What to Look for in a Contract Testing Lab — A Manufacturer's Checklist

The Wrong Lab Can Cost You More Than the Right One Saves

Procurement teams often evaluate contract testing laboratories primarily on price and turnaround time. Both matter — but they are not the most important factors. A laboratory that delivers fast, inexpensive results that are not defensible, not reproducible, or not performed by a qualified analyst creates more problems than it solves.

We have seen manufacturers receive CoAs from contract labs that cited accreditation scopes that did not cover the tests performed, reported results without detection limits, used methods that had not been validated for the specific matrix, and could not produce raw data when requested. In each case, the manufacturer had to repeat the testing — at additional cost and delay — and in some cases had to investigate whether previously released lots were actually compliant.

Selecting a contract testing laboratory is a quality decision. This guide covers the criteria that matter most, the questions to ask before signing a testing agreement, and the ongoing performance indicators that tell you whether the relationship is working.

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Criterion 1: ISO 17025 Accreditation — Scope Matters

ISO/IEC 17025 accreditation is the international standard for testing and calibration laboratory competence. An accredited laboratory has demonstrated to an independent accreditation body that its management system, technical competence, and measurement traceability meet defined requirements.

Critical point: Accreditation is scope-specific. A laboratory may be ISO 17025 accredited for microbiology but not for pesticide residue analysis, or accredited for heavy metals by ICP-MS but not by AAS. When a laboratory tells you they are “ISO 17025 accredited,” ask for their scope of accreditation and verify that it covers the specific tests you need.

How to verify:

• Request the laboratory’s current accreditation certificate and scope document
• Cross-reference the scope against the accreditation body’s public registry (A2LA, NVLAP, PJLA, or the relevant national body)
• Confirm the accreditation is current (not expired) and covers the specific matrices you will be submitting

A laboratory performing tests outside their accreditation scope is not providing accredited results, regardless of what their CoA header says.

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Criterion 2: Method Validation for Your Matrix

A method that is validated for one matrix may not perform reliably in another. A heavy metal method validated for botanical extracts may have different performance characteristics when applied to a mineral supplement or a lipid-based ingredient. A microbial method validated for tablets may require modification for a probiotic product.

Questions to ask:

• Is the method validated for my specific matrix (not just the general category)?
• Can you provide method validation data, including accuracy, precision, linearity, and detection/reporting limits?
• If the method is a compendial method (USP, AOAC, ISO), have you performed method suitability testing for my specific product?
• If the method is in-house developed, what is the validation status and when was it last reviewed?

A laboratory that cannot answer these questions with specific data — not just general assurances — should be evaluated carefully before being added to your approved supplier list.

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Criterion 3: Turnaround Time and Communication

Turnaround time matters for production scheduling, but the more important question is reliability of turnaround time. A laboratory that promises 5-day turnaround but routinely delivers in 10 days creates more disruption than one that promises 8 days and consistently delivers in 7.

Questions to ask:

• What is your standard turnaround time for each test category?
• What is your on-time delivery rate for the past 12 months?
• Do you offer rush or expedited testing, and at what premium?
• How do you communicate delays — proactively, or only when asked?
• Who is my primary contact for questions about my samples and results?

For time-sensitive testing (e.g., microbial testing that gates production scheduling), ask specifically about the laboratory’s capacity during peak periods and their procedure for managing backlogs.

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Criterion 4: Raw Data Availability

A CoA is a summary document. The raw data — instrument output, calibration records, analyst worksheets, sample preparation records — is the underlying evidence that supports the CoA results. In the event of an out-of-specification result, a regulatory inquiry, or a customer dispute, you may need access to that raw data.

Questions to ask:

• Do you retain raw data for all tests, and for how long?
• Can I request raw data for any test result, and what is the process?
• Is raw data available in electronic format?
• Are instrument calibration and maintenance records available upon request?

A laboratory that cannot or will not provide raw data upon request is not a suitable partner for regulated testing. Under FDA’s data integrity expectations, raw data must be attributable, legible, contemporaneous, original, and accurate (ALCOA). If a laboratory cannot demonstrate these attributes, their results cannot be fully relied upon.

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Criterion 5: Reference Standards and Reagents

The quality of test results depends heavily on the quality of the reference standards and reagents used. For quantitative assays, the reference standard defines the calibration — a substandard reference standard produces inaccurate results.

Questions to ask:

• What reference standards do you use for [specific test]? Are they USP Reference Standards, certified reference materials (CRMs), or in-house prepared standards?
• How are reference standards stored, and how is their expiration tracked?
• For botanical identity testing, what authenticated reference materials do you use for HPTLC comparisons?
• For DNA barcoding, which reference database do you use, and how is it curated?

For high-value or high-stakes testing, consider providing your own authenticated reference standard to the laboratory. This eliminates one variable and gives you greater confidence in the calibration.

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Criterion 6: Regulatory Compliance Experience

Not all contract testing laboratories have experience supporting regulated supplement or cosmetic manufacturers. A laboratory that primarily serves the food industry may not be familiar with USP <61>/<62> microbial testing requirements, USP <232>/<233> elemental impurity limits, or the documentation requirements of 21 CFR Part 111.

Questions to ask:

• What percentage of your clients are dietary supplement or cosmetic manufacturers?
• Are you familiar with 21 CFR Part 111 documentation requirements for raw material testing?
• Have you supported clients through FDA inspections? What was the outcome?
• Can you provide references from supplement or cosmetic manufacturer clients?

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Criterion 7: Ongoing Performance Monitoring

Once you have selected a contract laboratory, ongoing performance monitoring is part of your supplier qualification program. Treat the laboratory as you would any critical raw material supplier.

Ongoing monitoring activities:

• Track turnaround time against agreed standards on every order
• Periodically submit blind samples (samples with known results) to verify accuracy
• Review CoA format and completeness on every report — method references, detection limits, analyst signatures
• Conduct periodic re-qualification reviews, including accreditation scope verification
• Establish escalation criteria: what triggers a formal performance review or change of laboratory?

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Practical Checklist: Contract Testing Lab Qualification

• ISO 17025 accreditation verified in accreditation body’s public registry
• Accreditation scope confirmed to cover all required tests and matrices
• Method validation data reviewed for key tests (accuracy, precision, detection limits)
• Method suitability testing confirmed for your specific product matrices
• Turnaround time commitments documented and on-time delivery rate verified
• Raw data retention policy confirmed and raw data access process documented
• Reference standard sourcing and management practices reviewed
• Regulatory compliance experience (21 CFR Part 111, USP methods) confirmed
• Laboratory added to Approved Supplier List with qualification date and scope
• Ongoing performance monitoring schedule established (blind samples, turnaround tracking, periodic re-qualification)
• Escalation criteria defined for performance failures