Laboratory analysis is the stage at which a collected sample becomes a number. It is also the stage most often misread, because an accreditation logo, a detection limit and a reported unit each mean something narrower than they appear to. This page describes what happens after a sample reaches the laboratory, what accreditation does and does not cover, and how a certificate of analysis should be read.
Laboratory analysis begins when a sample is received and registered. Its purpose is to determine whether the target agent is present and, where the method permits, the mass, concentration, count or other quantity found in the submitted sample.
The laboratory normally checks the sample identifier, analytical request, medium, condition on arrival, preservation requirements and reported collection volume or time. Any inconsistency may need to be resolved before analysis begins. Examples include an identifier that does not match the submission record, a damaged container, an expired medium or an insufficiently documented sample.
These checks do not establish whether the sample was representative of workplace exposure. That question belongs to workplace exposure monitoring and exposure assessment strategy. The laboratory can analyse only the material received and the information supplied with it.
Chain-of-custody records provide continuity between receipt, storage, preparation, analysis and disposal or return. Laboratories may also retain an audit trail showing who handled the sample, which instrument and method were used, when quality-control checks were completed and whether any result was amended.
ISO/IEC 17025 is the international standard for the competence, impartiality and consistent operation of testing and calibration laboratories. Accreditation bodies use it when assessing whether a laboratory is technically competent to perform specified activities. The current ISO/IEC 17025:2017 edition remained current following its confirmation in 2023. ISO describes the standard as a framework for producing valid and reliable results.
Accreditation is granted for a defined scope rather than for every activity undertaken by a laboratory. A laboratory may be accredited for one method, analyte, matrix or measurement technique but not another. The accreditation certificate and schedule should therefore be checked for the laboratory's legal identity and location; the accreditation body and certificate number; the analytical method; the target analyte or group of analytes; the sample matrix or medium; the measurement technique; and any qualification, exclusion or modified method.
A general statement that a laboratory is "ISO 17025 accredited" is incomplete unless the requested analysis falls within its published scope. An unaccredited result produced by an otherwise accredited laboratory should be identified as outside scope and should not display an accreditation symbol in a misleading way.
AIHA Laboratory Accreditation Programs, LLC operates several ISO/IEC 17025-based programmes. The programme most directly associated with workplace exposure analysis is the Industrial Hygiene Laboratory Accreditation Program, or IHLAP. It is intended for laboratories analysing samples used to evaluate occupational exposure or contamination arising from occupational activities. AIHA-LAP describes IHLAP as an accreditation programme specifically for workplace-exposure analysis.
Other AIHA-LAP programmes have different purposes: the Environmental Lead Laboratory Accreditation Program covers specified environmental lead matrices, including air, paint, soil and settled dust; the Environmental Microbiology Laboratory Accreditation Program covers defined microbiological examinations of air, surface, liquid and bulk samples; the Unique Scopes Laboratory Accreditation Program accommodates testing outside the established programme categories; and separate programmes cover food testing and certain field or mobile beryllium analyses.
Programme membership alone does not show that every method is accredited. The laboratory's current scope remains the controlling document. AIHA-LAP also requires relevant proficiency-testing participation for IHLAP categories. Proficiency testing provides an external comparison by asking laboratories to analyse samples containing values unknown to them and comparing their performance with assigned values or peer results.
AIHA-LAP accreditation is a recognised means of demonstrating competence. It does not create a UAE legal requirement to use a particular laboratory or accreditation programme.
Industrial hygiene laboratories receive several forms of sample medium. The medium reflects the agent class and validated analytical method, although the selection of chemical monitoring media belongs to a separate subject.
Particulate samples commonly arrive on filters or within filter-containing cassettes. Depending on the requested analysis, the laboratory may determine total collected mass, digest the deposit for elemental analysis, extract a soluble component or examine fibres or particles microscopically.
Vapour samples may arrive on solid sorbent tubes, treated filters, passive badges or containers holding a whole-air sample. Analysis may involve gas chromatography, liquid chromatography, mass spectrometry, infrared techniques or another validated detector system.
Gas samples may be submitted in bags, canisters, evacuated vessels or chemically treated collection media. Some methods determine a specific gas, while others screen for a broader group of compounds. The certificate should distinguish a targeted analysis from a non-targeted screen.
Surface samples may include wipes, swabs, adhesive lifts or bulk fragments. These matrices do not directly represent airborne inhalation exposure. Results may instead describe surface loading, presence, composition or material content.
