The Sample That Sat Too Long
A courier delivers a batch of 12 water samples to a laboratory at 4:10 pm on Friday. The samples were collected the previous morning and stored in an esky with ice, but the ice has largely melted by the time they arrive. The accompanying chain-of-custody form lists collection time as 9:00 am Thursday and specifies that samples should be refrigerated at 2–8 °C and analysed within 24 hours for the parameters requested. The laboratory closes at 5:00 pm and reopens Monday at 8:30 am. A technician, Aisha, is asked to sign for the samples and store them. She notices two sample bottles are unlabelled and one has a cracked lid.
1. Assess the condition of the samples against the acceptance criteria. Which samples should be accepted and which rejected, and why?
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Assessment against criteria:
- Holding time: Collected 9:00 am Thursday; arriving 4:10 pm Friday is about 31 hours - beyond the 24-hour analysis window for the requested parameters. Even if analysis began immediately, the holding time is exceeded.
- Temperature: The ice has melted, so the 2–8 °C requirement cannot be confirmed. Temperature excursion is likely.
- Labelling: Two bottles are unlabelled - they cannot be traced to a collection point and are unusable.
- Integrity: One cracked lid risks leakage and contamination.
Decision:
- The two unlabelled bottles must be rejected - no traceability.
- The cracked bottle must be rejected - compromised integrity.
- The remaining nine samples are outside holding time and have an unverified temperature history. They should be flagged as non-conforming. Whether they are analysed depends on the laboratory's policy and the intended use of results; if results must be defensible, they should be rejected or analysed only with a clear caveat recorded.
Aisha should not simply sign and store them as if compliant.
2. What should Aisha do procedurally, including documentation and communication?
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Procedural steps:
- Do not sign as compliant. Sign only to acknowledge receipt, noting the condition.
- Record a non-conformance - arrival time, collection time, temperature on arrival, holding time exceeded, labelling defects, cracked lid.
- Photograph the samples and the chain-of-custody form as evidence.
- Quarantine the non-conforming samples - store them separately (refrigerated if appropriate) so they are not mixed with compliant samples.
- Notify the laboratory supervisor and the client/courier as soon as practicable, before the 5:00 pm close if possible. The client needs to know results may be compromised and may need to reschedule sampling.
- Follow up on Monday - do not leave the issue unresolved over the weekend. If analysis is to proceed, record the caveat clearly.
- Review the courier/storage arrangements - melted ice and a 31-hour delay suggest a systemic problem worth addressing.
3. The client insists the samples be analysed anyway because resampling is expensive. How should the laboratory respond?
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The laboratory should not let commercial pressure override data integrity, but it can be pragmatic.
Response:
- Explain clearly, in writing, that holding time and temperature requirements were not met, and what that means for the reliability of results for the requested parameters.
- Offer options: (a) analyse with a formal caveat on the report stating the samples were received outside acceptance criteria; (b) analyse only parameters that are less time-sensitive, if any; (c) reject and resample.
- If the client chooses to proceed, record the client's instruction and the caveat in the file. The report must carry the limitation so no one later mistakes the results for fully valid data.
- The laboratory's quality system should define who can authorise analysis of non-conforming samples, and that authorisation should be documented.
Principle: The laboratory's obligation is to produce results that are honest about their limitations. Accepting the work is acceptable; presenting compromised results as compliant is not.