 mg/dl. Such findings have also been demonstrated in other ethnic groups (Japanese and Korean) and disease populations, including diabetes and cardiovascular disease, in which the triglycerides/VLDL-C ratio can be affected. SUMMARY: For the current therapeutic goal of LDL-C values below 70 mg/dl in high-risk patients, accurate assessment of LDL-C levels at very low levels is required. Martin's method could overcome pitfalls such as underestimation of the Friedewald equation at this level. Further evaluation of the triglycerides/VLDL-C ratio in participants with diverse ethnic backgrounds or clinical conditions would expand the implementation of this novel method.

Evaluation of procalcitonin immunoassay concordance near clinical decision points.

Background Procalcitonin (PCT) is a biomarker for systemic bacterial infections and may aid in decision making for antimicrobial stewardship. Numerous PCT assays are available on common clinical immunoassay platforms. However, questions remain about the harmonization of these assays and whether the same clinical decision points may be used with all methods. Methods Thirty-seven remnant patient serum samples were analyzed across four different PCT assays: Abbott ARCHITECT i2000, bioMérieux MINI VIDAS, Roche Elecsys cobas e 411, and BRAHMS KRYPTOR. Regression analysis was performed, and correlation was assessed at common clinical decision points for antimicrobial therapy: 0.10, 0.25, and 0.50 µg/L. Results Data showed a positive bias of the MINI VIDAS compared to the KRYPTOR (slope=1.188, R=0.9873) and negative biases of both the ARCHITECT i2000 and cobas e 411 compared to the KRYPTOR (slope=0.806, R=0.8864, and slope=0.795, R=0.8974, respectively). A comparison of results at commonly used clinical decision points for antimicrobial stewardship showed that, relative to the KRYPTOR, 21% of samples would be classified into different interpretive categories by the ARCHITECT i2000 method, 31% of samples would be classified differently by the MINI VIDAS method, and 16% of samples would be classified differently by the cobas e 411 method. Conclusions All methods showed reasonable analytical agreement; however, an analysis of result interpretation at clinical decision points showed that many samples were differentially categorized (e.g. shifted by one interpretive category) by the methods. Overall, our findings support a need for harmonization of PCT methods. Until then, institutions should independently evaluate their PCT assays against predicate methods and consider the impact on result interpretation prior to incorporating PCT into clinical practice.

Analytical validation of an in-house method for adenosine deaminase determination.

BACKGROUND: The adenosine deaminase (ADA) enzyme is a marker of inflammatory processes whose activity can be measured through a colorimetric method developed as an in-house assay. This validation can reduce costs and expand the alternatives for laboratory diagnosis. METHODS: The ADA analysis was achieved through a modified form of Giusti and Galanti's (1984) method. The following parameters were characterized: calibration curve, linearity, analytical sensitivity, limit of detection, limit of quantification, method working range, precision (within-assay and between-assay), bias, total analytical error, and sample stability. The results were statistically evaluated and compared with quality specifications based on biological variations and the performance of commercial tests. RESULTS: The analytical sensitivity and limit of detection (0.013 and 3.0 U/L, respectively) were lower than those of commercial tests. The method's working range was 3.2-100.0 U/L. According to the quality specification, the method showed optimum performance with a bias <3.5%. However, repeatability (2.2% and 1.7% for normal- and high-activity samples, respectively) and reproducibility achieved worse results when compared to commercial tests. The method demonstrated an inappropriate between-assay precision for low enzymatic activity (10.4%) and the minimum and desirable performance for medium (8.8%) and high (5.0%) activities, respectively. It also presented at least a minimum performance (<25%) for the total analytical error of the three analyzed samples. The pleural fluid samples were found to be stable at -20°C for six days. CONCLUSION: The findings show that the in-house method displays an acceptable performance and is capable of generating results comparable to existing commercial tests.

Sample management for clinical biochemistry assays: Are serum and plasma interchangeable specimens?

