Spirometry Test Flags \"Not Repeatable\" Even Though Every Maneuver Passed

What's happening

Spirometry has two separate quality checks, and it's easy to pass one and miss the other. The first check is per-maneuver: did that single forced blast look like a real, complete effort. The second check is repeatability: do the subject's best efforts agree closely enough with each other. It's entirely possible for every individual maneuver to grade "acceptable" and for the test as a whole to still fail, because repeatability compares maneuvers against each other, not against a single quality standard.

The repeatability criterion on the CCS-200 is simple: the difference between the subject's largest and next-largest FVC must be 0.150 L or less, and the same 0.150 L window applies separately to FEV1. If either value swings more than that between the two best efforts, the test flags as not repeatable, even though each maneuver on its own looked fine.

The most common cause by far is incomplete inspiration before the blast. If the subject doesn't take a full, deep breath in before forcing the air out, the starting lung volume is different from one maneuver to the next, and that shows up directly as a bigger swing in FVC and FEV1. The blast itself can be forceful and well-executed and still produce inconsistent results if the breath in front of it wasn't consistent.

Try these in order

1. Coach the subject on the inhale, not just the exhale. Before each attempt, walk them through taking a full, deep breath in — all the way to total lung capacity — and pausing briefly before the forced blast starts. Most repeatability failures trace back to this step being rushed.
2. Watch the inhale on each attempt, not just the flow trace afterward. A subject who's tired, talking, or rushed between efforts will often shorten the breath in without anyone noticing until the numbers come back inconsistent.
3. Compare the largest and next-largest FVC and FEV1 after each new attempt. You're looking for both values to land within 0.150 L of each other. If FVC is close but FEV1 isn't (or the reverse), that's still a fail — both have to hold.
4. Have the subject repeat maneuvers. The CCS-200 allows up to 8 maneuvers in a single session to reach repeatability, so there's room to try again with better coaching before treating the session as a problem.
5. Build in a short rest between efforts if the subject seems fatigued. A full forced exhalation is tiring, and effort quality — including the depth of the following inhale — tends to drop off if attempts are stacked back to back with no break.

If it still won't pass

If you've coached the inhale, given the subject a brief rest, and worked through several attempts within the 8-maneuver limit and it's still not repeatable, that's more often a subject-effort or subject-condition issue (fatigue, chest discomfort, or difficulty following the instruction) than an instrument problem. Note that on the test record rather than continuing to run maneuvers indefinitely — a test that never repeats after a full, well-coached set of attempts is itself useful clinical information.

If the spirometer's daily calibration is current and multiple different subjects are showing this same pattern in the same session, treat that as a possible equipment issue rather than a coaching issue across the board — see our daily calibration and syringe check guide to confirm the unit itself is reading consistently before you assume every subject is the cause.

When to call us

• Repeatability is failing across several subjects in the same session, not just one.
• The daily calibration check is passing but the printed flow-volume traces look visibly abnormal (not just inconsistent in volume).
• You want a second look at a specific subject's traces before deciding how to document a test that never reached repeatability.

You can reach us at (513) 891-0868 or service@fosterinstruments.com.