Toxicology: analysis for drugs (FSR-GUI-0029) (accessible)

Question 1

Introduction

Accepted Answer

1.1. Background

1.1.1. Section 5A (s5A) of the Road Traffic Act 1988 ^{[footnote 1]} was implemented in March 2015 and corresponding The Drug Driving (Specified Limits) (England and Wales) Regulations, introduced statutory blood concentration limits for a panel of sixteen controlled drugs. In April 2015, the regulations were subsequently amended to include amphetamine, expanding the panel to seventeen drugs.

1.1.2. In 2021, the Forensic Science Regulator (FSR) published issue 5 of FSR-C-133 ‘The Analysis and Reporting of Whole Blood Specimens in Relation to s5A Road Traffic Act 1988 (Drug Driving)’, establishing regulatory requirements for s5A analysis. In October 2023 FSR-C-133 was incorporated into the FSR’s statutory Code of Practice (Version 1) ^{[footnote 2]}, designated as Forensic Science Activity (FSA) DTN-102.

1.1.3. In 2023 the FSR created the Section 5A Toxicology Working Group, bringing together representatives from across the community, and tasked it with reviewing the DTN-102 FSA-specific requirements for the FSR’s Code of Practice (Version 2) ^{[footnote 3]} due to significant quality failures in the undertaking of drug driving analysis. Version 2 of the Code came into force on 2nd October with a delayed compliance requirement for the DTN-102 specific requirements, which came into force on 2nd April 2026. This document is the product of Phase 2 of the Working Group, providing guidance to address remaining scientific challenges in s5A toxicology analysis.

1.2. Scope

1.2.1. This guidance document sets out the principles that should be followed by any forensic unit undertaking FSA – DTN 102 – Toxicology: analysis for drugs in relation to s5A of the Road Traffic Act 1988. This document does not apply to toxicology analysis under any other FSAs.

1.2.2. The guidance provides additional detail to the DTN-102 FSA-specific requirements stipulated in the FSR’s Code of Practice (Version 2, Section 94) ^{[footnote 3]}.

1.2.3. Forensic units are advised to adhere to the guidance, as the document aims to address potential risk areas. However, non-compliance with the guidance does not, by itself, establish non-compliance with the Code. Declarations to guidance documents on reports generated by the forensic unit are not compulsory.

1.2.4. It is acknowledged that forensic units may need to implement procedural changes to comply with the guidance. Therefore, it is not expected that forensic units will be able to adhere to all areas of the guidance immediately at the time of publishing, but instead may be achieved incrementally.

Question 2

Sample quality

Accepted Answer

2.1. Sample storage

2.1.1. Blood samples should be stored refrigerated prior to analysis. The freezing of blood samples has the potential to impact the stability of drug concentrations and if the vial is full there is a risk of breakage. Therefore, blood samples should not be frozen prior to analysis.

2.1.2. Forensic service providers (FSPs) undertaking DTN-102 should advise their customers of correct sample storage practices.

2.2. Clotted blood samples

2.2.1. FSPs should have a policy for managing clotted s5A blood samples which should include the below points.

a. Blood samples should be thoroughly vortex-mixed prior to analysis.

b. Where a clot is suspected to be present, a critical finding check should be conducted by another trained analyst to confirm.

c. Any blood sample confirmed as clotted should be rejected for s5A analysis.

d. There should be a clear mechanism by which the presence of a clot is recorded in the laboratory’s case management system.

e. There should be a clear procedure outlining next steps upon confirmation of a clotted sample (e.g., escalation to seniors, informing the customer).

f. FSPs should have an agreement with their customers as to how clotted samples are reported as being unsuitable for analysis.

g. Training should be provided to laboratory staff in ensuring blood samples are free-flowing and to aid the identification clots in blood samples.

h. Training should be provided to reporting scientists to provide awareness of the implications of clots in s5A blood samples.

2.2.2. Where automated liquid handling instruments are using for the dispensing of whole blood samples, considerations should be made for the ability of the instrument to detect the presence of a clot in the sample.

