Quantitation of phosphatidylethanol in dried blood after volumetric absorptive microsampling

Interlaboratory comparison of phosphatidylethanol in dried blood spots using different sampling devices

Phosphatidylethanol (PEth) has become an important marker to assess drinking behaviour and monitor abstinence. Despite its increasing use, knowledge on robustness and standardization and comparability of methods and results are still limited. In 2022, the first international consensus for the use of PEth and its interpretation was published. To establish an experience-based foundation for further harmonization, three rounds of interlaboratory comparison using microsamples were conducted. Participating laboratories sent their sampling devices to the laboratory of Forensic Toxicology at the University of Bern, where for each round, four different authentic blood samples were applied to the devices and sent back. The PEth 16:0/18:1 target concentrations covered a range between 16 and 474 ng/mL (0.023 and 0.676 μmol/L, respectively) and included sample concentrations close to the decision limits of 20 and 200 ng/mL (0.025 and 0.28 μmol/L, respectively). Evaluation of the results based on guidelines by Horwitz and the Society of Toxicological and Forensic Chemistry (GTFCh) showed that 73% of all participating laboratories quantified and reported all samples (N = 4 for each round) within the acceptable limits. More than 90% quantified and reported at least one sample within the acceptable limits.

The complementarity of phosphatidylethanol in whole blood and ethyl glucuronide in hair as biomarkers for the monitoring of alcohol use

Monitoring long-term alcohol use and/or abstinence is essential in clinical and medico-legal cases. Analysis of ethyl glucuronide (EtG) in hair provides information on alcohol consumption over several months. However, there is a lag time between ethanol consumption, incorporation of EtG in the hair bulb and hair growing out of the scalp. Phosphatidylethanol (PEth) 16:0/18:1 analysis in whole blood has a detection window of 2-4 weeks, allowing for the detection of recent alcohol consumption. In this study, 2340 paired samples (of hair and venous whole blood from 1170 individuals) were analysed for EtG in hair (hEtG) and PEth 16:0/18:1 in venous whole blood. PEth 16:0/18:1 and hEtG results were subdivided into three categories according to the consensus of SoHT (hEtG) and PEth-NET (PEth): abstinence/low, moderate or excessive alcohol consumption. For hEtG analysis, 446 individuals presented abstinence/low alcohol consumption, of which 2% were classified as excessive alcohol users through PEth 16:0/18:1 analysis. This suggests excessive alcohol consumption in the weeks before sample collection. Out of 483 individuals classified as heavy alcohol users based on hEtG analysis, 14% showed abstinence/low alcohol consumption for PEth 16:0/18:1 analysis, implying that these subjects stopped drinking 2-4 weeks before sample collection. Our results show that the analysis of the two different biomarkers can lead to a more accurate categorisation of individuals. Therefore, we emphasize that for the retrospective investigation of alcohol use, it is necessary to include two alcohol use biomarkers with different detection windows.

LC-MS/MS analysis of erythrocyte phosphatidylethanol in haematocrit-corrected whole blood versus isolated erythrocytes: Results of an inter-laboratory comparison

Phosphatidylethanol (PEth) is a non-oxidative metabolite of alcohol (ethanol), which is a sensitive and specific indicator of historic ethanol consumption. Although PEth production from ethanol is catalysed by the ubiquitous enzyme phospholipase D, it resides mainly within the erythrocyte compartment of the blood. PEth analysis has been reported in different preparations of whole blood, representing one of the barriers of inter-laboratory comparisons. We previously reported that expressing PEth concentrations in terms of blood erythrocyte content is more sensitive than whole blood volume, and haematocrit-corrected liquid whole blood calculations of erythrocyte PEth and isolated erythrocyte PEth concentrations are comparable when assayed under identical analytical conditions. Acceptance of a clinical diagnostic assay by accreditation bodies requires proficiency testing with a third-party analytical facility. To explore different blood preparations within the same inter-laboratory program, 60 matched isolated erythrocyte or liquid whole blood specimens were tested at three laboratories. Laboratories measured PEth by liquid chromatography-tandem mass spectrometry (LC-MS/MS), two using isolated erythrocytes, while the third used liquid whole blood, which underwent haematocrit correction before comparison with isolated erythrocyte PEth concentrations. There was acceptable consensus (87%) among laboratories to detect PEth around a cut-off of 35 μg/L of erythrocytes. Each laboratory correlated well with the group average PEth concentration (R > 0.98) for each specimen above the cut-off. Differences were observed between laboratories in bias, which did not affect comparable sensitivity at the selected cut-off. This work demonstrates the feasibility of an inter-laboratory comparison for erythrocyte PEth analysis across different LC-MS/MS methodologies and different blood preparations.

