Method Verification, Validation and Calibration Verification Under CLIA

Last reviewed Oct 2026 · By Sound Lab Consultants CLIA team · Sources: 42 CFR 493.1253, 493.1255; SOM Appendix C (Rev. 236), Interpretive Guidelines §493.1255(b). General information, not legal advice; confirm against the current eCFR and CMS guidance.

Key facts and official sources

• Establishment and verification of performance specifications. Source: 42 CFR 493.1253

• Calibration and calibration verification. Source: 42 CFR 493.1255

• Interpretive guidelines. Source: CMS SOM Appendix C

Before a lab reports patient results on a new nonwaived test system, CLIA requires proof that the system performs as expected in your hands. That proof is either a verification (for unmodified FDA-cleared or approved tests) or an establishment of performance specifications, often called validation (for modified tests and laboratory-developed tests). This page walks through 42 CFR 493.1253 and 493.1255 in plain language.

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What is the difference between method verification and validation?

• Verification (§493.1253(b)(1)) applies to an unmodified, FDA-cleared or FDA-approved test system. The manufacturer already established performance; you confirm it in your lab.

• Establishing performance specifications (§493.1253(b)(2)) applies when the lab modifies an FDA-cleared or approved test, introduces a test system that isn't subject to FDA clearance or approval (including laboratory-developed tests), or uses a test system for which the manufacturer doesn't provide performance specifications.

Under §493.1253(a), test systems a lab was already using before April 24, 2003 are not subject to these requirements. Every system introduced after that date is.

How do you verify an unmodified FDA-cleared test (§493.1253(b)(1))?

Before reporting patient results, the lab must show that it can obtain performance specifications comparable to the manufacturer's for:

• Accuracy, typically by comparing patient or reference samples against a comparative method or materials of known value

• Precision, through repeated testing of the same material within and across runs

• Reportable range, confirming the low-to-high range over which results are reliable

The lab must also verify that the manufacturer's reference intervals (normal values) are appropriate for its patient population.

What do modified tests and LDTs require (§493.1253(b)(2))?

For these systems the lab must establish, before reporting patient results:

• Accuracy and precision

• Analytical sensitivity

• Analytical specificity, including interfering substances

• Reportable range

• Reference intervals

• Any other performance characteristic needed for test performance

The lab must then set calibration and control procedures based on the established specifications (§493.1253(b)(3)) and document everything. For more on LDTs, see our LDT validation page.

What does CLIA require for calibration (§493.1255(a))?

Calibration must be performed and documented following the manufacturer's instructions (including the materials, number of levels and frequency), using the criteria the lab verified or established under §493.1253(b)(3), and again whenever calibration verification fails the lab's acceptable limits (§493.1255(a)).

How often is calibration verification required (§493.1255(b))?

Calibration verification confirms that the system is still calibrated across the reportable range. The lab must:

• Use materials at a minimal (or zero) value, a mid-point value and a maximum value near the upper limit of the reportable range

• Perform it at least once every six months, and whenever:

  • all reagents are changed to a new lot, unless the lab can show the change doesn't affect the reportable range or control values

  • major preventive maintenance is done or critical parts are replaced

  • controls show an unusual trend or shift, or fall outside acceptable limits, and other means can't resolve the problem

  • the manufacturer's instructions or the lab's own criteria call for more frequent verification

CMS interpretive guidelines state that if the lab performs a calibration protocol using 3 or more levels of calibration materials that include a low, mid and high value at least every 6 months, the calibration verification requirement is met (SOM Appendix C, Interpretive Guidelines §493.1255(b), Exception 2, D5439). Routine QC under §493.1256 does not satisfy calibration verification.

What is the difference between AMR and reportable range?

CLIA uses the term reportable range. CAP checklists use analytical measurement range (AMR), the range a method can measure directly without dilution or concentration. Clinically reportable range may extend beyond the AMR when validated dilution procedures are used. CAP-accredited labs should follow the current CAP chemistry checklist for AMR verification frequency and materials.

How do you plan a method verification study?

CLIA doesn't set sample counts or acceptance limits. The lab director defines them in a written verification plan, using manufacturer claims and recognized guidance such as CLSI documents. A good plan states the samples, replicates, statistics, acceptance criteria and who approves the final report. The director signs off before patient testing begins, as part of the director's responsibilities under §493.1407 or §493.1445.

What are common verification survey findings?

• No reference interval verification

• Verification report not reviewed or signed before go-live

• Calibration verification missed after a reagent lot change or major maintenance

• Reportable range on the report not matching the verified range

Related CLIA quality pages

• CLIA quality control requirements

• Instrument validation and verification

• Westgard rules for CLIA quality control

• IQCP 30-day QC

Frequently asked questions

Do we need to verify a second analyzer of the same model?

Yes. Each test system introduced must meet §493.1253 before patient testing. The lab director decides the study scope.

How often is calibration verification required?

At least every six months, and after triggering events such as a complete reagent lot change, major maintenance or unresolved QC shifts (§493.1255(b)(3)).

Does a three-level calibration count as calibration verification?

Yes, if the calibration uses 3 or more levels of calibration materials including a low, mid and high value and is done at least every 6 months (SOM Appendix C, §493.1255(b) Exception 2).

Is method verification required for waived tests?

No. §493.1253 applies to nonwaived testing. Waived tests must be performed according to manufacturer instructions.

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