19.2 Quality Control, Root-Cause Analysis, and POCT

19.2 Quality Control, Root-Cause Analysis, and POCT

Quick Answer: Quality is preanalytic, analytic, and postanalytic. After a missed organism or QC failure, hold related patient results and find the system cause with 5 whys or a fishbone—do not stop at blaming one technologist. Media QC is sterility, growth promotion, and selectivity; stains, reagents, AST, and equipment need in-control QC the day of use. Failed QC means no patient release for that method. Rapid flu, strep, and COVID POCT still require operator competency and QC; waived is not "no QC."

Official outline IV.B Quality Assessment/Troubleshooting (guideline 2025-09-25) is M-tested laboratory operations: the three testing phases, root-cause analysis, quality control, and point-of-care testing. Proficiency testing, competency, and accreditation are 19.3. IV.F Laboratory Administration is SM-only.

Preanalytic, analytic, and postanalytic quality

A missed Shigella can be a transport delay (preanalytic), a failed selective agar (analytic), or a report that never reached infection control (postanalytic). Quality assessment looks at all three phases. Reviewing only the MALDI log after a wrong-patient report is incomplete quality.

Correlation is the exam skill. If Gram-stain QC fails, hold patient stains. If Campylobacter agar fails growth promotion, do not report "no Campylobacter." If an incubator ran at 31 °C overnight, do not autoverify negative cultures from that chamber.

Root-cause analysis after a miss or a QC fail

Root-cause analysis (RCA) asks why the system allowed the event, not only who touched the plate. Two tools appear on exams.

5 whys. Keep asking why until the answer is a process that can be redesigned. Example: Campylobacter missed on stool culture. Why? No growth on Campy agar. Why? The atmosphere was ambient air. Why? The jar catalyst was expired. Why? There was no scheduled check. Why? Equipment QC omitted Campy jars. The root is a missing equipment-QC process, not "the night technologist is careless."

Fishbone (Ishikawa). Draw spines for people, process, equipment, materials (media and reagents), environment (temperature, CO2, anaerobic or microaerophilic atmosphere), and measurement (QC organisms, timers). Plot the facts, then pick corrective actions that change the spine that actually failed.

RCA belongs after a sentinel miss (a sterile-site pathogen not cultured or not reported) and after repeated or unexplained QC failure. Retraining is appropriate when skill was the cause; it is not a universal close-out. Document the investigation, the corrective action, and a check that the action worked (the next Campy QC and a patient-like unknown grow). Do not discard implicated media, printouts, or worksheets until the investigation has what it needs. Do not release a batch of patient results "because they look reasonable" while QC is still out.

Quality control that M tests

Media QC. Challenge sterility (uninoculated incubated medium shows no growth), growth promotion (stock strains grow as expected), and selectivity or differential performance (inhibitors suppress what they should; MacConkey shows lactose fermentation as expected). Perform user QC on new lots and new shipments per SOP. In-house prepared media get full organism challenges. Commercially prepared media still need visual inspection (color, hemolysis, thickness, expiration, contamination). Media whose failure would miss a fastidious or enteric pathogen—chocolate, Campy, modified Thayer-Martin, selective enteric media—are the ones exams expect you to organism-challenge, not merely glance at.

Stain QC. Gram stain: known gram-positive and gram-negative controls (S. aureus and E. coli are the classic pair) each day of use. Acid-fast: known positive and negative slides. If controls look wrong, stop patient smears. Over-decolorizing (everything gram-negative) and under-decolorizing (everything gram-positive) are analytic QC failures, not evidence that the patient has two cell walls.

Reagent QC. Catalase, oxidase, coagulase, PYR, indole, hippurate, and kit reagents need positive and negative controls on the schedule the SOP and manufacturer require (often each day or lot of use). Expired oxidase reagent is not "probably fine."

AST QC. Use CLSI-recommended ATCC QC strains for the method (commonly E. coli ATCC 25922, S. aureus ATCC 25923 or 29213, P. aeruginosa ATCC 27853, E. faecalis ATCC 29212). Out-of-range zones or MICs: repeat, investigate disks or panels, incubator, inoculum, and the QC strain—do not release patient AST from that run until QC is in control. A concerning patient MIC is not permission to ignore failed QC.

Equipment. Check incubators (typically 35 ± 2 °C for routine bacterial culture), CO2, anaerobic indicators, refrigerators and freezers, and blood-culture instrument status on the SOP schedule. Calibrate thermometers. Use autoclave biological indicators. Certify biosafety cabinets on schedule. MALDI and automated ID/AST systems follow manufacturer function checks and QC organisms.

Failed QC correlates one-to-one with patient-result hold for that method, lot, or instrument. Document the failure, the investigation, the corrective action, and the first in-control QC before resuming.

Point-of-care testing in microbiology

Microbiology POCT on M is rapid antigen (and some cartridge molecular) testing for influenza, group A strep, and SARS-CoV-2, sometimes RSV. Waived tests require following the manufacturer's instructions exactly, operator training, and the QC the insert and SOP require: an internal control on each device plus external positive/negative QC on new lots or kits and at defined intervals. Moderate-complexity POCT (many rapid molecular platforms) adds CLIA moderate rules: tighter QC, PT when required, and the competency methods that apply (19.3).

Waived status is not an exemption from QC, competency, or two-identifier patient identification. Nursing and ED operators who run the kits are testing personnel under the CLIA certificate; the laboratory director still owns the method. If external QC is out, stop patient testing on that kit. Do not report a faint patient line obtained while the positive control was negative. Do not substitute a different brand's swab or transport liquid in a waived kit. Do not autoverify POCT when the internal control failed.

Exam traps

1. Releasing CSF Gram stains after both QC organisms look gram-negative.
2. Closing a missed-organism event with "counseled the tech" and no media or atmosphere check.
3. Treating commercially prepared Campy or chocolate agar as no-QC wallpaper.
4. Reporting patient AST with failed ATCC QC because the floor "needed results."
5. Continuing waived influenza testing with failed external QC.

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