Volumetric Absorptive Microsampling in the Analysis of Endogenous Metabolites

Volumetric absorptive microsampling (VAMS) has arisen as a relevant tool in biological analysis, offering simplified sampling procedures and enhanced stability. Most of the attention VAMS has received in the past decade has been from pharmaceutical research, with most of the published work employing VAMS targeting drugs or other exogenous compounds, such as toxins and pollutants. However, biomarker analysis by employing blood microsampling has high promise. Herein, a comprehensive review on the applicability of VAMS devices for the analysis of endogenous metabolites/biomarkers was performed. The study presents a full overview of the analysis process, incorporating all the steps in sample treatment and validation parameters. Overall, VAMS devices have proven to be reliable tools for the analysis of endogenous analytes with biological importance, often offering improved analyte stability in comparison with blood under ambient conditions as well as a convenient and straightforward sample acquisition model.

Biomarkers of moderate alcohol intake and alcoholic beverages: a systematic literature review

The predominant source of alcohol in the diet is alcoholic beverages, including beer, wine, spirits and liquors, sweet wine, and ciders. Self-reported alcohol intakes are likely to be influenced by measurement error, thus affecting the accuracy and precision of currently established epidemiological associations between alcohol itself, alcoholic beverage consumption, and health or disease. Therefore, a more objective assessment of alcohol intake would be very valuable, which may be established through biomarkers of food intake (BFIs). Several direct and indirect alcohol intake biomarkers have been proposed in forensic and clinical contexts to assess recent or longer-term intakes. Protocols for performing systematic reviews in this field, as well as for assessing the validity of candidate BFIs, have been developed within the Food Biomarker Alliance (FoodBAll) project. The aim of this systematic review is to list and validate biomarkers of ethanol intake per se excluding markers of abuse, but including biomarkers related to common categories of alcoholic beverages. Validation of the proposed candidate biomarker(s) for alcohol itself and for each alcoholic beverage was done according to the published guideline for biomarker reviews. In conclusion, common biomarkers of alcohol intake, e.g., as ethyl glucuronide, ethyl sulfate, fatty acid ethyl esters, and phosphatidyl ethanol, show considerable inter-individual response, especially at low to moderate intakes, and need further development and improved validation, while BFIs for beer and wine are highly promising and may help in more accurate intake assessments for these specific beverages.

Development and Validation of Seven Phosphatidylethanol Homologues in Dried Blood Spots Including Preliminary Results after Excessive Use of an Ethanol-Based Hand Sanitizer

Phosphatidylethanol (PEth) has become a widespread marker offering an up to 4-week retrospective window to detect alcohol use. Due to the pandemic of coronavirus disease 2019, ethanol-based hand sanitizers are frequently used. The aim of this study was to develop and validate a method for the determination of up to seven different homologues of PEth from dried blood spots (DBSs) after use of an ethanol-based hand sanitizer. The objectives of its preliminary application were to prove whether a threshold of 20 ng/mL for PEth 16:0/18:1 is reached and whether other homologues are formed as well as if positive findings of urinary ethyl glucuronide (UEtG) can be observed with respect to assess monitoring of abstinence control programs. Ten volunteers (8 occasional and 2 regular drinkers) were recruited to excessively use an ethanol-based hand sanitizer on 5 successive days. DBSs and urine samples were collected daily. PEth and UEtG were determined by liquid chromatography--tandem mass spectrometry. In total, two volunteers with initial PEth 16:0/18:1 concentrations of 19.3 and 14.6 ng/mL exceeded the threshold of 20 ng/mL six times. Subjects drinking daily or almost daily had starting PEth 16:0/18:1 concentrations of 242 and 354 ng/mL, showing a decline of PEth concentrations in six out of the seven homologues over 5 days. In teetotalers, formation of PEth species could not be observed. Thus, not satisfying requirements in an alcohol monitoring program with initial PEth-negative blood cannot be explained by a frequent use of ethanol-based hand sanitizer only. In cases of regular alcohol consumption, PEth homologues are not likely to be further influenced. However, results indicated that individuals with a PEth concentration close to 20 ng/mL are at risk of exceeding the threshold by using ethanol-based hand sanitizer.