The constrained economic context leads laboratories to centralize their routine analyses on high-throughput platforms, to which blood collection tubes are sent from peripheral sampling sites that are sometimes distantly located. Providing biochemistry results as quickly as possible implies to consolidate the maximum number of tests on a minimum number of blood collection tubes, mainly serum tubes and/or tubes with anticoagulants. However, depending on the parameters and their pre-analytical conditions, the type of matrix - serum or plasma - may have a significant impact on results, which is often unknown or underestimated in clinical practice. Importantly, the matrix-related effects may be a limit to the consolidation of analyses on a single tube, and thus must be known by laboratory professionals. The purpose of the present critical review is to put forward the main differences between using serum and plasma samples on clinical biochemistry analyses, in order to sensitize laboratory managers to the need for standardization. To enrich the debate, we also provide an additional comparison of serum and plasma concentrations for approximately 30 biochemistry parameters. Properties, advantages, and disadvantages of serum and plasma are discussed from a pre-analytical standpoint - before, during, and after centrifugation - with an emphasis on the importance of temperature, delay, and transport conditions. Then, differences in results between these matrices are addressed for many classes of biochemistry markers, particularly proteins, enzymes, electrolytes, lipids, circulating nucleic acids, metabolomics markers, and therapeutic drugs. Finally, important key-points are proposed to help others choose the best sample matrix and guarantee quality of clinical biochemistry assays. Moreover, awareness of the implications of using serum and plasma samples on various parameters assayed in the laboratory is an important requirement to ensure reliable results and improve patient care.

Phosphonate-Substituted Ruthenium(II) Bipyridyl Derivative as a Photoelectrochemical Probe for Sensitive and Selective Detection of Mercury(II) in Biofluids.

A ruthenium(II) bipyridyl derivative photoelectrochemical probe, Ru-1, is synthesized and coupled with TiO2 nanoparticles (Ru-1/TiO2) for the specific recognition and highly sensitive photoelectrochemical (PEC) detection of Hg2+ in a series of biofluids. The probe is designed with a chromophore, a thiocyanate recognition unit, a π-conjugated photoelectron-transfer pathway, and a phosphonate anchor. TiO2 nanoparticles with strong affinity to phosphonate and suitable conduction band energy are used as intermediate layers to increase the Ru-1 adsorption amount and amplify the photocurrent response. Under irradiation, the Ru-1/TiO2/fluorine-doped tin oxide (FTO), with strong visible light-harvesting capacity, aqueous stability, and efficient photoelectron transfer, shows a high and stable photocurrent response. In the presence of Hg2+, however, the specific Hg2+ and NCS coordination changes the photophysical properties of Ru-1, imposing the probe with a wider band gap, a weaker absorbance, and a poorer photoelectron and hole separation efficiency, thus resulting in a significant photocurrent decrease. On the basis of the Hg2+-induced photocurrent change, the Ru-1/TiO2/FTO shows good selectivity and high sensitivity toward the PEC detection of Hg2+, with wide linear ranges from 10-12 to 10-7 and 10-7 to 10-3 g/mL, and a low limit of detection of 0.63 pg/mL. The PEC probe is recyclable and accurate for selective detection of Hg2+ in urine, serum, and cell extracts. The whole analysis can be completed within 15 min. These good analytical performances indicate that the PEC method might have great potential for the onsite detection of small molecules in biosystems.

Using Machine Learning to Aid the Interpretation of Urine Steroid Profiles.

BACKGROUND: Urine steroid profiles are used in clinical practice for the diagnosis and monitoring of disorders of steroidogenesis and adrenal pathologies. Machine learning (ML) algorithms are powerful computational tools used extensively for the recognition of patterns in large data sets. Here, we investigated the utility of various ML algorithms for the automated biochemical interpretation of urine steroid profiles to support current clinical practices. METHODS: Data from 4619 urine steroid profiles processed between June 2012 and October 2016 were retrospectively collected. Of these, 1314 profiles were used to train and test various ML classifiers' abilities to differentiate between "No significant abnormality" and "?Abnormal" profiles. Further classifiers were trained and tested for their ability to predict the specific biochemical interpretation of the profiles. RESULTS: The best performing binary classifier could predict the interpretation of No significant abnormality and ?Abnormal profiles with a mean area under the ROC curve of 0.955 (95% CI, 0.949-0.961). In addition, the best performing multiclass classifier could predict the individual abnormal profile interpretation with a mean balanced accuracy of 0.873 (0.865-0.880). CONCLUSIONS: Here we have described the application of ML algorithms to the automated interpretation of urine steroid profiles. This provides a proof-of-concept application of ML algorithms to complex clinical laboratory data that has the potential to improve laboratory efficiency in a setting of limited staff resources.

Recent advances in amino acid analysis by capillary electromigration methods: June 2015-May 2017.

In the tenth edition of this article focused on recent advances in amino acid analysis using capillary electrophoresis, we describe the most important research articles published on this topic during the period from June 2015 to May 2017. This article follows the format of the previous articles published in Electrophoresis. The new developments in amino acid analysis with CE mainly describe improvements in CE associated with mass spectrometry. Focusing on applications, we mostly describe clinical works, although metabolomics studies are also very important. Finally, works focusing on amino acids in food and agricultural applications are also described.

