Spirometer Calibration: Syringe Checks & ATS/ERS Accuracy

What is a spirometer calibration syringe check?

A calibration syringe check verifies a spirometer measures volume accurately by pushing a precisely known volume of air — typically a 3-liter calibration syringe — through the device and comparing the instrument's reading against that known value. It's the pulmonary-function equivalent of an audiometer's biological check: fast, done with a single dedicated piece of reference equipment, and able to catch a drifting or leaking system before it produces bad data on a real employee. A spirometer that under- or over-reads volume by even a small margin can push a legitimate FEV1/FVC result across a referral threshold in either direction, so the syringe check isn't a formality — it's what makes the day's test results trustworthy.

How often should spirometer calibration be verified?

Accepted pulmonary function testing practice calls for a calibration syringe check at the start of each day of testing, and again if the spirometer is moved, if ambient temperature or barometric pressure shifts meaningfully during the testing day, or if a technician gets a result that looks physiologically implausible and wants to rule out instrument error before retesting the employee. Volume displacement (bellows or rolling-seal) and flow-sensing (pneumotach) spirometers both need this check — the technology changes how the instrument measures air, not whether it can drift out of calibration.

What accuracy tolerance do ATS/ERS standards require?

The American Thoracic Society and European Respiratory Society joint spirometry standards set the accuracy target that calibration checks are measured against: a properly calibrated spirometer should read a known 3-liter syringe volume within a small percentage of the true value, corrected for ambient temperature, pressure, and humidity (BTPS correction), since gas volume changes with those conditions between the syringe and the patient's exhaled breath. A spirometer that's outside tolerance on the syringe check needs recalibration before it's used for any test that day — documented results from an out-of-tolerance instrument aren't usable for OSHA medical surveillance or fitness-for-duty determinations.

Check	Reference used	Frequency
Volume calibration	3-liter calibration syringe	Daily, before testing begins
Leak check	Sealed system, sustained pressure	Daily or per manufacturer instructions
Linearity check	Multiple syringe strokes at different flow rates	Periodic, per QA program

What causes a spirometer to fail a calibration check?

The most common causes are a leak somewhere in the tubing or mouthpiece connection, a dirty or worn flow sensor on pneumotach-style devices, a bellows or rolling-seal mechanism with mechanical drag or damage, or simply not accounting for temperature and pressure changes between calibration and testing. A syringe itself can also be the problem if its own certification has lapsed or its seal has degraded — a calibration syringe is a precision instrument and needs its own periodic verification, not just an assumption that it's still accurate.

How does a Foster technician run a spirometer calibration check in the field?

Before the first employee is tested at a scheduled visit, the technician connects the calibration syringe, enters current ambient temperature and barometric pressure into the spirometer, and performs several full strokes of the syringe at different speeds — not just one slow push — because a spirometer can read a slow stroke accurately and still miss on a fast one if the flow sensor is degraded. The tech records each stroke's measured volume against the syringe's certified 3-liter output, confirms the readings fall within tolerance, and only then starts testing employees. If a site is unusually cold, hot, or at meaningfully different elevation than the last visit, the tech re-verifies temperature and pressure inputs rather than assuming yesterday's settings still apply, since BTPS correction is only as good as the values fed into it.

What does an out-of-tolerance reading usually turn out to be?

In the field, a failed syringe check is more often a loose mouthpiece adapter or a hairline crack in the tubing than a genuinely broken sensor — both create a small leak that reads as under-volume. The next most common cause is a pneumotach sensor that's picked up moisture or debris from repeated use without cleaning between sessions, which skews flow readings without an obvious visual sign. Genuine mechanical failure of a bellows or rolling-seal mechanism is less common but shows up as a consistent, repeatable volume error across every stroke speed rather than an inconsistent one — that pattern is usually what tells a tech the unit needs to go back to the shop instead of getting fixed on-site.

Frequently Asked Questions

Can a spirometer be used the same day a calibration check fails?

No. An instrument that fails its calibration check should be corrected — leak fixed, sensor cleaned, or unit serviced — and reverified before any employee is tested on it that day.

Does BTPS correction happen automatically?

Most modern spirometers apply BTPS correction automatically using measured or entered temperature, pressure, and humidity values, but the technician still needs to confirm those input values are current and accurate for the calibration to mean anything.

Is a syringe check the same as full spirometer calibration service?

No — the daily syringe check is a quick verification a technician runs before testing; full calibration service, when needed, involves a qualified technician adjusting or repairing the instrument itself.

Foster Special Instruments provides spirometer calibration service and on-site pulmonary function testing. See more on occupational spirometry best practices.