What an accredited lab actually does

Accreditation is a narrower claim than it sounds. It is a formal finding, made by an accreditation body after an on-site assessment, that a laboratory is competent to carry out a specific list of tests or calibrations and to report the results reliably. The international standard behind that finding is ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories. A lab that holds accreditation has been examined against that document and is examined again on a cycle.

The word that carries the weight is “specific.” Accreditation is granted for a scope: a published list of the tests, the materials or matrices they apply to, the methods used and, often, the measurement ranges. A laboratory accredited to measure water content in solids by one method is not accredited for anything else on the strength of it. When a report says a result came from an accredited lab, the useful question is whether that particular test sits inside the lab’s scope.

What the assessors look at

ISO/IEC 17025 asks two kinds of things of a lab. The first are structural: the lab must be impartial, must protect clients’ confidential information, and must run a management system with document control, internal audits, corrective action and periodic review by management. The second are technical, and they are where most of an assessment’s time goes.

• Personnel are trained, and their competence for each task is assessed and recorded, not assumed.
• Equipment is calibrated, and the calibrations trace back through an unbroken chain to national or international measurement standards.
• Methods are validated, or, for standard methods, verified to work in this lab’s hands.
• Measurement uncertainty is evaluated, so a result can be stated with an honest margin.
• Results are monitored over time, through control samples and through comparison with other labs.
• Samples are handled, identified and stored so that what is tested is what was received.

Assessors do not only read procedures. They watch analysts work, pull records at random and follow a result backward: from the report to the raw data, to the instrument log, to the calibration certificate, to the training record of the person who ran the test. A lab that writes good procedures and does not follow them tends to be found out at this step.

Proficiency testing

One of the more revealing requirements is participation in proficiency testing. A scheme provider sends portions of the same material to many laboratories, each lab analyzes it without knowing the expected value, and the provider compares every result with an assigned value. A lab whose result falls outside the acceptable range has to investigate why and record what it changed. Over several rounds this gives an outside, numerical check on whether the lab’s results agree with everyone else’s, which no internal audit can provide.

What ends up on the report

ISO/IEC 17025 also sets out what a test report must contain: a unique identification, the lab’s name and address, the client, the method used, a description and identification of the item tested, the date it was received and the dates of testing, the results with units, and the identification of the person authorizing the report. Where relevant, it also carries measurement uncertainty, and where a statement of conformity with a specification is made, the decision rule used to reach it. Reports are expected to state that the results relate only to the items tested.

Accredited labs may place the accreditation body’s mark on reports, under rules the body sets. Where a single report mixes accredited and non-accredited tests, the non-accredited ones are expected to be identified as such. That distinction is easy to miss and worth looking for.

What accreditation does not mean

Accreditation is a statement about a lab’s competence, not about any material it tests. A result from an accredited lab says what that lab measured on the item it received. It says nothing about whether the item was representative of a larger lot, whether it was handled properly before it arrived, or whether the lot it came from is still in the same condition months later. That is the meaning of the line stating that results relate only to the items tested.

Accreditation is also not permanent. Accreditation bodies carry out surveillance visits between full reassessments, and they can reduce a scope, suspend it or withdraw it. Most bodies publish a searchable directory of accredited labs with their current scopes, and that directory, rather than a mark on a document, is the authoritative place to check.

Accreditation bodies are themselves evaluated by their peers under the arrangements of the International Laboratory Accreditation Cooperation, ILAC. Bodies that sign the ILAC mutual recognition arrangement accept each other’s accreditations as equivalent, which is why a report from an accredited lab in one country can carry weight in another.

Checking it yourself

Three checks cover most of the ground. Find the lab in the accreditation body’s public directory and confirm the accreditation is current. Open the scope and confirm that the specific test, method and material type on the report are listed. Then read the report for the required fields: identification of the item, the method, the dates, units and an authorizing signature. A report that passes all three tells you a competent lab measured something. Whether that something represents what you hold is a separate question, answered by the sampling and handling record.