RPFT common mistakes
RPFT · Understand the traps and how to avoid them.
Entering the patient's self-reported height (or a height estimated from arm span without documenting it) into the spirometer before testing, then reporting percent predicted from those values.
It saves time in a busy schedule, patients often know their height, and the entry field will accept any number without questioning it. Candidates underestimate how much a 2–3 cm error shifts predicted FVC and TLC.
What to do instead
Measure standing height with a stadiometer at every visit, shoes off, head in the Frankfurt plane; record the measured value and the reference equation set used. If height cannot be measured, document the surrogate (e.g., recumbent length, ulnar length) and the equation that uses it, and flag the predicted values as estimated.
Asking 'did you use your inhalers today?' and accepting 'no' without identifying the specific agents, doses, and times, then proceeding with testing.
Candidates memorize that bronchodilators must be withheld but not the class-specific intervals, and the question feels like a formality once the patient says no.
What to do instead
Work from a written withholding checklist listing drug classes with their required intervals (short-acting beta-agonists, long-acting beta-agonists, short- and long-acting antimuscarinics, leukotriene modifiers, antihistamines for challenge testing). Record the agent, last dose, and date/time on the requisition, and reschedule when the interval has not been met rather than testing and qualifying the result.
Performing the daily 3-L syringe calibration check once, seeing it fail, and immediately repeating injections until a passing value appears, then charting only the passing result.
The check is treated as a box to tick before the first patient, and repeating the maneuver is faster than investigating. Candidates often do not realize that erasing the failed attempts removes the evidence needed to decide whether the device or the technique was at fault.
What to do instead
Perform the syringe check at the start of each testing day and after any flow-sensor change, leak repair, or software update. Record every injection, the mean measured volume, the calculated percent error, and the ambient conditions. If error exceeds the tolerance in the lab SOP (commonly ±3.5% for volume per ATS 2019), troubleshoot in a fixed order (syringe seals, adapter leaks, sensor contamination, temperature correction), document the corrective action, and repeat the full check before testing any patient.
Starting DLCO testing after only a single-point or skipped gas calibration, without a system leak test or a documented biological control.
DLCO equipment sits idle more than spirometry, so daily calibration is easy to skip when the first patient arrives. The analyzer display looks plausible, and a drifted CO cell produces values that seem physiologically reasonable.
What to do instead
Run the manufacturer's daily two-point calibration with reference gases for the CO and tracer analyzers, verify the calculated CO uptake and anatomic dead space, perform the system leak test before the first subject, and run the lab's biological control subject on the schedule defined in the SOP. Chart the control value with its acceptable range; do not test patients if the control falls outside the range until the cause is corrected.
Stopping the spirometry session after one acceptable maneuver, or after several efforts that are acceptable but differ by more than 150 mL, and reporting the best FEV1 and FVC from that set.
Patients tire quickly and cough, and the technologist wants to avoid another paroxysm. Candidates also confuse 'acceptable' (free of artifact) with 'repeatable' (consistent across efforts) and assume more maneuvers will not change the numbers.
What to do instead
Continue until at least three acceptable maneuvers are obtained and the two largest FEV1 and FVC values agree within 150 mL; if the patient cannot meet repeatability, document the reason and report the result with an explicit statement that repeatability criteria were not met. Review every curve for back-extrapolated volume (>5% of FVC or 150 mL, whichever is greater), end-of-test plateau, and cough or glottic closure before accepting it.
Accepting body plethysmograph loops without checking for leaks, thermal drift, or proper panting technique, and reporting TLC and airway resistance from those loops.
The software averages the loops automatically and produces a TLC number, so the tracing itself goes unexamined. Candidates also do not coach patients to keep hands off the cheeks or to pant at the correct frequency, allowing mouth pressure to lag box pressure.
What to do instead
Coach the patient to support the cheeks with the palms only, sit upright without leaning on the door, and pant at a shallow, regular rate around 1 Hz. Obtain at least three technically acceptable loops with closed shutter, verify the slope of the box pressure versus mouth pressure plot and a stable isothermal baseline, and reject loops containing leaks, swallowing, or glottic closure. Repeat after a leak repair and re-check the box pressure transducer calibration.
Labeling a study as obstructive because FEV1/FVC falls below 0.70, and grading severity from FEV1 percent predicted without reference to the lower limit of normal or z-scores.
The 0.70 ratio is widely taught and easy to apply, and percent predicted is what most software displays most prominently. Candidates do not consistently apply the age-related decline in the ratio, so older patients are overcalled.
What to do instead
Compare FEV1/FVC with the lower limit of normal (z = -1.645) from the reference equation set matching the patient's age, sex, and ethnicity, and interpret the pattern using the ATS/ERS interpretive algorithm: obstruction when the ratio is below the LLN, severity from FEV1 z-score, and a restrictive pattern suggested by reduced FVC with preserved ratio, confirmed by TLC. State the reference equations in the report.
Calling a bronchodilator response positive on the basis of a percent change alone (for example, a 10–12% rise in FEV1) without checking the absolute volume change, and reporting a response that does not meet criteria.
Software often flags 'percent change' as the response metric, and in a patient with a small baseline FVC a modest percentage translates to a trivial volume change - or the reverse.
What to do instead
Apply both components of the criterion: a change of at least 12% and at least 200 mL in FEV1 or FVC relative to baseline. Report the absolute and percent change for both pre- and post-bronchodilator values, verify that the post-bronchodilator maneuver meets the same acceptability and repeatability standards as baseline, and state explicitly whether the response meets criteria.
Reusing a single in-line bacterial filter across multiple patients in a session, or wiping the mouthpiece with alcohol and calling it cleaned, and moving between patients without hand hygiene.
Filters are perceived as expensive consumables and a session of six patients on one filter can look like thrift. Candidates also treat the mouthpiece as the only contaminated surface and overlook the valve, the flow sensor, and their own gloves.
What to do instead
Use a new single-use filter or mouthpiece for every patient and discard it in the exam room. Perform hand hygiene before and after every patient contact and glove change, and follow the manufacturer's validated disinfection schedule for reusable valves, sensors, and the pneumotach. Keep a cleaning log with the agent, contact time, and equipment identifiers.
Running induced-sputum collection or a coughing provocation in the same open testing area and with the same respiratory protection used for routine spirometry, without screening the patient for transmissible infection.
The lab is arranged around one testing station, and aerosol-generating procedures are treated as just another breathing test. Candidates do not recognize that induced sputum and vigorous coughing generate more infectious aerosol than a quiet forced expiratory maneuver.
What to do instead
Screen every patient for fever, cough, rash, and recent known exposure before testing and defer elective testing when active infection is suspected. Perform aerosol-generating procedures in a negative-pressure room or with local exhaust ventilation, use airborne precautions with a fit-tested N95 or equivalent for the technologist, allow the room's air-change time before the next patient, and follow the facility's transmission-based precautions policy for disinfection afterward.