Biological specimens used for biological monitoring may include urine, blood or exhaled breath, but their handling, confidentiality and interpretation require an appropriate clinical and occupational-health framework. Such analysis is distinct from health surveillance and should not be treated as an automatic indication of disease.
The limit of detection, or LOD, is the lowest amount that can be distinguished from analytical background with a stated level of confidence. It indicates detectable presence, not necessarily a quantity that can be reported with acceptable precision.
The limit of quantification, or LOQ, is generally higher. It represents the lower level at which the method can provide a numerical result meeting specified performance criteria. Laboratories may use related terms such as reporting limit, method detection limit or practical quantification limit. Definitions should be checked rather than assumed to be interchangeable.
A result reported as "less than the LOQ" does not mean that the analyte is absent. It means that any amount present could not be quantified reliably below that threshold. Similarly, "not detected" means that the analytical response did not exceed the method's detection criterion under the conditions of analysis.
Detection capability may depend on the blank response, preparation volume, instrument sensitivity, dilution, sample loading and the volume of air associated with the submitted sample. A result can therefore be analytically valid yet insufficiently sensitive for the assessment question.
Measurement uncertainty describes the range within which the value attributable to the measured quantity is reasonably believed to lie. It reflects recognised contributors such as calibration standards, repeatability, instrument response, sample preparation, recovery and blank variability.
Uncertainty is not evidence that the result is unreliable. Every measured value has uncertainty. The important questions are whether it has been evaluated appropriately and whether it is small enough for the intended decision.
Laboratory quality control may include reagent blanks, media blanks, duplicate analyses, matrix spikes, certified reference materials, calibration checks, recovery studies and continuing instrument-performance checks. Results outside acceptance criteria may lead to reanalysis, investigation, qualification or rejection.
The laboratory's uncertainty estimate normally covers the analytical stage. It may not include variability from workplace conditions, worker behaviour, sample positioning or collection volume. Those wider sources of uncertainty belong to the exposure assessment.
A certificate of analysis should be read from the identification details through to the qualifications and notes. The following items are particularly important: laboratory name, address and accreditation details; report number, issue date and page numbering; sample identifiers matching the submission record; dates of receipt, analysis and, where relevant, preparation; analyte, method, matrix and analytical technique; reported result and unit; LOD, LOQ or reporting limit; blank correction or recovery information where applicable; uncertainty statement where relevant; accreditation status of each test; authorised signatory; and deviations, qualifications or amended-result history.
The reported units require close attention. A laboratory may report mass per sample, mass per filter, number per field or concentration in an extract. Conversion to an airborne concentration may occur elsewhere and depends on valid collection information. A laboratory result should not be compared directly with an airborne exposure benchmark unless the units, averaging period and measured quantity are compatible.
A laboratory may be accredited for one method, analyte, matrix or measurement technique but not another. A general claim of ISO 17025 accreditation is incomplete unless the requested analysis falls within the published scope.
A result reported as less than the limit of quantification does not mean the analyte is absent. It means any amount present could not be quantified reliably below that threshold.
Measurement uncertainty is not evidence that a result is unreliable. The questions are whether it has been evaluated appropriately and whether it is small enough for the decision being made.
A laboratory may report mass per sample, mass per filter, number per field or concentration in an extract. A laboratory result should not be compared with an airborne exposure benchmark unless units, averaging period and measured quantity are compatible.
ISO/IEC 17025 accreditation and AIHA-LAP programme membership are recognised means of demonstrating laboratory competence. Neither creates a UAE legal requirement to use a particular laboratory or accreditation programme, and neither substitutes for competent fieldwork or professional interpretation. Accreditation is granted for a defined scope, so the controlling document is always the laboratory's current schedule rather than a general statement on a report cover.
Foreign standards and accreditation programmes are evidence of recognised practice. They do not become binding in the UAE merely because they are technically established elsewhere.
No. Accreditation applies to the activities listed on the laboratory's current scope. A result may be outside scope even when issued by an accredited laboratory.
The LOD concerns reliable detection, while the LOQ concerns reliable numerical measurement. A substance may be detected at a level too low to quantify accurately.
No. It means that the analytical response did not exceed the method's detection threshold. A smaller amount may still have been present.
Qualification may be necessary because of damage, contamination, excessive loading, poor recovery, dilution, holding-time exceedance, interference or another departure from the method.
Not by itself. It reports analytical findings. Exposure interpretation also requires collection information, representativeness, averaging time, uncertainty and the applicable assessment framework.