2.3. Blank (analyte-free) matrices

2.3.1. Human blood should be used as the blank matrix for negative controls and in the preparation of calibrators and quality controls (QCs).

2.3.2. It is acknowledged that interferences can arise from the use of transfusion blood as the blank matrix, resulting in matrix effects. Matrix effects are defined as the combined effect of all components of the sample other than the analyte on the measurement of the quantity ^{[footnote 4]}. Matrix effects can result in the suppression or enhancement of the signal of the target analytes and the internal standard (ISTD) ^{[footnote 5]}.

2.3.3. Where non-matrix matched blood (e.g., transfusion blood) is used as the blank matrix, this should be validated to demonstrate there is no impact on the calculated concentration of case samples. This can be demonstrated by:

a. At validation, FSPs should aim to analyse a minimum of six different sources/lots of blank matrix (from multiple suppliers, where possible) to demonstrate the absence of common interferences ^{[footnote 6]} ^{[footnote 7]}.

b. Calibrators and QCs (at multiple concentrations in the calibration range) should be spiked into a minimum of six sources/lots of blank matrix and extracted alongside matrix-matched calibrators and QCs. Results should be scrutinized to show that use of the selected matrix does not impact the accuracy and precision of the QCs.

c. Prior to each new lot of matrix coming into use, FSPs should extract and analyse using full-scan mass spectrometry over a time period that would cover at least three injections (e.g., for a 5-minute method run time, the matrix extract should be analysed for a period of 15 minutes to allow identification of potential late-eluting interferences). The results should be reviewed to allow the identification of regions with interference that have the potential to enhance or suppress analytes of interest or ISTD signal and where present, actions should be taken to minimise the impact of the interference or the matrix lot should not be utilised. An approach to this is set out in ANSI/ASB 036 8.6.2 Post-column Infusion to Assess Ionization Suppression/Enhancement ^{[footnote 8]}.

2.3.4. Regardless of the source of the blank matrix, FSPs should ensure the preservative is matched to case samples (~2% weighed-in sodium fluoride). Calculations and weighing undertaken to achieve this should be recorded.

2.4. Maximum sample analyses

2.4.1. Case samples should be analysed a maximum of three times as a result of analytical failures for a single reason (batch- or sample- specific).

2.4.2. Case samples should be analysed a maximum of four times as a result of analytical failures for multiple reasons (batch- or sample- specific).

2.4.3. Where a result cannot be obtained by the maximum number of analyses, the sample should be reported as unsuitable for analysis, with an explanation as to the failures. This is to promote the investigation and resolution of analytical issues above persistent reanalysis of case samples.

2.5. Replicate consistency

2.5.1. The Code (94.4.3.k.) stipulates that for an arithmetic mean of a number of analytical results to be accepted, the replicates shall be in the range of ±20% of the mean. This guidance recommends that for an arithmetic mean of a number of analytical results to be accepted, the replicates should ideally be in the range of ±15% of the mean.

2.6. Reporting thresholds

2.6.1. To be reported as ‘not detected’, the sample should contain no drug(s) above the limit of detection (LOD) satisfying analytical parameters for confirmation.

2.6.2. Where a drug is detected in a sample between the LOD and the lower limit of quantification (LLOQ), where all other sample-specific analytical criteria are satisfied (including internal standard response), this should be reported as ‘detected below the LLOQ’ with the LLOQ concentration declared.

2.6.3. Samples with no drug(s) detected, or detected below the LLOQ can be reported in the event of a positive quality control failure for the relevant analyte(s), as per 2.6.1 and 2.6.2. Results between the LLOQ and the common reporting threshold (CRT) may be reported qualitatively as ‘detected below the specified limit’ in the event of a positive quality control failure for the relevant analyte(s).

2.6.4. Results between the LLOQ and the CRT should not be reported qualitatively as per 2.6.3 in the event of an analyte failure due to contamination, see 4.5.7.

Question 3

Environmental requirements

Accepted Answer

3.1. Environmental monitoring

3.1.1. Environmental monitoring should be conducted at least monthly for all s5A drugs. More frequent environmental monitoring should be completed where there is unusual activity, such as building work, being conducted within the proximity of the laboratory.

