DYK #2 -Behind the Results: What Supports a Reported Laboratory Result?

A reported laboratory result may be supported by dozens of quality-control activities.

A laboratory result is more than a number generated by an instrument. Depending on the method, matrix and regulatory program, it is supported by calibration, contamination checks, recovery and precision data, sample-specific evaluations and documented review.

For consultants, understanding the evidence behind a result can make report review more efficient. It helps clarify what to look for when a result is qualified, when an exception is noted, or when project requirements call for a closer look at data usability.

 

The evidence behind a reported result

Alongside client samples, a laboratory may analyze standards, blanks, spikes, duplicates, surrogates and other performance checks. These controls help demonstrate whether the method was operating as expected and whether sample-specific conditions may affect the result.

The exact controls vary, but most address one of six questions:

Quality-control category	What it helps demonstrate	Examples
Instrument performance	The instrument was calibrated, stable and capable of identifying the target analytes at the required sensitivity.	Initial calibration, second-source and continuing calibration verification, retention-time or identification criteria, tune or performance checks
Cleanliness	The reported result was not caused by laboratory contamination or carryover.	Instrument, method, preparation and reagent blanks; carryover checks
Accuracy	The method can recover known amounts of the target analytes.	Laboratory control samples, reference materials, calibration-verification standards and surrogate recoveries
Precision	Repeated measurements are acceptably consistent.	Laboratory duplicates, matrix spike duplicates, duplicate preparations and replicate analyses
Matrix impact	The sample itself has not introduced an unrecognized bias or interference.	Matrix spikes, surrogate recoveries, dilution checks and interference evaluations
Traceability and review	The work can be reconstructed, evaluated and technically reviewed.	Chain of custody, sample-handling records, preparation logs, standards and equipment records, instrument run logs and technical review

No individual control tells the whole story. A clean blank does not, by itself, demonstrate accuracy. An acceptable spike recovery does not replace instrument-performance checks. Together, the controls create the evidence used to evaluate whether results are technically supportable and to communicate any relevant limitations.

 

Quality control helps identify exceptions

Quality control does not mean exceptions never occur. Environmental matrices can be complex, instruments can drift, and contamination, interferences or recovery issues can arise.

The value of the QC system is that it identifies these conditions so they can be evaluated.

Depending on the situation, the laboratory response may include reanalysis, recalibration, additional review, a corrective action, qualification of affected data, or an explanation in the final report. The appropriate response depends on the method requirements, the nature of the exception and its potential impact on associated results.

For a consultant, that means an exception is not automatically an unusable result. It is an indicator to review the supporting information: what occurred, which samples may be affected, how the laboratory assessed the impact and how that assessment is documented.

Quality assurance makes the work traceable

Quality control evaluates how the analytical process performed. Quality assurance provides the broader system that makes the work traceable after the fact.

That documentation may include:

• Sample receipt, handling, preservation and holding-time records
• Standards, reagents, consumables and support-equipment records
• Instrument calibration and maintenance information
• Preparation and analytical procedures
• Analyst activities, technical review and reporting decisions

This traceability matters because environmental data may need to support project decisions long after analysis is complete. The relevant question is not only, “What was the result?” but also, “What evidence supports it, and are any limitations clearly documented?”

 

A practical report-review check

When reviewing a laboratory report or data package, consider:

 

• What QC evidence supports the reported results?
• Are any blanks, recoveries, duplicates or matrix checks outside acceptance criteria?
• Which samples, analytes or results are associated with the exception?
• How has the laboratory evaluated and explained the potential impact?
• Do the report, qualifiers and supporting records provide the information needed for the project’s review?

ALS applies method-specific quality-control and quality-assurance processes designed to substantiate and reconstruct reported results. These processes help demonstrate method performance, identify exceptions and provide the supporting evidence behind environmental data.

 

The result is only as reliable as the evidence supporting it.

Have questions about laboratory quality control, quality assurance or the supporting evidence behind your environmental testing results? Contact ALS to learn how our team can support your testing needs.