Choosing Reliable TB Quality Control Materials
Commercially available tuberculosis quality control materials can help laboratories monitor testing accuracy, identify technical problems, and support a functioning quality management system. They may be supplied as dried or liquid preparations, preserved organisms, molecular control panels, or materials designed for smear microscopy, culture, identification, or drug susceptibility testing.
The purchasing decision should be based on more than price and a product catalogue description. A material that performs well for one assay may be unsuitable for another, while a product that is technically excellent may be impractical if it requires a cold chain the laboratory cannot maintain. Evaluation should therefore connect the material’s scientific characteristics with the laboratory’s methods, risks, staffing, infrastructure, and quality objectives.
A structured review also creates useful evidence for procurement, verification, inventory control, and continual improvement. The goal is to select a control that produces meaningful information about the testing process without introducing avoidable biosafety, interpretation, or supply problems.
Define the intended use
Begin by stating what the quality control material must demonstrate. Internal quality control for nucleic acid amplification testing has different requirements from a control used for smear staining, culture recovery, species identification, or phenotypic drug susceptibility testing. The laboratory should identify the exact platform, reagent system, specimen type, target organism, drug panel, and reporting decision involved.
A positive control may show that an assay can detect a target, but it may not reveal extraction failure, inhibition, contamination, or an incorrect specimen preparation step. A negative control can help identify contamination, yet it does not establish that the assay can detect low-level tuberculosis complex material. Some programs therefore need multiple control levels, including a weak-positive concentration near the clinical or analytical decision point.
The intended use should also specify whether the material is for daily internal monitoring, new lot verification, staff competency assessment, troubleshooting, method comparison, or external quality assessment preparation. A product designed for proficiency testing may not be suitable for routine use if its concentration, format, or distribution schedule does not match the laboratory’s workflow.
Check scientific performance
Review the manufacturer’s evidence for identity, concentration, analyte composition, homogeneity, and expected results. The documentation should explain how the material was characterized and whether assigned values are based on a reference method, consensus results, or a manufacturer-defined target. For antimicrobial resistance controls, the expected susceptible or resistant phenotype must be clearly linked to the specific drug and method.
Analytical sensitivity is especially important for TB molecular controls. A high-concentration positive control may produce reassuring results while failing to challenge the lower detection range of the assay. Ask whether the material includes clinically relevant concentrations and whether the expected result is qualitative, semi-quantitative, or quantitative. If the control contains inactivated material, confirm that inactivation does not alter the assay target or the behavior of the material during extraction.
Commutability should receive careful attention. A material is more useful when it behaves like a patient specimen throughout the testing process. A purified nucleic acid control may verify amplification but cannot assess specimen lysis, extraction, purification, or inhibition. Similarly, a nonclinical matrix may produce different smear, culture, or molecular performance from sputum. The closer the control is to routine specimens, the more meaningful the result is for the full workflow.
For laboratories comparing products, the user instructions provide useful context on how quality activities and supporting materials can be organized within a phased improvement process.
Examine stability and safety
Stability claims should cover the complete period of intended use, including transport, storage, opening, repeated handling, and use after reconstitution. Look for real-time stability data rather than relying only on accelerated studies. The label should state storage temperature, light protection, freeze-thaw limitations, expiry date, and the period for which a reconstituted or opened vial remains acceptable.
Transport conditions are part of product performance. A control that arrives warm, damaged, leaking, or outside its temperature range may no longer have the assigned characteristics. Laboratories should establish an incoming inspection process that records shipment condition, lot number, expiry, temperature indicators where available, and any deviation from specifications.
Biosafety information must be explicit. “Inactivated” does not automatically mean that every risk has been eliminated under every handling condition. The product insert should describe the organism or material present, the inactivation method where relevant, residual risks, recommended containment, spill response, and waste disposal. Laboratories should involve their biosafety officer or responsible technical lead before accepting materials that contain viable organisms or hazardous substances.
Packaging also matters. Vials should be clearly labelled, tamper evident, resistant to leakage, and easy to distinguish from clinical specimens. A product that creates a realistic risk of mix-up or requires complicated reconstitution may undermine the quality system even if its analytical properties are strong.
Verify supplier and lot control
A dependable supplier should provide a complete technical file, certificate of analysis, safety information, instructions for use, and a clear process for reporting problems. The certificate should identify the lot, assigned values or expected results, production date, expiry date, storage requirements, and acceptance criteria. Vague statements such as “suitable for laboratory quality control” are not enough to support verification.
Ask how the supplier controls manufacturing consistency. Important questions include whether each lot is tested independently, how homogeneity is assessed, what release criteria are applied, and whether changes in raw materials or production methods trigger notification. Lot-to-lot variation can create false trends that look like assay deterioration or operator error.
