Root cause analysis after a false negative TB result
A false negative tuberculosis result can delay treatment, prolong transmission, and create false reassurance for patients and clinical teams. It can also reveal weaknesses in specimen collection, testing procedures, equipment, staff competency, reporting, or communication. A root cause analysis (RCA) helps the laboratory move beyond blaming an individual and identify the conditions that allowed the inaccurate result to occur.
The purpose of an RCA is to understand what happened, why it happened, and how the laboratory can prevent recurrence. The investigation should be timely, impartial, evidence-based, and proportionate to the potential harm. It should include laboratory staff and, where appropriate, clinicians, specimen collection teams, quality officers, and biosafety personnel.
A useful investigation distinguishes the immediate error from the deeper system failure. For example, a missed internal control may explain why a molecular test was invalid, while inadequate training, unclear review responsibilities, or excessive workload may explain why the invalid result was released or not repeated.
Protect the patient and contain the event
The first priority is to manage the clinical and public health risk. Notify the laboratory director or quality manager, inform the treating team through the approved communication pathway, and determine whether the patient needs repeat testing or urgent clinical review. The response should follow local policy and national tuberculosis guidelines, especially where multidrug-resistant TB is possible.
Secure the relevant records and materials before routine disposal. These may include the original specimen, residual sample, extraction batch, cartridges or test strips, worksheets, instrument files, quality control results, temperature records, and the final report. If the specimen is still suitable, preserve it under appropriate conditions for retesting or referral to a higher-level laboratory.
Consider whether other patients may be affected. A false negative linked to a reagent lot, instrument fault, contamination of workflow areas, power interruption, or reporting configuration may involve a batch of results rather than one sample. Review tests performed during the relevant period and place affected reports under controlled review while the investigation proceeds.
Define the event and collect evidence
Begin with a precise problem statement. “A patient with clinically suspected pulmonary TB received a negative molecular result, and repeat testing later detected Mycobacterium tuberculosis” is more useful than “the laboratory made a mistake.” Record the test method, date and time, specimen type, sample condition, result, clinical context, repeat result, and how the discrepancy was identified.
Build a simple timeline from collection to reporting. Include who collected and transported the specimen, when it arrived, how it was accessioned, where it was stored, when processing began, which operator performed each step, and when the result was reviewed and released. Compare actual events with the approved standard operating procedure rather than relying on memory alone.
Evidence should come from several sources. Review worksheets, electronic logs, instrument audit trails, reagent and control records, maintenance reports, environmental logs, stock records, staff schedules, and competency assessments. Interview personnel individually and use neutral prompts such as “What happened next?” and “What made that step difficult?” This approach produces more reliable information than asking who caused the failure.
Documentation is especially important because it preserves the sequence of events and supports trend analysis. The GLI resource on documentation guidance explains how controlled records, forms, and procedures support consistent laboratory practice.
Examine the full testing pathway
A negative TB result may arise from a problem before testing, during testing, or after the analytical process. Pre-analytical factors include an inadequate volume, saliva rather than sputum, poor collection instructions, delayed transport, leakage, incorrect labeling, unsuitable storage, or a specimen from the wrong patient. The laboratory should also examine whether the specimen was representative of the disease site.
Analytical causes can include incorrect specimen processing, insufficient mixing, pipetting errors, expired or improperly stored reagents, cartridge damage, inhibited amplification, instrument malfunction, failed internal controls, or inappropriate interpretation of a weak signal. In smear microscopy, low bacillary load, poor smear preparation, staining defects, dirty optics, or inadequate examination time may contribute.
Post-analytical causes include transcription errors, incorrect result selection in the laboratory information system, failure to recognize an invalid result, incomplete review, delayed escalation, or communication of a preliminary result as final. A technically correct test can still cause harm if its limitations are not understood or the result is transmitted inaccurately.
