An inability to achieve three acceptable and repeatable measurements provides no certainty that the best value is indeed a true reflection of the patients lung function.
Infrequently however, there are times when the standard cannot be met. This may be due to poor patient cooperation or technique, or simply down to the nature of their condition; patients with certain neuromuscular diseases for instance, or those with a severe cough from pulmonary fibrosis may find the test difficult, if not impossible to repeat.
In these circumstances you have two choices. Either you must discard all efforts and attempt these on a different day, or report the best result and highlight the sub-standard nature of it; thus advising the requester to interpret with care.
Discarding results based on poor accuracy or repeatability is not always necessary. Consider this circumstance:
Clinical reason for spirometry: “is there any evidence of airways obstruction?”
Spirometry result shows: “a 100% of predicted FEV1 and a 90% of predicted FVC with a normal shaped flow-volume loop, however, the patient does not meet the end of test criteria.
Whilst the test may not meet the required standards, the result also does not show airways obstruction. The test still has clinical value, but ensure a thorough technical report is written to highlight the problems with technique. Generating serial measurements over time in patients with poor technique may show variability, although in reality this may have little pathological significance.
Clinical judgment should be used to determine whether the data values and curves are unacceptable to the degree that they would lead to a misinterpretation of respiratory health. Ultimately however, three accurate and repeatable spirometry measurements is achievable for the vast majority of patients.
A full inspiration prior to blowing
A full expiration to RV
Effort meets start of test criterion and end of test criterion
A sharp rise to PEF is achieved
No cough or other artefact detected, particularly in the first second
A full and rapid inspiration following the FVC manoeuvre
Three superimposable curves of the volume-time and flow-volume graphs
Repeatable PEF and shape of FVL
FEV1 and FVC values are repeatable (within 100mls or 5%)
The best result quoted
The more a patient repeats the incorrect technique, the more difficult it will be to change this
It is important to note that some may take longer than others with several more attempts to get right. The ability to achieve these values in quick succession is certainly down to your coaching and demonstration skills, clear instruction and astuteness in detecting errors early and rectifying them quickly.
