Freedom of Information Follow-Up — Cross-Reactivity and False Positive Safeguards in Drug Testing
Case reference FOI2026/00701
Received 7 July 2026
Published 4 August 2026
Request
Response
In accordance with section 1(1) of the Freedom of Information Act 2000 (FOIA), Oxford City Council (OCC) confirms that it holds some information falling within the scope of your request.
The answers below are based on OCC’s Alcohol and Drug Misuse Policy and Alcohol and Drug Testing Procedure. Those documents concern drug and alcohol testing involving OCC employees. They do not, by themselves, establish the testing procedures used by any separately commissioned substance misuse service provider.
The FOIA provides a right of access to recorded information held by FOIA. It does not require OCC to confirm or dispute the scientific propositions set out in a request where it does not hold a recorded assessment addressing those propositions.
1. Is your authority (and/or its commissioned substance misuse service
provider) aware of the cross-reactivity risks identified above? Has
any assessment been made of the likelihood of false positive results
from lawful sources when using immunoassay screening?
OCC’s Alcohol and Drug Misuse Policy and Alcohol and Drug Testing Procedure do not contain specific references to the cross-reactivity risks or individual substances listed in your request.
OCC has not identified a separate recorded assessment of the likelihood of false positive screening results arising from those lawful substances.
However, OCC’s testing procedure requires relevant information about prescribed and over-the-counter medication to be recorded. The procedure also provides for laboratory review and referral to an independent Medical Review Officer where prescribed medication may affect the interpretation of a test result.
2. Does the applicable drug and alcohol testing policy require that
all positive screening results are confirmed by a second, independent
analytical method — specifically GC-MS or LC-MS/MS — before any
disciplinary, safeguarding, or service-access decision is made?
OCC’s procedure requires a positive drug screening result to be confirmed through analysis of a further urine sample by an accredited laboratory before the result is finalised.
The procedure states that laboratory analysis is undertaken using two methods. However, the documents held by OCC do not specify whether those methods are gas chromatography–mass spectrometry or liquid chromatography–tandem mass spectrometry. OCC cannot therefore confirm from the recorded information held that either of those particular methods is used.
For alcohol testing, the procedure requires a second breath sample where an initial positive reading is obtained before action is taken.
OCC’s documents concern employment-related testing. They do not set out procedures for safeguarding or service-access decisions made by a commissioned substance misuse service provider.
3. If confirmatory testing is not routinely carried out, on what basis
are positive screening results treated as definitive?
This is not applicable to OCCs employee testing procedure because a positive drug screening result is not treated as final without confirmatory laboratory analysis.
4. Has your authority (and/or its provider) received any complaints,
grievances, or representations from individuals who attributed a
positive drug test result to any of the lawful sources listed above?
If so, how many in the last three years, and what was the outcome?
OCC has identified no complaints, grievances or representations of this description in OCC records searched for the three-year period preceding the date of your request.
There are therefore no recorded outcomes to provide.
5. What guidance, if any, has been issued to staff involved in drug
testing about the possibility of false positives from lawful
substances, and the appropriate steps to take before acting on a
screening result?
OCC’s policy and procedure require employees to declare prescribed and over-the-counter medication before testing.
Medication and other substance use during the preceding week must be recorded as part of the chain-of-custody process. A positive drug screening result requires confirmatory laboratory analysis before the result is finalised. The procedure also provides for referral to an independent Medical Review Officer where prescribed medication may be relevant to the interpretation of the result.
The policy and procedure do not contain separate guidance specifically addressing each of the substances listed in your request.
In accordance with section 16 of the FOIA, which relates to the duty to provide reasonable advice and assistance, OCC has clarified that the answers above concern its internal employment-related policy and procedure.
If your request is intended to cover the separate clinical or operational testing arrangements used by a particular commissioned substance misuse service provider, it would assist OCC if you identified the relevant service or provider. A more targeted request could ask for the provider’s current drug-testing policy, the types of screening and confirmatory tests used, the circumstances in which confirmatory testing is required, guidance concerning cross-reactivity and false positive results, and the number of relevant complaints received during a specified period.
Should a contractor hold information on OCC’s behalf, that information may be treated as held by OCC for the purposes of section 3(2)(b) of the Freedom of Information Act 2000.
If you disagree with any part of the response to your request, you are entitled to ask the Council for an internal review of the decision(s) made. You may do this by writing to the Monitoring Officer, by either email monitoringofficer@oxford.gov.uk – or by post to Monitoring Officer, Oxford City Council, Town Hall, St Aldate’s, Oxford, OX1 1BX. After the result of the internal review, if you remain dissatisfied, you may ask the Information Commissioner to intervene on your behalf. You may do this by writing to the Information Commissioner's Office, Wycliffe Lane, Wilmslow, Cheshire, SK9 5AF.
Yours sincerely,
Freedom of Information Officer
| Freedom of Information Team | Law & Governance | Oxford City Council | Town Hall | St Aldate’s | Oxford | OX1 1BX |
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