3.1.2. The laboratory should define areas where environmental monitoring is to be completed, this should include defining “critical” and “non-critical” areas. FSPs should map the end-to-end process of s5A samples to understand potential entry points for environmental contamination. Risks should be identified and assessed for each step of the process.

a. When defining “critical” areas for testing, FSPs should consider the areas;

i. S5A sample receipt

ii. S5A sample booking in

iii. S5A sample extraction

iv. S5A reagent preparation

v. S5A instrumentation

vi. Staff Personal Protective Equipment areas (i.e., where staff put on their lab coats).

b. Critical areas should be tested in every round of environmental monitoring.

c. The size of the critical area should be defined such that a sufficient proportion is swabbed to maximise detection of any contaminants.

d. When defining “non-critical” areas, the laboratory should consider;

i. Offices.

ii. Staff communal areas.

3.1.3. The laboratory should take measures to identify root cause where critical areas show evidence of contamination of s5A drugs. Consideration should be made for halting s5A analysis until the laboratory’s assessment confirms the contamination event is not adversely impacting case results and has been eliminated (i.e., follow-up environmental swabs are free from contamination).

3.1.4. The laboratory should define an acceptance threshold for detecting any s5A drug in an environmental monitoring swab of a “non-critical” area such that it minimises the risk of transfer into the critical area. Where a non-critical swab returns positive for a s5A drug, an impact assessment should take place to identify any potential risks to case results.

3.2. Anti-contamination measures

3.2.1. FSPs should continually seek ways to prevent and minimise contamination.

3.2.2. The approach to contamination in s5A analysis should consider:

a. Preventing

i. Risk assessment of each stage of the sample process.

ii. Physical separation of submission (goods and exhibits) areas and sample extraction areas.

iii. Regular washing or changing of PPE.

iv. Cleaning of work surfaces before and after s5A extraction.

v. Daily and weekly cleaning regimes.

vi. Screening of blank blood matrices.

vii. Staff training to encourage awareness and personal responsibility for minimising contamination events and escalating risks.

b. Detecting

i. Environmental monitoring (3.1).

ii. Analytical monitoring (4.5).

iii. A blank solvent injection should be run on instrumentation prior to loading analytical batches. Should the injection contain any s5A drug, actions should be taken to resolve this and the batch should not be run until a solvent blank injection is shown to be free of s5A drugs.

c. Resolving

i. Determining whether the incident is isolated or persistent.

ii. Determining source and root cause of the incident.

iii. Taking action to eliminate the source.

iv. Additional reactive cleaning measures.

d. Recording

i. The source(s) of the contamination (e.g., place in the analytical batch, sample type) should be specified in any quality investigation to assist efficient root cause analysis.

ii. Prompt and detailed documentation of steps taken to resolve the incident should be documented within the laboratory’s Quality Management System (QMS).

iii. Procedures should be updated to reflect any lessons learned.

e. Reporting

i. Considerations should be made for the potential impact of any recent contamination event on case results.

ii. Where a reliable result cannot be obtained for a s5A drug after 3 analyses due to contamination a statement to this effect will be provided on the report.

3.3. Cocaine contamination

3.3.1. Cocaine can be a persistent contaminant in toxicology FSPs and increasing sensitivity of instrumentation means that it can be challenging to eliminate cocaine contamination completely. It is essential that cocaine contamination is managed and that measures are taken to detect, investigate and monitor cocaine contamination events so that FSPs can be confident there is no impact on the outcome of a case.

3.3.2. FSPs should have specific measures in place to prevent, reduce and monitor occurrences of cocaine contamination, this should include:

a. Separation of exhibit types during transportation.

b. Evidence of cleaning regimes for courier vehicles transporting exhibits.

c. Wiping down of outer packaging of goods received (outer exhibit transport bags, consumables packaging).

d. Submission areas for drug and toxicology exhibits should be kept separate.

e. Staff movements between critical and non-critical areas should be mapped to identify potential mechanisms of transfer and hot spots.

f. Staff should wash hands thoroughly upon each entry to the laboratory.

g. Air vents should be swabbed in environmental monitoring to identify spikes in airborne cocaine levels.

h. Cocaine contamination events in analytical batches should be recorded on a contamination log spreadsheet, this spreadsheet should be reviewed monthly to enable escalation of any increase in cocaine contamination incidences. Where this occurs multiple times in an analytical batch (e.g., in several case samples) the incidences should be recorded individually.

