5.3 Radiopharmaceutical Quality Control
Key Takeaways
- Every preparation needs visual inspection for color, clarity, and particulates before release—except agents that are intentionally particulate (e.g., MAA, sulfur colloid) which have their own appearance criteria
- Radiochemical purity (RCP) distinguishes the desired labeled species from free pertechnetate and hydrolyzed-reduced technetium using ITLC or equivalent methods
- Typical Tc-99m kit RCP limits are often ≥90% or ≥95% desired species—always use the product-specific package insert limit
- Documentation must capture lot numbers, activities, times, QC results, and technologist identity for regulatory and patient-safety traceability
- Reject and do not administer preparations that fail visual checks, RCP limits, breakthrough limits, wrong labeling, or expired dating
Kit preparation is incomplete until quality control clears the product for injection. Domain III pairs visual inspection, radiochemical purity (RCP), documentation, and clear reject criteria to prevent wrong biodistribution, excess dose, and medication errors.
Visual Inspection
View briefly through shielding under adequate light before relying on chromatography.
| Observation | Expectation | If abnormal |
|---|---|---|
| Color | Most Tc-99m agents clear/colorless (some allow pale tint) | Reject unexpected color |
| Clarity | True solutions clear, no haze | Reject unintended cloudiness |
| Particulates | None in solutions | Reject fibers, precipitates, foreign matter |
| Intentional particles | MAA, sulfur colloid: uniform suspension, no large clumps | Reject clumped/aggregated product |
| Integrity | Intact vial/septum, plausible volume | Reject damaged containers |
Visual failure alone is enough to stop—good ITLC does not salvage a dirty vial. Looking normal also does not prove RCP; visual checks are necessary but not sufficient.
Radiochemical Purity and ITLC
Radiochemical purity is the fraction of total radioactivity in the desired chemical form. For Tc-99m kits, classic impurities are:
- Free pertechnetate (TcO₄⁻) — unbound oxidized Tc; often localizes in stomach, thyroid, salivary glands.
- Hydrolyzed-reduced Tc (HR-Tc) — colloidal reduced impurity; often liver, spleen, marrow.
ITLC (or paper chromatography) uses kit-specific strips and solvents to separate species. Conceptual two-system model:
| Generic system | Often migrates | Often at origin |
|---|---|---|
| System A (e.g., saline/acetone-type, kit-dependent) | Free TcO₄⁻ in many methods | Bound complex + HR-Tc |
| System B (kit-specific) | Bound complex (± free tech) | HR-Tc |
Count strip sections (well counter, dose calibrator, or scanner per SOP):
[ %\ \text{desired} = 100% - %\text{free TcO}_4^- - %\text{HR-Tc} ]
Exact solvents and cut lines are product-method specific. The exam cares that you know what free tech and HR-Tc are and that RCP = desired fraction.
Worked example 1 — RCP
Impurities: 4% free TcO₄⁻ + 3% HR-Tc → desired 93%. Passes a ≥90% limit; fails ≥95%.
Worked example 2 — Image clue
Unexpected stomach/thyroid on a bone scan suggests free pertechnetate—why RCP is done before imaging, not after a ruined study.
Typical Purity Limits and Purity Types
| Product / test | Common teaching limit |
|---|---|
| Many Tc-99m kits | ≥90% desired species |
| Stricter Tc-99m kits | ≥95% (use the insert) |
| Mo-99 in eluate | ≤0.15 μCi Mo / mCi Tc at admin |
| Al³⁺ | ≤10 μg/mL |
| I-131, In-111, others | Product-specific |
| Purity type | Question | Example |
|---|---|---|
| Radiochemical | Correct chemical form? | ITLC free TcO₄⁻ / HR-Tc |
| Radionuclidic | Correct radionuclide? | Mo-99 breakthrough |
| Chemical | Nonradioactive impurities OK? | Al³⁺ test |
| Microbial | Sterile process maintained? | Asepsis / sterility programs |
Do not confuse radiochemical (wrong form of Tc) with radionuclidic (wrong nuclide such as Mo-99).
Documentation and Labeling
Trace every dose from patient → kit lot → generator elution when applicable. Record:
- Product name/route, kit lot, generator/eluate ID if used
- Preparation activity, volume, concentration, time, expiration
- QC results: visual, RCP %, Mo-99 ratio, Al³⁺ as required
- Technologist ID / instrument ID per policy
- Patient syringe: prescribed vs assayed activity, assay time, volume
Syringe labels must stay legible: drug, activity, time, patient identifiers. A mislabeled syringe is a critical event even if chemistry was perfect. Keep paper or electronic records long enough to satisfy license, state, and institutional retention rules.
When to Reject
Do not administer if any apply:
- Failed visual inspection (wrong color, unexpected particles, clumped MAA).
- RCP below insert limit.
- Mo-99 > 0.15 μCi/mCi Tc at admin time.
- Al³⁺ > 10 μg/mL (or other chemical limits).
- Expired kit or post-reconstitution dating exceeded.
- Wrong product/lot or unresolvable labeling error.
- Activity/volume outside allowed range when SOP requires discard.
- Compromised sterility or temperature abuse per policy.
Worked example 3 — Reject
MDP looks clear; ITLC 6% free + 5% HR-Tc = 89% desired; limit ≥90%. Reject, remake, investigate (old eluate, excess activity, air), document—do not inject hoping the scan will be fine.
Worked example 4 — Release
Sestamibi: visual OK; RCP 96% (limit ≥90%); within activity/volume limits; within dating; labels complete → release.
Chain of Custody for Quality
Generator QC (assay, Mo-99, Al³⁺) → kit within limits → visual + RCP → assayed labeled dose → inject before expiration. Break any link → stop.
Match failure to test: thyroid/stomach → free TcO₄⁻; liver/spleen on non-colloid study → HR-Tc; held eluate with rising Mo ratio → breakthrough; pediatric lung issues → particle number, not mCi alone.
If QC fails, quarantine the vial, label it not for use, notify the supervising pharmacist/authorized user or RSO per SOP, and prepare a replacement only after the cause is addressed when time allows. Never “top off” a failed kit with more pertechnetate hoping purity will improve without a validated procedure.
Exam hooks: visual first; ITLC for free TcO₄⁻ and HR-Tc; limits often ≥90–95%; full documentation; written limit failed → reject.
On Tc-99m kit quality control, free pertechnetate (TcO₄⁻) and hydrolyzed-reduced technetium (HR-Tc) are primarily examples of failures of:
ITLC analysis of a Tc-99m kit shows 3% free pertechnetate and 2% hydrolyzed-reduced Tc. The package insert requires ≥95% radiochemical purity. What is the correct action?
Which situation requires rejection of a radiopharmaceutical preparation?