6.2 Biological Controls & Proficiency Testing

Biological QC After the Hardware Passes

Mechanical devices prove the instrument can measure a known volume or pressure. Biological quality control asks a second question: Does the complete measurement chain—mouthpiece, filters, gas analyzers, software corrections, and operator technique—still produce stable results on a real person? For RPFT-level practice, biological controls are especially valuable for spirometry and DLCO, where small analyzer, timing, or BTPS/STPD pathway problems may not appear on a dry syringe alone.

Biological QC is not a substitute for the 3-L syringe, ILA, manometer checks, or blood gas multi-level controls. It is a complementary stream. Domain I.C expects candidates to know when each stream applies; Domain III.A.16 expects correct use of QC procedure data when evaluating whether results (including controls) are suitable for use.

Healthy Biological Control Subjects

Labs typically recruit healthy, cooperative adults (often staff) who can perform reproducible maneuvers and who are free of acute respiratory illness when serving as controls.

What is trended (examples):

• Spirometry: FVC, FEV1 (sometimes PEF or FEV1/FVC)
• DLCO: DLCO (and often VA or inspired volume parameters per lab policy)
• Sometimes lung volumes on box systems after mechanical verification

Bio-controls are not patients being diagnosed. Their charts answer “is the lab system stable?” not “does this person have restriction?”

Establishing Mean and SD

Before control rules mean anything, the lab must establish each bio-control’s personal baseline:

1. Collect a series of acceptable measurements over days/sessions while instruments are known good (after mechanical QC).
2. Calculate the mean and standard deviation (SD) for each key parameter.
3. Define control limits (commonly mean ±2 SD and mean ±3 SD style bands, or manufacturer/lab-defined equivalents).
4. Plot subsequent results on a Levey-Jennings-style chart (value vs time).
5. Re-establish baseline after major instrument service, software change, or if the control subject’s physiology permanently changes.

Exam caution: a single point slightly outside ±2 SD is not automatically “the patient has new disease”—for a bio-control it is a QC signal. Investigate technique, filters, calibration, gas lots, and recent service before assuming the person changed.

Control Rules (Westgard-Style Concepts at Technologist Level)

You do not need to recite every classical Westgard multirule letter-perfect for the RPFT, but you do need technologist-level judgment that mirrors those ideas:

Technologist rules of engagement:

• Do not silently delete an inconvenient bio-control result.
• Repeat once with coached technique if effort was clearly poor; if still out, treat as QC failure.
• Correlate with mechanical QC: if syringe still passes but DLCO bio-control shifted after a new CO tank, suspect gas concentration, demand valve, or analyzer span—not “FEV1 disease.”
• Document investigations and resolutions the same day.

External Proficiency Testing

Proficiency testing (PT) is an external quality assessment. An outside provider sends unknown samples (blood gas/co-ox materials are classic; some programs support PFT-related challenges where available). The laboratory analyzes them like patient unknowns (to the extent the program requires), reports results, and receives scored comparison to assigned values or peer group statistics.

For blood gas, multi-level aqueous or protein-based controls are routine QC; PT samples are separate challenges. For PFT, mechanical + biological QC are the daily backbone; external PT or inter-laboratory comparisons, where enrolled, add an outside check. Never “special-case” PT samples with extra calibration tricks that you would not use for patients—that defeats the purpose and violates PT integrity rules.

Routine QC vs Proficiency (DCO I.C.2) and QC Data (III.A.16)

I.C.2 emphasizes distinguishing routine QC procedures from proficiency testing. Exam stems may ask which activity is which:

• Daily 3-L syringe → routine mechanical QC
• Weekly staff DLCO bio-control chart → routine biological QC
• External unknown blood gas shipment scored by a PT provider → proficiency testing

III.A.16 (QC procedures data) sits in Data Management: you must know what the QC numbers mean when deciding whether patient data can be released. That includes recognizing failed controls, incomplete QC, or out-of-date verification as reasons to hold reports, not merely as paperwork afterthoughts.

Putting Streams Together — A Worked Scenario

Morning mechanical QC: 3-L syringe passes on spirometer A. DLCO analyzer zero/span passes. Bio-control “Alex” usually has DLCO mean 28 with SD 1.0. Today Alex’s acceptable maneuvers yield DLCO 23 (more than 3 SD low). Actions:

1. Confirm Alex is not ill and effort/IVC criteria were met.
2. Recheck mechanical/gas QC and tank assay/lot.
3. Inspect sample path (Nafion, desiccant, leaks).
4. If confirmed system problem → out of service for DLCO until fixed and re-verified (mechanical + bio-control or SOP equivalent).
5. If system re-checks perfectly and Alex is febrile with new anemia → document bio-control subject change; do not force the instrument offline without evidence—but re-baseline when appropriate.

The RPFT skill is structured investigation, not guessing. Biological QC amplifies real-world problems; proficiency testing proves you can get the right answer when an external scorer is watching. Together with mechanical devices, they form the Domain I.C quality net that protects every Domain II procedure result.

Link Forward

Section 6.3 places these QC streams inside laboratory quality management: SOPs, inventory, customer satisfaction, documentation, report-release authority, and serial patient testing as a quality signal.