Use a process map or fishbone diagram to organize possible causes across people, methods, materials, machines, environment, and management. The aim is to test each possibility against evidence. A plausible explanation is not a root cause until records, repeat testing, observation, or another reliable source supports it.
| Investigation area | Evidence to review | Possible contributing cause | Useful verification |
|---|---|---|---|
| Specimen collection | Collection records, rejection log, patient instructions | Poor-quality or insufficient specimen | Repeat collection review and staff observation |
| Transport and storage | Receipt time, temperature, transport log | Delay or unsuitable storage | Compare with procedure and transport requirements |
| Testing process | Worksheets, controls, instrument files | Processing or pipetting deviation | Retest, observe workflow, inspect audit trail |
| Reagents and equipment | Lot records, expiry dates, maintenance logs | Failed reagent or instrument performance | Quality control review and service assessment |
| Result review | Electronic record, authorization trail | Misinterpretation or transcription error | Independent report comparison |
| Quality system | SOPs, training, audits, workload data | Weak oversight or unclear responsibility | Document review and staff interviews |
Use a structured method to identify root causes
The five-whys method is useful when applied carefully. Ask why the false negative occurred, then continue asking why each answer was possible. For example, a negative result was released because the control failure was not recognized; the failure was not recognized because the review screen did not display the control status clearly; the screen was not checked because the review procedure was incomplete; and the procedure was incomplete because it had not been revised after the instrument upgrade.
Avoid stopping at “staff did not follow the SOP.” That statement describes an action, not necessarily the cause. Ask whether the SOP was available at the workstation, written clearly, compatible with the instrument, reinforced through training, and realistic under current workload. Also examine whether supervision, competency assessment, staffing levels, and supply continuity supported correct performance.
A root cause should explain the event and point toward an effective control. If replacing one staff member would not prevent recurrence, the investigation has probably stopped too early. Several contributing factors may exist, such as poor specimen quality combined with a weak rejection policy and inadequate clinician communication. Record these relationships instead of forcing the event into a single cause.
Design corrective and preventive action
Corrective action addresses the specific event. It may include repeat testing, amended reporting, clinician notification, equipment repair, reagent quarantine, staff retraining, or referral of specimens to a reference laboratory. Each action should have an owner, due date, required resources, and a defined completion record.
Preventive action changes the system so that the same failure is less likely. Examples include revising collection instructions, adding a specimen acceptance checklist, introducing independent review of critical or unexpected results, strengthening internal quality control rules, improving instrument maintenance, or configuring electronic alerts for invalid runs.
Actions should match the risk and the verified cause. Retraining alone is weak when the real issue is an unclear workflow, unavailable supplies, excessive workload, or a poorly designed form. A practical quality management system connects procedures, personnel, equipment, assessment, and continual improvement. Laboratories building this foundation can use the QMS implementation guide to organize responsibilities and controls across the testing pathway.
Verify effectiveness and share the learning
An action is complete only when its effectiveness has been checked. Define a measurable indicator, such as the percentage of specimens meeting acceptance criteria, the frequency of invalid runs, the proportion of critical results independently reviewed, or the number of documentation errors per month. Compare performance before and after the intervention over a suitable period.
Repeat observation or competency assessment when the change involves staff practice. Perform targeted internal audits when the issue involves documentation, equipment, or reporting. If a new checklist is introduced, verify that it is being used correctly and that it catches the intended problem without creating unnecessary delays.
Share lessons with relevant staff in a blame-free format. Discuss the event during a quality meeting, document the decision and assigned actions, and update affected procedures or training materials under document control. Protect patient confidentiality while ensuring that the learning reaches specimen collectors, bench staff, supervisors, clinicians, and managers who influence the process.
A well-run investigation should produce a clear record containing the event description, risk assessment, evidence reviewed, identified causes, immediate containment, corrective and preventive actions, responsible persons, deadlines, and effectiveness results. This record can support future audits and help detect recurring patterns across methods, sites, or specimen types.
Make the response part of routine quality improvement
Laboratories should establish a consistent pathway for investigating discordant, unexpected, invalid, or amended TB results. Include criteria for escalation, responsibilities for notification, timelines for review, and methods for protecting specimens and electronic data. Regularly trend false negative suspicions alongside rejected specimens, quality control failures, equipment downtime, and reporting amendments.
Use these practices to strengthen the laboratory’s response:
- Treat every suspected false negative as a patient-safety and public-health event, not merely a technical discrepancy.
- Review the complete pre-analytical, analytical, and post-analytical pathway using documented evidence.
- Separate human actions from system conditions that shaped those actions.
- Assign corrective actions with owners, deadlines, measurable indicators, and effectiveness checks.
- Share verified lessons through controlled procedures, competency activities, and quality meetings.
The value of root cause analysis is realized when findings lead to safer decisions and more reliable testing. Use the investigation record to improve the local quality management system, monitor whether controls work in practice, and escalate unresolved risks through the laboratory and public health leadership structure. Begin with the next suspected false negative, preserve the evidence, involve the right people, and turn the event into a documented improvement in TB diagnosis.