Advances in the analysis of "less-conventional" human body fluids: An overview of the CE- and HPLC-MS applications in the years 2015-2017.

Aim of this article is to focus the attention of the reader on the application of CE/MS and LC/MS to the analysis of human body fluids not currently used for the diagnosis of disorders and, for this reason, catalogued as "less/nonconventional" fluids, that is, tears, nasal secretions, cerumen, bronchoalveolar lavage fluid, sputum, exhaled breath condensate, nipple aspirate, breast milk, amniotic fluid, bile, seminal plasma, liposuction aspirate fluid, and synovial fluid. The pool of articles presented in this report demonstrates that, rather than being neglected, these fluids are an important resource for the evaluation of possible pathologic conditions. Thus, being a sort of mirror that reflects the normal internal characteristics and disease state of an individual, they benefit of an increasing appreciation. This review follows a previous report of this series and covers the latest developments in this field that have been published in specialist journals in the years 2015-2017.

Recent advances in CE and microchip-CE in clinical applications: 2014 to mid-2017.

CE and microchip CE (ME) are powerful tools for the analysis of a number of different analytes and have been applied to a variety of clinical fields and human samples. This review will present an overview of the most recent applications of these techniques to different areas of clinical medicine during the period of 2014 to mid-2017. CE and ME have been applied to clinical chemistry, drug detection and monitoring, hematology, infectious diseases, oncology, endocrinology, neonatology, nephrology, and genetic screening. Samples examined range from serum, plasma, and urine to lest utilized materials such as tears, cerebral spinal fluid, sweat, saliva, condensed breath, single cells, and biopsy tissue. Examples of clinical applications will be given along with the various detection systems employed.

Comparison of four methods of establishing control limits for monitoring quality controls in infectious disease serology testing.

BACKGROUND: A general trend towards conducting infectious disease serology testing in centralized laboratories means that quality control (QC) principles used for clinical chemistry testing are applied to infectious disease testing. However, no systematic assessment of methods used to establish QC limits has been applied to infectious disease serology testing. METHODS: A total of 103 QC data sets, obtained from six different infectious disease serology analytes, were parsed through standard methods for establishing statistical control limits, including guidelines from Public Health England, USA Clinical and Laboratory Standards Institute (CLSI), German Richtlinien der Bundesärztekammer (RiliBÄK) and Australian QConnect. The percentage of QC results failing each method was compared. RESULTS: The percentage of data sets having more than 20% of QC results failing Westgard rules when the first 20 results were used to calculate the mean±2 standard deviation (SD) ranged from 3 (2.9%) for R4S to 66 (64.1%) for 10X rule, whereas the percentage ranged from 0 (0%) for R4S to 32 (40.5%) for 10X when the first 100 results were used to calculate the mean±2 SD. By contrast, the percentage of data sets with >20% failing the RiliBÄK control limits was 25 (24.3%). Only two data sets (1.9%) had more than 20% of results outside the QConnect Limits. CONCLUSIONS: The rate of failure of QCs using QConnect Limits was more applicable for monitoring infectious disease serology testing compared with UK Public Health, CLSI and RiliBÄK, as the alternatives to QConnect Limits reported an unacceptably high percentage of failures across the 103 data sets.

Standardization of clinical enzyme analysis using frozen human serum pools with values assigned by the International Federation of Clinical Chemistry and Laboratory Medicine reference measurement procedures.

Variation in clinical enzyme analysis, particularly across different measuring systems and laboratories, represents a critical but long-lasting problem in diagnosis. Calibrators with traceability and commutability are imminently needed to harmonize analysis in laboratory medicine. Fresh frozen human serum pools were assigned values for alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyltransferase (GGT), creatine kinase (CK) and lactate dehydrogenase (LDH) by six laboratories with established International Federation of Clinical Chemistry and Laboratory Medicine reference measurement procedures. These serum pools were then used across 76 laboratories as a calibrator in the analysis of five enzymes. Bias and imprecision in the measurement of the five enzymes tested were significantly reduced by using the value-assigned serum in analytical systems with open and single-point calibration. The median (interquartile range) of the relative biases of ALT, AST, GGT, CK and LDH were 2.0% (0.6-3.4%), 0.8% (-0.8-2.3%), 1.0% (-0.5-2.0%), 0.2% (-0.3-1.0%) and 0.2% (-0.9-1.1%), respectively. Before calibration, the interlaboratory coefficients of variation (CVs) in the analysis of patient serum samples were 8.0-8.2%, 7.3-8.5%, 8.1-8.7%, 5.1-5.9% and 5.8-6.4% for ALT, AST, GGT, CK and LDH, respectively; after calibration, the CVs decreased to 2.7-3.3%, 3.0-3.6%, 1.6-2.1%, 1.8-1.9% and 3.3-3.5%, respectively. The results suggest that the use of fresh frozen serum pools significantly improved the comparability of test results in analytical systems with open and single-point calibration.

