Radionuclidic Identity Test

This glossary term is part of the SG Systems Global regulatory & operations guide library.

Updated January 2026 • 21 CFR Part 212 PET drug cGMP, radionuclide verification, identity acceptance criteria, time-anchored measurements, release gating, method governance, deviations and CAPA, audit-ready records • Primarily PET & radiopharmaceutical operations (cyclotron sites, radiochemistry labs, nuclear pharmacies, hospital PET production)

Radionuclidic Identity Test is the controlled verification that the radionuclide in a PET drug product is the radionuclide you intended to produce. It is the “prove it” step for radionuclide identity—separate from chemical identity and separate from purity. In an environment governed by 21 CFR Part 212, identity is not assumed based on the schedule, the target used, or the operator’s expectation. It is confirmed using defined methods, defined timing, and defined acceptance criteria that are recorded and reviewable.

The business value is blunt: the wrong radionuclide is not a “minor defect.” It is a patient safety risk, a regulatory event, and a credibility collapse for your operation. The compliance value is equally blunt: if you can’t show how identity was verified, when it was verified, what the acceptance criteria were, and how results drive release decisions, you do not control identity—you narrate it after the fact.

Tell it like it is: identity failures are rare, but they are catastrophic when they happen. The bigger risk is not frequent wrong-isotope production; it’s casual “we know what it is” culture. That culture creeps in when time pressure is high and the workflow treats identity testing as optional. A controlled identity program prevents that: tie the test to a lot or dose ID, anchor it to a defined time reference (often EOS or calibration time), govern the method and instrument, and hard-gate release actions when identity is unknown or inconsistent.

“In radiopharma, identity is not what you meant to make. Identity is what you can prove you made.”

1) What a radionuclidic identity test is (and what it is not)

A radionuclidic identity test is a documented verification that the radionuclide present matches the intended radionuclide. It is a controlled test or method-driven check with defined acceptance criteria and defined timing. The identity result is tied to the lot/dose identity and becomes part of the release rationale.

It is not a scheduling assumption (“we ran F-18 today”). It is not a proxy for purity (“it looks clean”). And it is not optional because the run is late. In PET operations, the correct approach is harsh: if identity is not confirmed, the product is not eligible for use.

2) Why identity verification matters in PET drugs

Radiopharmaceutical identity is foundational. The wrong radionuclide can change radiation dose profiles and clinical performance. From a quality standpoint, if identity is uncertain, everything downstream is compromised: purity assessment, activity statements, time windows, and labeling become unreliable.

Tell it like it is: identity verification is one of the few controls that is both simple and absolute. Either you can prove the intended radionuclide is present, or you cannot. A mature program treats identity as a hard gate that cannot be negotiated away by schedule pressure.

3) Identity vs purity vs radiochemical purity (stop mixing the words)

These concepts are distinct and must be controlled distinctly:

• Radionuclidic identity confirms the intended radionuclide is present.
• Radionuclidic purity limits unintended radionuclides (see Radionuclidic Purity Limit).
• Radiochemical purity addresses chemical form and labeling chemistry, not nuclide mix.

Tell it like it is: mixing these terms in SOPs produces weak controls. You can pass identity and still fail purity. You can pass purity and still fail radiochemical purity. Keep them separate in test names, acceptance criteria, and failure response workflows.

4) Acceptance criteria: what “passes” and what fails

Identity acceptance criteria must be explicit. That means:

• what is measured (the identity signature your method detects),
• what range is acceptable (numeric boundaries, not “looks right”),
• what constitutes failure (mismatch, ambiguity, insufficient confidence),
• what constitutes invalid (instrument issue, unsuitable run, sample error),
• what actions follow (hold, retest under rules, investigation, disposal).

Tell it like it is: vague acceptance criteria are a hidden loophole. Under time pressure, vague criteria become “close enough.” Close enough is unacceptable for identity. Make criteria objective and enforceable.

5) Method options: how identity is demonstrated

Identity can be demonstrated using different method approaches depending on product and validated practice. What matters is method governance and suitability. Method governance should define:

• instrument and configuration (what device, what setup, what settings),
• standard/reference used for comparison where applicable,
• calculation rules and reporting conventions,
• system suitability checks and what invalidates a run,
• review requirements and approval authority.

Tell it like it is: method variability is identity risk. If identity depends on who is working, you don’t have identity control. Standardize the method, lock it in procedures, and keep the result format consistent so reviews are fast and reliable.

6) Timing and anchors: EOS, calibration time, and time-dependent signatures

Identity verification happens at a time, and time matters. Your record must capture:

• when the identity test was performed (timestamp),
• what it is anchored to (often EOS or calibration time),
• whether any correction rules apply (document basis clearly),
• how this timing relates to use window (see BUT).