Customer support is also part of quality. Laboratories need timely answers when a control gives an unexpected result, when a shipment is delayed, or when a product becomes unavailable. A supplier should have a documented complaint and recall process, retain production records, and communicate corrective actions. Availability over the expected program period may be more valuable than a lower initial purchase price.
Where possible, obtain a sample or small starter pack for local verification. Test it using the routine method, operators, equipment, and environmental conditions. Compare results with the manufacturer’s assigned values and with an established control if one is available. Do not release a new commercial lot for routine use solely because the previous lot was satisfactory.
Compare options against laboratory needs
A clear comparison helps prevent procurement decisions based on a single attractive feature. The following criteria can be scored using a simple scale, such as acceptable, conditional, or unacceptable. A weighted score may be useful when several products meet the minimum technical requirements.
| Evaluation area | Evidence to review | Key decision |
|---|---|---|
| Intended use | Assay, specimen type, target, and control level | Does it challenge the complete testing process? |
| Accuracy and assigned value | Reference method, consensus data, certificate of analysis | Are expected results credible and unambiguous? |
| Matrix and commutability | Specimen-like composition and extraction behavior | Does it behave like routine patient material? |
| Stability | Shelf life, transport data, opened-vial and reconstitution limits | Can the laboratory maintain performance in its conditions? |
| Biosafety | Viability status, handling instructions, waste requirements | Can staff use it safely with available controls? |
| Lot consistency | Homogeneity testing and lot-release procedures | Will results remain comparable over time? |
| Logistics | Packaging, cold chain, delivery time, minimum order | Can supply be maintained without avoidable interruptions? |
| Cost and workload | Purchase price, shipping, preparation, waste, repeat testing | Is the total cost compatible with the program? |
| Documentation and support | Instructions, certificates, complaint response, recall system | Can the laboratory defend and troubleshoot its use? |
Cost should include more than the price per vial. Include freight, customs, cold storage, consumables, reconstitution time, unusable volume, disposal, and repeat testing after failed verification. A less expensive material may cost more if it expires before use or requires equipment that the laboratory does not possess.
The final choice should document both strengths and limitations. For example, a synthetic molecular control may be highly stable and safe but unable to assess extraction, while a whole-organism control may provide broader process coverage but require more demanding biosafety arrangements. A transparent decision record makes these trade-offs visible to management and assessors.
Integrate the control into routine monitoring
After selection, define how the material will be used. The quality control procedure should specify frequency, control level, placement within a run, acceptable results, actions for failure, and responsibilities for review. The laboratory should avoid treating control testing as a box-ticking exercise; results need to inform decisions about releasing patient results, repeating runs, investigating trends, or stopping testing.
Control charts can help identify gradual shifts, increasing variability, or sudden changes after a reagent, instrument, operator, or environmental change. For qualitative TB assays, laboratories can still record the expected and observed result, cycle threshold or signal where relevant, invalid rates, and associated run conditions. For culture and susceptibility testing, review may include recovery, contamination, growth characteristics, and agreement with expected resistance patterns.
The GLI Quality Tool’s phase checklists can help laboratories connect control-material selection with broader requirements for equipment, documents, personnel, assessment, and continual improvement. This prevents quality control from becoming an isolated activity managed only by the bench technologist.
Document verification and review
Verification records should identify the product, manufacturer, lot, expiry, storage conditions, method, operators, number of runs, expected results, observed results, deviations, and approval decision. Retain the certificate of analysis and relevant instructions with the record. If the product is accepted with restrictions, state those restrictions clearly and communicate them to all users.
Review the material periodically and whenever there is a significant change. Triggers include a new assay platform, revised testing algorithm, repeated control failure, supplier change, transport excursion, new biosafety information, or evidence that the material no longer reflects routine specimens. A control may remain within its expiry date while becoming less useful because the laboratory’s method or clinical needs have changed.
Practical selection priorities
- Match the material to the complete testing process, not just the final detection step.
- Require evidence for assigned values, homogeneity, stability, and lot-to-lot consistency.
- Confirm storage, transport, biosafety, and waste requirements before purchase.
- Verify every new lot under routine laboratory conditions before release.
- Record control results, investigate trends, and review the product when methods or risks change.
A well-chosen commercial control material gives the laboratory credible evidence that its TB testing system is working as intended. Evaluate products systematically, retain the evidence behind the decision, and use routine results to drive corrective action and continual improvement. This approach turns procurement into a practical part of laboratory quality management rather than a one-time purchasing decision.