3.3.3. It is imperative that incidences of cocaine contamination are recorded and reported appropriately. FSPs should open an ongoing annual quality investigation for cocaine contamination in relation to s5A analysis. Any incidences of cocaine contamination within the year should be individually and appropriately investigated as they occur, but all incidences (environmental or analytical) should be recorded promptly and chronologically under the same quality investigation record to allow for annual trend analysis.

3.3.4. For any incidence of cocaine contamination that persists and cannot be resolved within two weeks by the laboratory- reporting of s5A cocaine results should stop and this should be referred to the FSR. The FSR will request annual trending data in assessing the referral.

Question 4

Analytical requirements

Accepted Answer

4.1. Calibration

4.1.1. R2 may be used to assess the fit of the calibration curve. Other goodness-of-fit models may be used where the laboratory can evidence that the approach is robust and is as good as or superior to that of R2.

4.1.2. R2 is vulnerable to manipulation by removal of calibration points. Calibration points should not be excluded from the calibration curve solely to increase R2.

4.1.3. Regardless of the goodness-of-fit model utilised, calibration points should only be excluded as a result of an identified catastrophic failure as stipulated in the Code (94.4.3.e.iv), or if the calibrator’s ion ratios fail.

4.1.4. Calibration points should not be excluded solely as a result of an outlier test or due to failing an accuracy requirement, as this cannot be identified in a case sample.

4.1.5. Where a calibration point is excluded from the calibration curve, an impact assessment should be conducted on results around the CRT. Any cases where the exclusion has an impact on the outcome of the case (i.e., whether the result is reported as above or below a specified limit) should be logged for repeat analysis.

4.1.6. Calibration point exclusions should be recorded and monitored to allow for trend analysis in monthly reviews on an instrument-by-instrument basis.

4.2. Signal-to-noise ratio

4.2.1. Where a signal-to-noise ratio is used to identify a chromatographic peak, the minimum accepted ratio should be 3:1.

4.2.2. Where a signal-to-noise ratio is used in accepting a peak for quantitation, the minimum accepted ratio should be 10:1.

4.3. Internal standard

4.3.1. Internal standard (ISTD) recovery should be monitored using two mechanisms;

a. Relative ISTD response of each injection compared to the ISTD response of the batch.

i. The laboratory should calculate the mean ISTD response of the calibrators, QCs, case samples, and negative controls that contain ISTD.

ii. Relative ISTD acceptance criteria should be analyte-specific and set at validation. The criteria should then be reviewed after 30 casework batches have been analysed, whereby updated criteria can then be applied.

iii. Relative ISTD acceptance criteria should be set no worse than - 50% to +200% ISTD response from the mean batch ISTD response to allow for identification of half addition or double addition of ISTD during the extraction process.

iv. It is accepted that the laboratory may alternatively wish to assign relative ISTD acceptance criteria against the Reflow and Refhigh determined from the ISTD response of accepted calibrators and QCs, as set out in European Bioanalysis Forum: recommendation for dealing with internal standard variability ^{[footnote 9]}.

b. Absolute minimum response recovery for each ISTD (as per the Code 94.4.3.l.iv).

i. This should be calculated at validation.

ii. Where the ISTD response in any sample type falls below the assigned absolute minimum, the result should be rejected and should be not included in any calculation of the relative ISTD response acceptance criteria for the batch.

4.3.2. Where a single replicate fails to meet the relative ISTD response acceptance criteria, the result should only be accepted where:

i. The calculated concentrations of the replicates are consistent (within 15% of the mean of the replicates as per 2.5.1.).

ii. The other replicate has an acceptable relative ISTD response.

iii. Both replicates have an ISTD response above the absolute minimum.

iv. Both replicates satisfy all other analytical criteria.