High-throughput analysis of sulfatides in cerebrospinal fluid using automated extraction and UPLC-MS/MS.

Sulfatides (STs) are a group of glycosphingolipids that are highly expressed in brain. Due to their importance for normal brain function and their potential involvement in neurological diseases, development of accurate and sensitive methods for their determination is needed. Here we describe a high-throughput oriented and quantitative method for the determination of STs in cerebrospinal fluid (CSF). The STs were extracted using a fully automated liquid/liquid extraction method and quantified using ultra-performance liquid chromatography coupled to tandem mass spectrometry. With the high sensitivity of the developed method, quantification of 20 ST species from only 100 µl of CSF was performed. Validation of the method showed that the STs were extracted with high recovery (90%) and could be determined with low inter- and intra-day variation. Our method was applied to a patient cohort of subjects with an Alzheimer's disease biomarker profile. Although the total ST levels were unaltered compared with an age-matched control group, we show that the ratio of hydroxylated/nonhydroxylated STs was increased in the patient cohort. In conclusion, we believe that the fast, sensitive, and accurate method described in this study is a powerful new tool for the determination of STs in clinical as well as preclinical settings.

Urine and oral fluid drug testing in support of pain management.

In recent years, the abuse of opioid drugs has resulted in greater prevalence of addiction, overdose, and deaths attributable to opioid abuse. The epidemic of opioid abuse has prompted professional and government agencies to issue practice guidelines for prescribing opioids to manage chronic pain. An important tool available to providers is the drug test for use in the initial assessment of patients for possible opioid therapy, subsequent monitoring of compliance, and documentation of suspected aberrant drug behaviors. This review discusses the issues that most affect the clinical utility of drug testing in chronic pain management with opioid therapy. It focuses on the two most commonly used specimen matrices in drug testing: urine and oral fluid. The advantages and disadvantages of urine and oral fluid in the entire testing process, from specimen collection and analytical methodologies to result interpretation are reviewed. The analytical sensitivity and specificity limitations of immunoassays used for testing are examined in detail to draw attention to how these shortcomings can affect result interpretation and influence clinical decision-making in pain management. The need for specific identification and quantitative measurement of the drugs and metabolites present to investigate suspected aberrant drug behavior or unexpected positive results is analyzed. Also presented are recent developments in optimization of test menus and testing strategies, such as the modification of the standard screen and reflexed-confirmation testing model by eliminating some of the initial immunoassay-based tests and proceeding directly to definitive testing by mass spectrometry assays.

Validation of two point-of-care tests against standard lab measures of NO in saliva and in serum.

Nitric oxide (NO) is an endogenous signaling molecule, which plays important roles in cardiometabolic health. A significant source of NO is dietary nitrate (NO3), which is initially metabolized by oral bacteria into nitrite (NO2-) and is subsequently converted into NO once digested in the acidic gastric environment. Inexpensive non-invasive tests for measuring nitrite from saliva have been developed as a means for individuals to monitor their NO bioavailability. However, few studies exist in the literature validating and comparing these products with standard lab assays. The objective of this study was to validate two commonly used commercial strips: Nitric Oxide Test Strips (Berkeley Test) and Nitric Oxide Indicator Strips (Neogenesis) against standard lab measures for saliva and serum nitrite/nitrate. A stratified random sample of 20 non-smoking, overweight or obese participants between 40 to 65 years of age, were selected for this study from the baseline data of the San Juan Overweight Adults Longitudinal Study (SOALS). There was a significant correlation between the measures from the two nitrite-detecting-strips after controlling for the stratification variables (metabolic syndrome, and mouthwash use) (r = 0.75). Measurements from both strips correlated significantly with salivary nitrite levels (r = 0.76 for Berkeley strips; r = 0.59 for Neogenesis). Neither of the strips had a significant correlation with the levels of saliva nitrate, serum nitrite and serum nitrate. In conclusion, commercially available Berkeley and Neogenesis strips provide a reasonable surrogate for salivary, but not for systemic nitrite levels.