Do capillary dried blood spot concentrations of gamma-hydroxybutyric acid mirror those in venous blood? A comparative study.

Gamma-hydroxybutyric acid (GHB) is a well-known illicit club and date-rape drug. Dried blood spot (DBS) sampling is a promising alternative for classical venous sampling in cases of (suspected) GHB intoxication since it allows rapid sampling, which is of interest for the extensively metabolized GHB. However, there is limited data if -and how- capillary DBS concentrations correlate with venous concentrations. We conducted a comparative study in 50 patients with suspected GHB intoxication, to determine and to correlate GHB concentrations in venous DBS (vDBS) and capillary DBS (cDBS). This is the first study that evaluates in a large cohort the correlation between capillary and venous concentrations of an illicit drug in real-life samples. Of the 50 paired samples, 7 were excluded: the vDBS concentration was below the LLOQ of 2 µg/mL in 3 cases and 4 samples were excluded after visual inspection of the DBS. Bland-Altman analysis revealed a mean % difference of -2.8% between cDBS and vDBS concentrations, with the zero value included in the 95% confidence interval of the mean difference in GHB concentration. A paired sample t-test confirmed this observation (p = 0.17). Also the requirement for incurred sample reproducibility was fulfilled: for more than two-thirds of the samples the concentrations obtained in cDBS and those in vDBS were within 20% of their mean. Since equivalent concentrations were observed in cDBS and vDBS, blood obtained by fingerprick can be considered a valid alternative for venous blood for GHB determination.

Screening and confirmation methods for GHB determination in biological fluids.

The purpose of this review is to provide a comprehensive overview of reported methods for screening and confirmation of the low-molecular-weight compound and drug of abuse gamma-hydroxybutyric acid (GHB) in biological fluids. The polarity of the compound, its endogenous presence, its rapid metabolism after ingestion, and its instability during storage (de novo formation and interconversion between GHB and its lactone form gamma-butyrolactone) are challenges for the analyst and for interpretation of a positive result. First, possible screening procedures for GHB are discussed, including colorimetric, enzymatic, and chromatography-based procedures. Confirmation methods for clinical and forensic cases mostly involve gas chromatography (coupled to mass spectrometry), although liquid chromatography and capillary zone electrophoresis have also been used. Before injection, sample-preparation techniques include (a combination of) liquid-liquid, solid-phase, or headspace extraction, and chemical modification of the polar compound. Also simple "dilute-and-shoot" may be sufficient for urine or serum. Advantages, limitations, and trends are discussed.

Determination of gamma-hydroxybutyric acid in biofluids using a one-step procedure with "in-vial" derivatization and headspace-trap gas chromatography-mass spectrometry.

A headspace-trap gas chromatography-mass spectrometry (HS-trap GC-MS) method was developed to determine GHB, a low molecular weight compound and drug of abuse, in various biological fluids. Combining this relatively novel and fully automated headspace technique with "in-vial" methylation of GHB allowed for a straightforward approach. One single method could be used for all biofluids (urine, plasma, serum, whole blood or lyzed blood), requiring only 100µl of sample. Moreover, our approach involves mere addition of all reagents and sample into one vial. Following optimization of headspace conditions and trap settings, validation was performed. Although sample preparation only consists of the addition of salt and derivatization reagents directly to a 100µl-sample in a HS-vial, adequate method sensitivity and selectivity was obtained. Calibration curves ranged from 5 to 150µg/ml GHB for urine, from 2 to 150µg/ml for plasma, and from 3.5 to 200µg/ml for whole blood. Acceptable precision and accuracy (<13% bias and imprecision) were seen for all quality controls (QC's) (LLOQ-level, low, medium, high), including for the supplementary serum- and lyzed blood-based QC's, using calibration curves prepared in plasma or whole blood, respectively. Incurred sample reanalysis demonstrated assay reproducibility, while cross-validation with another GC-MS method demonstrated that our method is a valuable alternative for GHB determination in toxicological samples, with the advantage of requiring only 100µl and minimal hands-on time, as sample preparation is easy and injection automated.

Feasibility of following up gamma-hydroxybutyric acid concentrations in sodium oxybate (Xyrem®)-treated narcoleptic patients using dried blood spot sampling at home: an exploratory study.

