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A diagnostic laboratory is a facility that examines materials from the body, from humans or animals, to provide information about disease or health. In the United States, human-specimen labs are defined and regulated under the CLIA rules in 42 CFR Part 493, while animal-health labs are coordinated through networks such as USDA’s NAHLN. This page is general information for researchers, laboratory and clinic staff, not medical or veterinary advice.
Short answer
A diagnostic laboratory performs examinations on specimens to support diagnosis, prevention or treatment of disease. Under US federal rules for human testing, a site that only collects or prepares specimens, or only acts as a mailing service, is not a laboratory. What a lab is allowed to run depends on the complexity category of each test: waived, moderate or high.
Definition and scope
The CLIA regulations define a laboratory as a facility for the “biological, microbiological, serological, chemical, immunohematological, hematological, biophysical, cytological, pathological, or other examination of materials derived from the human body for the purpose of providing information for the diagnosis, prevention, or treatment of any disease or impairment of, or the assessment of the health of, human beings” (42 CFR 493.2, read 2026-11-08). The same section excludes facilities that only collect or prepare specimens, or only serve as a mailing service, without performing testing.
That legal definition is deliberately broad, and it spans disciplines such as histopathology, microbiology and clinical chemistry. For how accreditation and certification frameworks differ, see ISO 15189 vs CLIA.
How oversight works in practice: the complexity ladder
CDC describes three CLIA test complexity categories: waived, moderate and high (CDC CLIA test complexities page, read 2026-11-08). Moderate and high are together called “nonwaived”.
- Waived tests are simple tests with a low risk of an incorrect result. In the regulation, a waived test is one that HHS has determined meets the statutory criteria in section 353(d)(3) of the Public Health Service Act; a nonwaived test is one not found to meet them.
- Moderate complexity includes provider-performed microscopy.
- High complexity is the default for laboratory-developed tests and for commercial tests that a laboratory has modified from the manufacturer’s instructions.
Categorisation uses seven criteria set out in the CLIA regulations, and FDA scores commercially marketed tests during premarket review. CDC notes that the standards for moderate and high complexity differ only in personnel requirements. The test’s category, not the room it sits in, is what the framework classifies; the rapid diagnostic test guide covers one common device class.
Human and animal-health laboratories compared
| Question | Human diagnostic laboratory | Animal-health diagnostic laboratory (US) |
|---|---|---|
| Framework named in the sources | CLIA, 42 CFR Part 493 | USDA APHIS National Animal Health Laboratory Network (NAHLN) |
| How it is organised | Per-test complexity categories (waived, moderate, high) | A “nationally coordinated network and partnership of Federal, State, and university-associated animal health laboratories”, now 66 laboratories, a partnership of APHIS, NIFA and AAVLD |
| Stated purpose | Information for diagnosis, prevention or treatment of disease in humans | “Early detection, rapid response, and appropriate recovery from high-consequence animal diseases” |
| Quality criterion named | Personnel requirements differ by complexity category | AAVLD accreditation, or another public, not-for-profit animal disease diagnostic laboratory with a quality assurance system meeting OIE/ISO 17025 standards and selected by USDA |
Sources: 42 CFR 493.2; CDC CLIA page; USDA APHIS NAHLN “About” page and NAHLN Laboratory Evaluation Policy, all read 2026-11-08. The table sets out what each source says rather than ranking the two systems. For the animal-health side in more depth, see veterinary diagnostics: tests, laboratories and accreditation.
Where it matters for labs, clinics and supply decisions
- Collection sites are not laboratories. A clinic that only draws or swabs and sends specimens out falls outside the federal laboratory definition; the site that performs the testing is the laboratory.
- Modifying a test changes its default category. Because a manufacturer-modified or laboratory-developed test defaults to high complexity, an assay change is a regulatory matter, not only a technical one.
- Central testing is a distinct role. Trials and multi-site programmes often route samples to one laboratory; the clinical trial central laboratory entry explains that arrangement.
Common misunderstandings
Is every site that handles samples a diagnostic laboratory?
No. Under 42 CFR 493.2, preparing or collecting specimens, or mailing them, without performing testing does not make a facility a laboratory.
Does “waived” mean unregulated?
No. Waived is a test category based on an HHS determination under the statute; it describes simple tests with a low risk of an incorrect result, not the absence of rules.
Are moderate and high complexity labs held to different technical standards?
Per CDC, the standards differ only in personnel requirements.
FAQ
What is a diagnostic laboratory?
A facility that examines materials derived from the body to provide information for the diagnosis, prevention or treatment of disease or the assessment of health. The US regulatory wording is in 42 CFR 493.2.
What are the CLIA test categories?
Waived, moderate complexity and high complexity; moderate and high are grouped as nonwaived.
What organises animal diagnostic laboratories in the US?
NAHLN, a network of Federal, State and university-associated laboratories coordinated by USDA APHIS with NIFA and AAVLD. For wider laboratory context, see basics of laboratory work.
Sources
- 42 CFR 493.2, Definitions: law.cornell.edu/cfr/text/42/493.2 (read 2026-11-08)
- CDC, CLIA test complexities: cdc.gov/clia/php/test-complexities (read 2026-11-08)
- USDA APHIS, NAHLN about: aphis.usda.gov/labs/nahln/about (read 2026-11-08)
- USDA APHIS, NAHLN Laboratory Evaluation Policy (PDF): aphis.usda.gov NAHLN Lab Evaluation Policy (read 2026-11-08)
