Failed Daily Syringe Verification Before a Full Clinic Day

Arithmetic

• Mean = (2.87 + 2.86 + 2.88) / 3 = 8.61 / 3 = 2.87 L
• Percent error = (2.87 − 3.00) / 3.00 × 100 = −4.3%

Acceptance limit

• Current ATS/ERS spirometry standards require volume accuracy within ±3.5%, i.e., an acceptable 3.00 L verification falls between 2.895 L and 3.105 L. Older ATS documents used ±3% (2.91-3.09 L). The measured mean fails either criterion, so the conclusion does not hinge on which edition the laboratory cites.

Decision

• The device is out of tolerance and may not be used for diagnostic patient testing until it is corrected and re-verified. A device that under-reads by 4.3% will systematically under-report FVC (and, by extension, FEV1 in volume-displacement systems), which propagates straight into interpretation and into any longitudinal comparison.
• Next steps, in order: confirm the syringe connections are seated and the injection is slow and steady (a 3 L injection over roughly 6 seconds, not a rapid push); re-verify after allowing the syringe to equilibrate to room temperature; then perform the manufacturer's calibration/linearity procedure at multiple flows, not just a single 3 L push. Re-verify after calibration. If it still reads outside 2.895-3.105 L, remove it from service, tag it, notify the supervisor, and log the failure.
• Do not apply a mental correction factor to patient results and do not chart "calibration acceptable."

The fact that the device read consistently (2.86-2.88) rather than erratically argues against random noise and toward a systematic problem - a leak, a contaminated or moisture-fouled flow sensor, or a genuine calibration drift.

Cause 1 - leak in the circuit. A leak at the syringe-spirometer connection, a cracked syringe seal, or a mouthpiece/filter adapter not fully seated lets gas escape during injection, so the sensor registers less than was delivered.

• How to test: reconnect with firm, straight seating; re-inject slowly; substitute a known-good mouthpiece/adapter; if the spirometer has a leak test (often a small positive pressure held for a set interval), run it.
• Signature: readings that worsen when the connection is disturbed, or that improve immediately after re-seating with no calibration change.

Cause 2 - sensor drift or contamination. Moisture, mucus, or dust on a flow sensor changes its calibration; a hot-wire or pneumotachographic sensor is especially vulnerable, and a sensor that has not been cleaned or replaced on schedule will drift.

• How to test: inspect and clean or replace the sensor per the manufacturer, then repeat the manufacturer's linearity verification across several flows. A sensor that is inaccurate at low flow but accurate at high flow (or vice versa) points to contamination rather than a global offset.
• Signature: recalibration succeeds but the error returns within days.

Does cold storage explain it? Very unlikely, and the direction is wrong. If the gas inside the syringe were genuinely colder than the spirometer, it would warm and expand after entering the device, and the recorded volume would read high, not low. In practice the syringe is filled with room air at 23 °C, so the storage temperature of the hardware is largely irrelevant once it equilibrates. Temperature is worth documenting (and the syringe should be allowed to reach room temperature before use), but it is not a credible explanation for a −4.3% reading. Chasing it would waste the clinic morning.

Documentation - Friday's entry is a model of what not to do. The record must show:

• Date and time of verification, the individual values (not just "OK"), the mean and percent error, the acceptance range applied, ambient temperature and barometer, device identifier and sensor ID, and the technologist's signature/initials.
• For today: the failed verification, the corrective actions attempted, the outcome, the time the device was removed from service, and who was notified.
• Any patient results already obtained on a device later found to be out of tolerance must be flagged for review - a single unrecorded "OK" means you cannot prove Friday's clinic was valid.

Schedule management

• Because the backup is not available before noon, contact the supervisor and the ordering providers first, then reschedule or redirect. Do not silently cancel.
• Pre-operative patient: can be moved to the afternoon if the backup arrives, or referred to a nearby laboratory. Tell the surgeon's office the reason and the expected time, since the operating room schedule depends on it.
• 6-year-old with cystic fibrosis: this is the patient you protect most. Pediatric PFTs are compared against that child's own prior values over years, so a 4% systematic bias can look like disease progression or improvement. In addition, a pediatric verification should include low-flow and small-volume checks, and the filter/mouthpiece dead space must be appropriate for a child - a large pediatric filter adds dead space that the child rebreathes and can distort the measurement. Do not test a child on a device you would not use for an adult.
• General principle: a failed pre-clinic verification is a stop-work condition for diagnostic testing, not a note in the margin. The correct outcome is a short delay with clear communication, not five results of unknown validity.