Applications of Volumetric Absorptive Microsampling Technique: A Systematic Critical Review

METHODS

A novel microsampling device called Volumetric Absorptive microsampling (VAMS), developed in 2014, appears to have resolved the sample inhomogeneity inherent to dried blood spots, with improved precision in the volume of sample collected for measuring drug concentration. A literature search was conducted to identify several analytical and pharmacokinetic studies that have used VAMS in recent years.

RESULTS

The key factors for proper experimental design and optimization of the extraction of drugs and metabolites of interest from the device were summarized. This review focuses on VAMS and elaborates on bioanalytical factors, method validation steps, and scope of this technique in clinical practice.

CONCLUSIONS

The promising microsampling method VAMS is especially suited for conducting pharmacokinetic studies with very small volumes of blood, especially in special patient populations. Clinical validation of every VAMS assay must be conducted prior to the routine practical implementation of this method.

Microsampling tools for collecting, processing, and storing blood at the point-of-care

In the wake of the COVID-19 global pandemic, self-administered microsampling tools have reemerged as an effective means to maintain routine healthcare assessments without inundating hospitals or clinics. Finger-stick collection of blood is easily performed at home, in the workplace, or at the point-of-care, obviating the need for a trained phlebotomist. While the initial collection of blood is facile, the diagnostic or clinical utility of the sample is dependent on how the sample is processed and stored prior to transport to an analytical laboratory. The past decade has seen incredible innovation for the development of new materials and technologies to collect low-volume samples of blood with excellent precision that operate independently of the hematocrit effect. The final application of that blood (i.e., the test to be performed) ultimately dictates the collection and storage approach as certain materials or chemical reagents can render a sample diagnostically useless. Consequently, there is not a single microsampling tool that is capable of addressing every clinical need at this time. In this review, we highlight technologies designed for patient-centric microsampling blood at the point-of-care and discuss their utility for quantitative sampling as a function of collection material and technique. In addition to surveying methods for collecting and storing whole blood, we emphasize the need for direct separation of the cellular and liquid components of blood to produce cell-free plasma to expand clinical utility. Integrating advanced functionality while maintaining simple user operation presents a viable means of revolutionizing self-administered microsampling, establishing new avenues for innovation in materials science, and expanding access to healthcare.

Set-up of a population-based model to verify alcohol abstinence via monitoring of the direct alcohol marker phosphatidylethanol 16:0/18:1

BACKGROUND AND AIMS

Phosphatidylethanol 16:0/18:1 (PEth) is a biomarker for alcohol intake. It has a half-life of 7.9 days. Chronic alcohol consumption causes high PEth values. It can take weeks before PEth values fall below the decision limit for 'alcohol abstinence'. Our aim was to validate whether alcohol abstinence can be determined based on two consecutive PEth results above the decision limit.

DESIGN

Observational study.

SETTING

Belgium, February 2019. The study was linked to a social initiative in Belgium, 'Tournée Minérale'.

PARTICIPANTS

Adults (aged > 18 years, n = 796) with varying drinking habits who self-reportedly refrained from alcohol consumption during the study.

MEASUREMENTS

A validated liquid chromatography-tandem mass spectrometry method was used to quantify PEth in participants' dried blood samples, collected at three time-points via remote fingerprick-based self-sampling.