Tell it like it is: if timing isn’t captured, identity comparisons can become ambiguous. Time anchors also make audits easier: you can show identity was verified before release and within the controlled workflow.

7) Sampling and unit-of-use: what is tested and how it links to doses

Identity testing must link to what will actually be used. Sampling strategy should define:

• sample point (post-synthesis, post-purification, final product),
• sample ID tied to the lot/dose identity,
• how dose-level units inherit identity from lot-level results,
• what triggers additional identity checks (process interruptions, abnormal conditions).

Tell it like it is: if sample identity is weak, your identity result is weak. Sample IDs must be controlled, not scribbled on vials. Link sample capture to the system of record so you can prove chain-of-custody from sample to result to released dose.

8) Release gates: where identity is enforced in workflow

Identity must be enforced as a workflow gate. At minimum:

• release gate blocks release if identity is missing, invalid, or failing.
• pick/dispatch gate blocks movement if identity is unresolved or on hold.
• conditional release logic must still require identity (pending sterility does not bypass identity).

Tell it like it is: the fastest way identity programs fail is “we’ll verify later.” Later becomes never, and then the organization has no proof identity was known at the decision point. Gate it early, gate it automatically, and keep it non-negotiable.

9) Equipment control: ensuring measurement systems are credible

An identity test is only as credible as the equipment behind it. Controls should include:

• instrument ID captured with each result,
• calibration/verification status and suitability checks,
• lockouts when equipment is out of tolerance,
• maintenance records and change history,
• operator authorization to prevent untrained use.

Tell it like it is: if an instrument is overdue or unverified, identity results become defendable only in conversation, not in records. Put equipment control in the same discipline as any GMP measurement system.

10) Review and approval: who signs off and what they must check

Review should be efficient and standardized. Review expectations should define what must be checked:

• correct method and version used,
• system suitability passed,
• sample identity matches the lot/dose,
• acceptance criteria clearly met,
• time stamp and anchor captured,
• any anomalies flagged and dispositioned.

Tell it like it is: reviews fail when reviewers need to “interpret” results. Make results structured, comparable, and rule-based so review becomes confirmation, not debate.

11) Exceptions and invalid results: retest rules and containment

Identity testing will occasionally produce invalid runs due to instrument issues or sample handling errors. That’s normal. What matters is controlled retest rules. Define:

• what qualifies as invalid vs failing,
• who can authorize retest and under what conditions,
• how sample identity is preserved during retest,
• what happens while unresolved (hold/disposition gate),
• how repeated invalids are handled (investigation trigger).

Tell it like it is: if retest is used as a way to “get a pass,” your program is corrupt. Retest is for invalidations and controlled confirmatory steps, not for shopping for outcomes.

12) OOS and OOT posture: when identity doesn’t match

If identity fails, the response must be immediate and controlled:

• containment (block release, stop movement, prevent dispatch),
• deviation and investigation initiation,
• scope assessment (what else might be affected: same target, same day, same equipment),
• disposition rules (reject, quarantine, controlled disposal),
• CAPA when systemic weaknesses exist.

Tell it like it is: an identity failure is not a “minor deviation.” It is a severe signal that something in control logic, equipment, or workflow discipline failed. Treat it accordingly.

13) Trending and drift signals: identity checks as process telemetry

Identity results are often “pass/fail,” but the underlying measurements can still provide drift signals. Use them as telemetry:

• track invalid run rates by instrument and shift,
• track near-boundary results if your method supports it,
• correlate anomalies with equipment events and interventions,
• trend identity test completion time vs release time to detect schedule pressure risks.

Tell it like it is: when schedule pressure rises, identity discipline is often the first thing teams try to weaken. Trend completion timing and block “release before identity” behaviors.

14) Data integrity: audit trails, edits, and “no reconstruction” posture

Identity is safety-critical. Credibility requires:

• unique user identities (no shared logins),
• instrument IDs and method versions recorded,
• audit trails for edits with reason-for-change,
• controlled permissions for approving/invalidating results,
• no backdating or quiet record cleanup under time pressure.

Tell it like it is: if identity records can be manipulated, your entire release record credibility is compromised. Use strict permissions and audit trails so identity evidence is trustworthy.

15) Records package: what you must be able to show on demand

Inspection readiness means you can produce identity evidence quickly for any lot or dose:

• method reference and version,
• acceptance criteria and specification linkage,
• raw and calculated results with time stamps and anchors,
• instrument status evidence (suitability, verification),
• review/approval records and associated release decisions,
• exceptions (invalid runs, retests, investigations) with closure evidence.