BACKGROUND: Gamma-hydroxybutyric acid (GHB), well known as a party drug, especially in Europe, is also legally used (sodium oxybate, Xyrem(®)) to treat a rare sleep disorder, narcolepsy with cataplexy. This exploratory study was set up to measure GHB concentrations in dried blood spots (DBS) collected by narcoleptic patients treated with sodium oxybate. Intra- and inter-individual variation in clinical effects following sodium oxybate administration has been reported. The use of DBS as a sampling technique, which is stated to be easy and convenient, may provide a better insight into GHB concentrations following sodium oxybate intake in a real-life setting. OBJECTIVE: The aim was twofold: evaluation of the applicability of a recently developed DBS-based gas chromatography-mass spectrometry (GC-MS) method, and of the feasibility of the sampling technique in an ambulant setting. METHODS: Seven narcoleptic patients being treated with sodium oxybate at the Department for Respiratory Diseases of Ghent University Hospital were asked to collect DBS approximately 20 min after the first sodium oxybate (Xyrem(®); UCB Pharma Ltd, Brussels, Belgium) intake on a maximum of 7 consecutive days. Using an automatic lancet, patients pricked their fingertip and, after wiping off the first drop of blood, subsequent drops were collected on a DBS card. The DBS cards were sent to the laboratory by regular mail and, before analysis, were visually inspected to record DBS quality (large enough, symmetrically spread on the filter paper with even colouration on both sides of the filter paper). RESULTS: Of the seven patients, three patients succeeded to collect five series of DBS, one patient decided to cease participation because of nausea, one was lost during follow-up and two patients started falling asleep almost immediately after the intake of sodium oxybate. Analysing the DBS in duplicate resulted in acceptable within-DBS card precision. DBS with acceptable quality were obtained by patients without supervision. CONCLUSION: Our results demonstrate the acceptable precision of the complete procedure, from sampling at home to quantitative analysis in the laboratory. Given the intra- and inter-individual variability in clinical effects seen with sodium oxybate, the easy adaptation of DBS sampling opens the possibility of following up GHB concentrations in patients in real-life settings in future studies.

Dried blood spots in toxicology: from the cradle to the grave?

About a century after its first described application by Ivar Bang, the potential of sampling via dried blood spots (DBS) as an alternative for classical venous blood sampling is increasingly recognized. Perhaps best known is the use of DBS in newborn screening programs, ignited by the hallmark paper by Guthrie and Susi half a century ago. However, it is only recently that both academia and industry have recognized the many advantages that DBS sampling may offer for bioanalytical purposes, as reflected by the strong increase in published reports during the last few years. Currently, major DBS applications include newborn screening for metabolic disorders, epidemiological surveys (e.g. HIV monitoring), therapeutic drug monitoring (TDM), as well as toxicology. In this review, we provide a comprehensive overview of the distinct subdisciplines of toxicology for which DBS sampling has been applied. DBS sampling for toxicological evaluation has been performed from birth until autopsy, aiming at the assessment of therapeutic drugs, drugs of abuse, environmental contaminants, toxins, as well as (trace) elements, with applications situated in fields as toxicokinetics, epidemiology and environmental and forensic toxicology. We discuss the strengths and limitations of DBS in the different subdisciplines and provide future prospects for the use of this promising sampling technique in toxicology.

Determination of gamma-hydroxybutyric acid in dried blood spots using a simple GC-MS method with direct "on spot" derivatization.

The objective of this study was the development of an accurate and sensitive method for the determination of gamma-hydroxybutyric acid (GHB) in dried whole blood samples using a GC-MS method. The complete procedure was optimized, with special attention on the sample pretreatment, and validated. Therefore, dried blood spots of only 50 µl were prepared and, after the addition of internal standard GHB-d6, directly derivatized using 100 µl of a freshly prepared mixture of trifluoroacetic acid anhydride and heptafluorobutanol (2:1). The derivatized extract was injected into a gas chromatograph coupled to a mass spectrometer (GC-MS), operating in the electron impact mode, with a total run time of 12.3 min. Method validation included the evaluation of linearity, precision, accuracy, sensitivity, selectivity, and stability. A weighting factor of 1/x(2) was chosen and acceptable intra-batch precision, inter-batch precision, and accuracy were seen. The linear calibration curve ranged from 2 to 100 µg/ml, with a limit of detection of 1 µg/ml. Our procedure, utilizing the novel approach of direct "on spot" derivatization followed by analysis with GC-MS, proved to be reliable, fast, and applicable in routine toxicology.