Читать книгу Fundamentals of Analytical Toxicology - Robin Whelpton - Страница 52

If poisoning is suspected, a 10 mL blood sample (lithium heparin or EDTA tube) should be taken from an adult (proportionally less from a young child) as soon as possible. In addition, 2 mL of blood should be collected in a fluoride/oxalate tube if ethanol is suspected. Note that tubes of this type for clinical use contain only ca. 0.1 % w/v fluoride (Table 2.3), whereas ca. 2 % w/v fluoride (40 mg sodium fluoride per 2 mL blood) is needed to inhibit fully microbial action in such specimens. Addition of fluoride may also help protect other labile drugs such as clonazepam, cocaine, and nitrazepam from degradation. If possible, the retention of an unpreserved blood sample is also advisable.

Table 2.4 Sample requirements: general analytical toxicology

Sample	Notesa
Whole blood	10 mL (lithium heparin or EDTA tube – use fluoride/oxalate if ethanol suspected; plastic tube if paraquat suspected; glass or plastic tube with minimal headspace if carbon monoxide or other volatiles suspected)
or Plasma/serum	5 mL (send whole blood if volatiles, metals, and some other compounds suspected – see above)
Urineb	20–50 mL (plain bottle, no preservativec)
Gastric contentsd	25–50 mL (plain bottle, no preservative)
Scene residuese	As appropriate

^aSmaller volumes may often be acceptable, for example in the case of young children

^bNormally the only sample that is required for substance misuse screening

^cSodium fluoride (2 % w/v) should be added if ethanol is suspected and blood is not available

^dIncludes vomit, gastric lavage (SWO, first sample), etc.

^eTablet bottles, drinks containers, aerosol canisters, etc. – pack entirely separately from biological samples, especially if poisoning with volatiles is a possibility

Collection of urine, stomach contents, and ‘scene residues’, i.e. material such as tablet bottles or drinks containers found at the scene of an incident may be helpful (Table 2.4). Samples of other appropriate fluids and tissues should also be collected as detailed below, especially when investigating deaths (Table 2.5), but may not be required for analysis unless either special investigations are required or decomposition is advanced (Dinis-Oliveira et al., 2010; Dinis-Oliveira et al., 2017; Belsey & Flanagan, 2016). However, such samples should be retained (2–8 or –20 °C) in case they are needed. The advantages and disadvantages of various specimens are detailed in Table 2.6. There are special considerations in sample collection and storage for metals/trace elements analysis (Section 21.2).

Information recorded on the sample container at the time the sample is collected should include the name of the patient (first and family or last name) and date of birth, patient/subject/animal number, the date and time of collection, and the sample type. Many laboratories will have a bespoke analysis request form to accompany the sample(s) on which this and any other appropriate information such as a note of any preservative added to the sample, site of collection of blood, etc. should be recorded (Box 2.2). The date and time of receipt of all specimens by the laboratory should be recorded and a unique identifying number assigned in each case.

Table 2.5 Sample requirements: post-mortem biochemistry and toxicology

Sample	Notesa
Heart whole blood (right ventricle)	20 mL unpreserved (normally qualitative toxicology only)
Jugular vein whole blood	20 mL unpreserved (normally qualitative toxicology only)
Peripheral whole blood	20 mL from femoral or other peripheral site ensuring no contamination from urine or from central or cavity blood. Collect one portion into 2 % w/v sodium fluoride and another into a plain tube
Urine	20–50 mL if available (plain tube, no preservative unless a portion is required for ethanol measurement)
Gastric contentsb	25–50 mL (plain bottle, no preservative; record the total weight or volume)
Vitreous humour	Maximum available, plain tube, separate specimens from each eye if feasible. Avoid excessive suction to minimize the risk of aspirating retinal fragments. Collect one portion into 2 % w/v sodium fluoride if for ethanol measurement
Cerebrospinal fluid	5–10 mL, plain tube
Pericardial fluid	Maximum available, plain tube
Synovial fluidc	Maximum available, plain tube
Intra-osseous fluid	Maximum available, plain tube
Bile	Maximum available, plain tube
Liver and other tissues	Liver 10 g (deep inside right lobe), other tissues 10 g as appropriated
Scene residuese	As appropriate

^aSmaller volumes may often be acceptable, for example in the case of young children

^bIncludes vomit, gastric lavage (SWO, first sample), etc.

^cAlternative if vitreous humour not available

^dBecause there is little information on drug distribution within solid tissues in man, collection of approximately 10 g specimens from several sites from organs such as the brain is recommended if the whole organ is available

^eTablet bottles, drink containers, aerosol canisters, etc. should be packed entirely separately from biological samples, especially if poisoning with volatiles is a possibility

Table 2.6 Advantages and disadvantages of different sample types in analytical toxicology

Specimen	Advantage	Disadvantage	Comment
Blood (plasma/serum or whole blood)	Detect parent compound. Interpretation of quantitative data	Limited volume. Low concentrations of many basic drugs and some other poisons	Interpretation of quantitative results from post-mortem blood may be difficult
Dried blood spot on filter paper	If known volume of venous blood added, then easy to store and transport (room temperature)	Almost impossible to get accurate volume of blood without use of a pipette or special device. Need analyte to be stable on the paper	Advocated for collecting capillary blood, but capillary blood not venous blood
Urine	Often large volume.High concentrations of many poisons, but sometimes only metabolites detectable	Not always available. Quantitative data not often useful	Standard sample for substance misuse screening
Gastric aspirate (stomach contents, SWO, vomit, etc.)	May contain large amounts of poison, particularly if ingested	If available, variable sample. Limited use if exposure is by inhalation or injection	Ensure no cross-contamination of other specimens during transport/storage/analysis
Oral fluid	Non-invasive. Qualitative information on exposure to many drugs	Variable sample hence little use for quantitative work. Low concentrations of many analytes	Interpretation of quantitative results may be difficult
Hair/nails or nail clippings	Usually available even if decomposition advanced	High sensitivity needed. May only give exposure data for the weeks/months before death. Susceptible to external contamination	Easy to store (room temperature)
Exhaled air	Non-invasive. Large volume available	Need live patient. Analyte must be volatile or present as an aerosol	Mainly used to assess ethanol ingestion, carbon monoxide exposure, and monitor volatile anaesthetics
Scene residues (tablet bottles, aerosol cans, etc. near patient)	May contain large amounts of poison	May not have been the poison taken	Ensure no cross-contamination of other specimens during transport/storage/analysis
Vitreous humour	May be used instead of urine if latter not available	Limited volume but normally two specimens	Analysis may be valuable to help interpret post-mortem blood data for ethanol and for some other compounds
Additional tissues (liver, brain, lung, kidney, etc.)	May contain large amounts of poison.If available then large quantity	Interference in analysis.Difficult to prepare calibrators/QCs, assess recovery, etc. Quantitative data not always easy to interpret	Analysis may be valuable to help interpret post-mortem blood data