4.3.3. The laboratory should determine a suitable threshold for the coefficient of variation (%CV) per ISTD, to be applied to each analytical batch. This should be initially calculated at validation then reassessed after 30 case batches.

4.3.4. The %CV for each ISTD should be calculated per analytical batch, and where this is greater than the threshold, the results for the corresponding analyte should be rejected.

4.3.5. Individual samples should not be excluded from the ISTD %CV calculation solely to bring the %CV within the assigned threshold. Case samples may be excluded from the %CV calculation should they fail the relative ISTD response criteria or minimum ISTD response requirement and the result is being rejected.

4.3.6. Matrix effects have the potential to significantly impact ISTD response. The method should demonstrate at validation that any variation in ISTD response due to matrix effects does not impact the calculated concentration of case samples and QCs.

4.3.7. FSPs should plot the ISTD responses for each analytical batch in a manner that allows trends or irregularities to be identified.

4.3.8. Where a trend or irregularity in ISTD is identified within an analytical batch, the laboratory should investigate to assess any potential impact on the calculated concentration of the case samples before the results on the batch can be accepted.

4.4. Positive quality control

4.4.1. Statistical method monitoring

a. Shewhart charts and Westgard rules should be used to assess positive QC performance.

b. Westgard rules should be used on Shewhart charts to identify when a method is out of control.

c. The mean concentration of the individual QC replicates should be plotted on the Shewhart chart as a single datapoint to reflect reporting of case results.

d. All datapoints, regardless of the standard deviation (s.d.) from the mean, are valid datapoints and should be plotted on Shewhart charts unless the cause of the failure is identified as per 4.4.1.e.i-v.

e. Datapoints should only be excluded from Shewhart charts due to an identified, catastrophic failure, or a failure that could also be clearly identified in a case sample. Examples include:

i. Incorrect spiking of working solution

ii. Incorrect or no addition of ISTD

iii. Disparate replicates

iv. Ion ratio failure

v. Contamination event identified (in a QC sample)

f. Exclusions of datapoints from Shewhart charts should be documented and reviewed to allow trend analysis.

4.4.2. Setting Shewhart chart limits

a. The intermediate precision should be used to calculate Shewhart chart limits. As datapoints within a single analytical batch are repeatability data and not reproducibility data, ANOVA should be used to calculate the intermediate precision, as the square root of the sum of squares of the within batch and between batch precision (see Eurachem Appendix C ^{[footnote 10]}).

b. As per 94.4.21 of the FSR’s Code of Practice, QC chart data and Shewhart Chart limits are to be reviewed at least every three months using t- and F- tests (a confidence level of k=2 or 95% should be used). Where this section says “with the values used to set the chart limits”, this describes the set of data most recently used to assign Shewhart Chart limits. It does not mean the new dataset should always be compared against the validation data or data used to set the initial limits (see 94.4.14 of the Code for definition of initial limits).

c. Differences in laboratory case volume and analytical batch frequency (and therefore the resulting number of datapoints) can cause significant implications for assigning a standard dataset size to be used when reviewing Shewhart chart limits. Further work is being conducted in this area to develop a statistical approach to determining dataset size for Shewhart chart reviews.

d. FSPs should specify the frequency at which Shewhart Chart limits are reviewed in their Standard Operating Procedures (SOPs), so the approach cannot be amended upon the resulting data.

e. Westgard rules may also indicate when it may be appropriate to review Shewhart Chart limits.

4.4.3. Uncertainty of measurement (UoM) calculations

a. Calculating initial UoM at validation

i. Both bottom-up and top-down approaches are suitable for calculating UoM at validation.

ii. Where using a top-down approach, the laboratory should calculate the intermediate precision as per 4.4.2.a.

iii. Where using a bottom-up approach, the laboratory should as a minimum consider uncertainty associated with certified reference materials, pipetting (of working solutions and analytical batches), volumetric flasks and the analytical measurement variability under repeatability (within batch) conditions (with considerations for avoiding double counting). An example of the bottom-up approach is set out in European Network of Forensic Science Institutes (ENFSI) Guidelines ^{[footnote 11]}.

