4.2 QC vs QA, Internal vs External QC, and Proficiency Testing

CMLA I.2.A.2 tests whether you can know and perform quality control and quality assessment (QC/QA) within the laboratory assistant's scope. That includes the difference between QC and QA, internal versus external QC, proficiency-testing (PT) rules, actually running the controls a CMLA runs, and using daily QC results. Off-label use of waived tests and confirmatory methods such as gas chromatography–mass spectrometry (GC/MS) are Chapter 5; this section stays on the QC/QA program a laboratory assistant operates.

Quick Answer: QC is the analytic check (control materials, ranges, Levey-Jennings). QA is the whole-program look at preanalytic, analytic, and postanalytic quality. Internal QC is run in your laboratory with patients. External QC is PT and peer programs. Treat PT like a patient, never share answers, never send the sample out, and never report patients when daily QC fails.

Quality Control versus Quality Assessment

Quality Control (QC) is the set of operational techniques that monitor the analytic process. You run control materials (or manufacturer-required electronic or internal checks), compare results with an acceptable range, plot or log them, and decide whether the test system may be used for patients today.

Quality Assessment (QA)—Clinical Laboratory Improvement Amendments (CLIA) language for the broader program, sometimes called quality assurance in textbooks—is the laboratory-wide system that watches the total testing process:

• Preanalytic: patient identification, collection, labeling, transport, storage.
• Analytic: calibration, QC, following the instructions for use (IFU).
• Postanalytic: result review, critical-value notification, corrected reports.

QC is a tool inside QA. Passing QC does not prove the specimen was drawn from the right patient. A QA failure (wrong labels, missed refrigerator logs, unreported critical values) can exist even when every control was in range. CLIA quality-assessment provisions for laboratory systems and postanalytic review (including 42 CFR 493.1239 and § 493.1299) sit at the program level; the assistant's job is to complete the assigned checks and escalate problems, not to write the quality plan.

Internal versus external QC

Internal QC is performed inside your laboratory, usually with the same instrument, reagents, and operators used for patients. Liquid control solutions, lyophilized controls reconstituted per IFU, and many built-in electronic checks are internal QC. What it accomplishes: it detects immediate problems—bad strip vial, deteriorated control, dirty optic, wrong code chip, operator error—before (or with) the day's patient testing.

External QC is comparison outside your own result set. The main CMLA example is proficiency testing: an approved PT provider ships unknown samples; your laboratory tests them and returns results; the provider grades you against the peer group or a reference value. Peer-group QC programs (many laboratories submit routine QC means to a vendor) are also external. What external QC accomplishes: it detects problems internal QC can miss, such as a calibration that is consistently wrong in the same direction (precise but inaccurate) because your in-house range drifted with you.

Do not call the "C" line on a rapid cassette "external QC." That line is an internal procedural control. Do not call a glucose meter's electronic simulator proficiency testing.

Proficiency testing within assistant scope

CLIA 42 CFR 493 Subpart H, especially § 493.801, sets the federal PT rules for laboratories that perform nonwaived (moderate- or high-complexity) testing.

For the CMLA:

1. Test PT like a patient. Same method, same number of times you would test a patient, same personnel who routinely do the test, same interval—not a special "PT expert" bench and not a delayed research batch (§ 493.801(b)).
2. Do not refer the sample. You must not send a PT specimen to another laboratory for analysis. Referral can cost the laboratory its CLIA certificate.
3. Do not share answers. No interlaboratory calls, texts, or "what did you get?" until after the event's reporting deadline.
4. Document. Treat the PT accession like a patient: identification, timing, reagent lots, QC status that day, and who tested it.
5. Follow the SOP. Assistants do not design the PT program, pick the PT provider, or grade the event. You perform the testing you are trained and assigned to perform.

Waived versus nonwaived CLIA expectations. Federal CLIA does not require PT enrollment for waived tests. A Certificate of Waiver laboratory must still follow the manufacturer's instructions (see 42 CFR 493.15 and waived-inspection provisions such as § 493.1775). Many manufacturers, states, and accrediting organizations still expect or recommend PT or an alternative assessment even for waived methods. If your SOP says to run the waived glucose PT or alternative assessment, you run it. Nonwaived analytes that CLIA regulates generally require PT enrollment and a passing score; that program is a laboratory director and supervisor duty, but the assistant who performs the method is the person who must not compromise the sample.

If a PT sample looks hemolyzed, mislabeled, or the wrong specimen type, stop and notify the supervisor. Do not "make it work," do not send it to the reference laboratory "just this once," and do not ask the clinic next door for their answer.

Perform the QC/QA procedures a CMLA actually does

Typical assistant-level procedures:

• Glucose meter: two levels of control solution (low and high) on each day of patient testing, when a new vial of strips is opened, after the meter is dropped, and whenever results are questioned—plus any extra frequency the IFU or SOP lists. Record lot numbers of strips and controls, expiration dates, operator identification, and pass/fail.
• Waived kit tests (for example Strep A, influenza, human chorionic gonadotropin, waived UA cassette): run the manufacturer's external positive and negative controls at the required interval (new kit lot, new shipment, periodic schedule). Confirm internal procedural controls (C line) on every patient cassette. A missing C line is invalid, not "negative."
• Waived chemistry or UA tabletop analyzer: run the assigned control levels, perform the startup function check, and complete the daily QC log before patients.
• International Normalized Ratio (INR) meter: lot-specific code chip or calibration strip as the IFU directs, then liquid QC at the required levels.

QA tasks at assistant scope are often clerical but scored: complete temperature logs, check expiration versus open-vial dating, initial the QC sheet, and escalate failures. You do not write the quality plan.

Daily QC and use of results

Daily QC is a gate, not a decoration.

• Both required levels in range → patient testing may proceed on that device.
• Any required level out of range → do not report patient results from that system. Repeat only if the SOP says a single rerun is allowed (for example, after remixing a control or repeating a known operator error). If still out, troubleshoot within training (new control bottle, new strip vial, cleaning the window), document, and notify the supervisor. Take the device out of service until it is released.
• QC in range does not authorize an expired kit, an off-label specimen type, or a refrigerator that spent the night at 15 °C. Those are QA failures.

Scenario

You are the first person at the waived-testing bench. The glucose-meter high control is 20 mg/dL above the printed range; the low control is acceptable. You do not test the waiting clinic patients "because the low was fine." You document the failure, follow the SOP repeat and troubleshooting steps, pull the meter from service if it does not recover, notify the supervisor, and wait for an in-control system. That is QC. Later the same week you notice three different operators skipped the refrigerator log: that is a QA problem you also escalate.

Exam traps

• Treating QA and QC as synonyms.
• Calling PT "internal QC" because you ran it in your building.
• Sharing PT values "to help the other site."
• Reporting patients after a failed high control because the low passed.
• Assuming waived tests have no QC because CLIA does not require PT for waived methods.

When the stem asks what QC versus QA accomplishes, name the analytic check versus the total testing process, then name the assistant action: run the assigned controls, treat PT like a patient, and stop patients when the gate fails.