Tell it like it is: if you can’t show the method and time anchor, the result is not defendable. A number without context is not evidence.

16) KPIs: proving identity verification is reliable

KPIs keep the program honest and detect drift in discipline:

Tell it like it is: if on-time identity completion drops, your organization is drifting into “release first, prove later” culture. Fix it immediately with gating and staffing—not with reminders.

17) Copy/paste readiness scorecard

Use this to evaluate whether your radionuclidic identity program is defensible.

18) Failure patterns: how identity programs collapse in real life

• Assumption culture. “We know what it is.” Fix: hard gates and mandatory identity capture.
• Vague criteria. “Looks right” decisions. Fix: objective acceptance criteria.
• Method drift. Analysts vary execution. Fix: method governance and suitability checks.
• Release-first behavior. Product moves before identity is confirmed. Fix: workflow gating at release/pick/ship.
• Retest roulette. Retest until pass. Fix: controlled retest rules and investigations.
• Weak sample control. Samples not linked to lots. Fix: barcode IDs and chain-of-custody.
• Record cleanup. Quiet edits after the fact. Fix: audit trails and permission gating.

Tell it like it is: identity control collapses when speed is prioritized over proof. The fix is structural—gates, method discipline, and data integrity—not motivational speeches.

19) Change control: method changes and acceptance criteria changes

Changing identity methods or criteria is high impact. Govern changes with:

• change request with rationale and risk assessment,
• comparability evidence when methods change,
• approval workflow and effective-date governance,
• training updates so execution remains consistent,
• version linkage so historical results remain interpretable.

Tell it like it is: uncontrolled method changes destroy trend credibility and open audit vulnerabilities. Keep versions explicit and traceable.

20) Training and competency: making identity non-negotiable

Identity discipline must survive schedule pressure. Training should be role-based:

• operators: what actions are blocked without identity confirmation,
• analysts: method execution, suitability checks, and reporting discipline,
• QA/reviewers: what must be checked and what triggers holds/investigations,
• dispatch/pickers: scan-first identity verification and hold enforcement.

Tell it like it is: if only one expert understands identity logic, the program is fragile. Make identity “boring and automatic” through workflow design, then train people to trust the gates rather than bypass them.

21) How this maps to V5 by SG Systems Global

V5 supports radionuclidic identity testing by linking governed methods, time anchors, release rules, and investigations into one controlled system:

• V5 MES captures execution anchors (e.g., EOS), links lots/doses to process context, and enforces readiness gates so product cannot progress when identity is unresolved.
• V5 QMS governs specifications and acceptance criteria, manages approvals and holds, and triggers deviation investigations and CAPA when identity results are failing or repeatedly invalid.
• V5 WMS enforces disposition-based movement and shipping blocks so units cannot be picked or shipped without confirmed identity and eligible status.
• V5 Solution Overview explains how MES + QMS + WMS operate as one control layer so identity verification is not trapped in a lab silo.
• V5 Connect API supports integration to LIMS and instrument pipelines so identity results, method metadata, and state transitions can synchronize automatically and trigger workflow actions in real time.

This enables a practical outcome: identity evidence is captured once, tied to the correct lot/dose, reviewed quickly, and enforced automatically in release and shipping workflows—without relying on manual policing.

22) Extended FAQ

Q1. Is radionuclidic identity testing the same as radionuclidic purity?
No. Identity confirms the intended radionuclide is present. Purity limits how much unintended radionuclide content is present. You can pass identity and still fail purity.

Q2. What is the most important control for identity verification?
A hard release gate: product cannot be released, picked, or shipped without confirmed identity. Warnings are not enough under time pressure.

Q3. What should happen if identity is unclear or invalid?
The lot should be held, retest should occur only under controlled rules, and repeated invalids should trigger investigation. Identity uncertainty is not a “minor issue.”

Q4. Why do identity programs fail operationally?
Because teams assume identity based on schedule and skip verification when late. If identity can be skipped, it will be skipped. Gates prevent that behavior.

Q5. What must records show to be inspection-ready?
Method and version, acceptance criteria, instrument identity/status, time anchor, raw and calculated result, reviewer approval, and any exceptions/investigations—linked to the lot/dose identity.

Related Reading (keep it practical)
Identity and purity must be treated as distinct controls: confirm radionuclide identity, then enforce impurity boundaries using Radionuclidic Purity Limit. Anchor identity evidence to End-of-Synthesis Time and apply time gating via Beyond-Use Time. When conditional distribution exists, identity must remain a non-negotiable prerequisite even under Sterility Release Pending workflows.