b. Calculating ongoing UoM

i. FSPs should use a top-down approach to calculating ongoing UoM.

ii. UoM should be calculated using data combined from all instruments. Where a laboratory chooses to initially calculate UoM per instrument, the uncertainties should then be combined to assess the UoM of the whole method, as the UoM of the whole method is required to be compared to the Forensic Science Regulator’s Expanded Uncertainty (FSREU).

iii. The precise best practice methodology for calculating UoM for s5A measurements is still to be determined, it is widely accepted that FSPs should use a harmonised approach but this is a complex statistical area that is under development. General guidelines recommend inclusion of estimates of the bias, uncertainty of the bias, uncertainty of the CRM value and method uncertainty (via the intermediate precision) in UoM calculations ^{[footnote 10]} ^{[footnote 12]}.

iv. Significance tests should only be used to detect possible changes in Shewhart chart limits and should not be used to determine which information should be included in UoM calculations (e.g., bias). This mitigates the risk of a meaningful contribution being excluded.

v. UoM should be reviewed alongside Shewhart Chart limits, at least every three months.

vi. Where a new dataset is used to reassign Shewhart Chart limits, the data used to next calculate the UoM should begin from that point.

vii. Datapoints should only be excluded from UoM calculations in the event of an identified catastrophic failure.

viii. All data points, regardless of s.d. from the mean, are considered valid and should be included in the UoM calculations unless the cause for the failure has been identified, as set out in 4.4.1.e.i-v.

ix. Exclusions of datapoints from UoM calculations should be documented and reviewed to allow for trend analysis.

x. FSPs should be aware that a method with a high UoM over a short time period might be masked where there is a high volume of datapoints. A high UoM may be picked up more promptly at a laboratory with fewer datapoints available to use in UoM calculations.

4.4.4. Analytical batch failures

a. Failure of any QC within a batch should result in an investigation of the failure for the relevant analyte(s).

b. Where no cause can be identified, this should result in the failure of the analytical batch and repeat of all positive case samples.

c. Failure of a QC (excluding the limit concentration QC) can be accepted if the cause of the failure is identified and at least 10% of the samples in the batch remain as passing QCs (as per 94.4.8 of the FSR Code Version 2), i.e., in a batch of 30 samples, at least 3 passing QCs remain, including the limit QCs. Reasons may include:

i. Vial breakage.

ii. Disparate replicates.

iii. Incorrect or no addition of ISTD.

iv. Ion ratio failure.

4.5. Contamination

4.5.1. FSPs should actively monitor all samples (i.e., negative controls, positive controls, calibrants and case samples) in s5A analytical batches for contamination.

4.5.2. FSPs should define the analytical parameters that are used to identify a contamination peak in s5A analysis. However, any peak, regardless of peak area, occurring unexpectedly at the correct retention time for a s5A drug with passing qualifier ion ratios may indicate contamination and should be duly investigated.

4.5.3. FSPs should define a contamination threshold above which an analytical batch is rejected and repeated. FSPs may define their own thresholds, however, where contamination is confirmed below the threshold using the FSPs’ defined analytical parameters as per 4.5.2, the batch accepted and results utilised for the affected analyte, the contamination event should be declared on the affected reports.

4.5.4. Where a potential contamination peak at the correct retention time with passing qualifier ion ratios has been investigated and contamination can be ruled out, for example it is determined to be integration of background noise in line with the laboratory’s criteria for defining this, no reference to contamination would need to be declared on the report. In such instances, the laboratory should record this investigation and the findings.

4.5.5. FSPs should assign their contamination thresholds in relation to peak response of the LLOQ to avoid complexities associated with calculating concentrations outside of the calibration range.

4.5.6. If FSPs assign their thresholds to permit a certain level of contamination, it is their responsibility to communicate the science as to how the allowed contamination does not impact the analytical result to the Criminal Justice System (CJS).

4.5.7. Any contamination event confirmed using the analytical parameters in 4.5.2 that breaches the FSPs contamination threshold, should result in repeat analysis of all case samples positive for the relevant drug on the analytical batch. Negative samples for the affected analyte(s) (as per 2.6.1) may be reported.