FINDINGS

A population-based algorithm to evaluate abstinence based on 95% prediction limits was developed by fitting a linear mixed-effect model to discern patterns in PEth elimination over time. It took intra- and inter-individual variability into consideration. The algorithm was included in a two-step decision tree, assessing whether (i) PEth values fell within the prediction interval and (ii) the slope between two PEth values was consistent with no alcohol consumption. Data for 74 participants reporting no alcohol intake during the study were used for validation. With a detection limit of 'four units spread over 14 days', the sensitivity and specificity of the decision tree was 89%.

CONCLUSIONS

Claims of alcohol abstinence can be verified using a two-step decision tree for phosphatidylethanol 16:0/18:1 values, even when those values are above the limit for 'alcohol abstinence'.

Comparison of automated determination of phosphatidylethanol (PEth) in dried blood spots (DBS) with previous manual processing and testing

Phosphatidylethanol (PEth) is a sensitive and specific biomarker of alcohol consumption in the prior 2-3 weeks. Standard, manual PEth testing using dried blood spots (DBS) is a multi-step time-consuming process. A novel, automated processing and testing method has been developed to decrease DBS processing and testing time. We conducted automated testing, using regioisomerically pure PEth reference material, on randomly selected DBS, which had previously been tested via manual methods and then stored for 3-6 years at -80 °C, to compare the results (PEth 16:0/18:1 homologue). We chose samples for re-testing using categories found in the literature as follows: 1) PEth <20 ng/mL; 2) PEth 20-200 ng/mL; 3) PEth >200-1000 ng/mL; 4) PEth >1000 ng/mL. We calculated agreement between the categories using the weighted kappa statistic (n = 49 DBS). We quantified agreement between continuous measures using the intraclass correlation coefficient (ICC), and further described the relationship between variables using Spearman correlation. The median PEth result was 155 ng/mL (interquartile range [IQR]: 1-1312 ng/mL) via automated methods and 98.8 ng/mL (IQR: 10.2-625.0 ng/mL) via manual methods. The weighted kappa comparing the automated to manual PEth results was 0.76 [95% Confidence Interval (CI): 0.66-0.86]. The ICC was 0.69 (95% CI: 0.54-0.79), and the Spearman correlation was 0.98 (95% CI: 0.95-0.99). While the new methods yielded somewhat higher PEth values, we found good to excellent agreement between clinically relevant PEth categories. Automated DBS processing and testing using new reference standards are promising methods for PEth testing.

Measurement of the alcohol biomarker phosphatidylethanol (PEth) in dried blood spots and venous blood-importance of inhibition of post-sampling formation from ethanol

Phosphatidylethanol (PEth) is a group of phospholipids formed in cell membranes following alcohol consumption by action of the enzyme phospholipase D (PLD). PEth measurement in whole blood samples is established as a specific alcohol biomarker with clinical and forensic applications. However, in blood specimens containing ethanol, formation of PEth may continue after sampling leading to falsely elevated concentrations. This study evaluated the use of dried blood spot (DBS) and microsampling specimens to avoid post-sampling formation of PEth. Filter paper cards and three commercial devices for volumetric microsampling of finger-pricked blood were assessed, using PEth-negative and PEth-positive whole blood fortified with 2 g/L ethanol. PEth (16:0/18:1) was measured by LC–MS/MS. Post-sampling formation of PEth occurred in wet blood and in the volumetric devices, but not filter paper cards, when stored at room temperature for 48 h. Addition of an inhibitor of PLD, sodium metavanadate (NaVO₃), eliminated post-sampling formation during storage and drying. In conclusion, the present study confirmed previous observations that PEth can be formed in blood samples after collection, if the specimen contains ethanol. The results further demonstrated that post-sampling formation of PEth from ethanol also occurred with commercial devices for volumetric dried blood microsampling. In order for a PEth result not to be questioned, it is recommended to use a PLD inhibitor, whether venous blood is collected in a vacutainer tube or finger-pricked blood is obtained using devices for dried blood microsampling.