4.5.8. Where contamination events are recurring for an analyte, s5A analysis should stop. Analysis should only continue once the contamination has been resolved.

4.5.9. Adjustments to analytical results should not be made to account for contamination.

4.5.10. Cocaine contamination

a. It’s acknowledged that cocaine contamination presents a challenge for s5A analysis more than any other drug, therefore additional measures are required to monitor for cocaine contamination in analytical batches. As benzoylecgonine (BZE), the major metabolite of cocaine, is also on the s5A drug panel, cocaine:BZE ratios can be used to detect cocaine contamination.

b. The presence of cocaine in a case sample at or above the laboratory’s contamination threshold, in the absence of BZE, should result in the repeat of all samples positive for cocaine on the analytical batch.

c. Incidences of potential cocaine contamination, that should result in greater scrutiny of the analytical batch, with consideration for repeating all samples positive for cocaine include but are not limited to:

i. A case sample with a cocaine concentration greater than the BZE concentration.

ii. A case sample where the cocaine concentration is equal to the BZE concentration.

iii. A case sample where the cocaine concentration is above the common reporting threshold (CRT) and the BZE concentration is below the CRT.

iv. A positive control or calibrant where the cocaine concentration is greater than the expected variation, where this does not align with the performance of that point for other analytes on the same analytical batch.

v. Disparate case sample replicates results for cocaine and/or BZE.

d. Cocaine is known to impact analytical batches in two separate but potentially simultaneous mechanisms and actions to address either mechanism may differ:

i. Persistent levels of cocaine contamination across the analytical batch;

ii. Unpredictable, sudden spikes of cocaine contamination.

Question 5

Acknowledgements

Accepted Answer

5.1.1. This guidance was developed with advice from the FSR’s Section 5A Working Group, a sub-group of the FSR’s Drugs and Toxicology Specialist Group.

Question 6

Modification

Accepted Answer

6.1.1. This is the first issue of this document under section 9 of the Forensic Science Regulator Act 2021.

6.1.2. The PDF is the primary version of this document.

6.1.3. The Regulator uses an identification system for all documents. In the normal sequence of documents this identifier is of the form ‘FSR-###-####’ where (a) (the first three ‘#’) indicate letters to describe the type of document and (b) (the second four ‘#’) indicates a numerical code to identify the document. For example, this document is FSR-GUI-0029, and the ‘GUI’ indicates that it is a guidance document. Combined with the issue number this ensures that each document is uniquely identified.

6.1.4. If it is necessary to publish a modified version of a document (for example, a version in a different language), then the modified version will have an additional letter at the end of the unique identifier. The identifier thus becoming FSR-GUI-0029a.

6.1.5. In the event of any discrepancy between the primary version and a modified version then the text of the primary version shall prevail.

Question 7

Review

Accepted Answer

7.1.1. This document is subject to review by the Forensic Science Regulator at regular intervals.

7.1.2. The Forensic Science Regulator welcomes views on this guidance. Please send any comments to the address as set out at the following web page: www.gov.uk/government/organisations/forensic-science-regulator or send them to the following email address: FSREnquiries@forensicscienceregulator.gov.uk.

Question 8

Abbreviations and Acronyms

Accepted Answer

Abbreviation

CJS

Criminal justice system

CRT

Common reporting threshold

FSP

Forensic Service Provider

FSREU

Forensic Science Regulator’s Expanded Uncertainty

ISTD

Internal Standard

PPE

Personal protective equipment

QC

Quality control

QMS

Quality management system

RTA

Road Traffic Act 1988

S5A

Section 5A Road Traffic Act 1988 toxicology

UoM

Uncertainty of measurement

Published by:

The Forensic Science Regulator
23 Stephenson Street
Birmingham
B2 4BJ

www.gov.uk/government/organisations/forensic-science-regulator

Question 9

References

Accepted Answer

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Forensic Science Regulator, “Code of Practice (Version 1),” 2023. ↩
Forensic Science Regulator, “Code of Practice (Version 2),” 2025. ↩ ↩²
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