Spirometry and paediatric pulmonary-function testing — structured clinical encounter

Station brief (candidate)

You are the paediatric registrar in a respiratory clinic. An 11-year-old boy has a year of cough and intermittent wheeze, worse at night and on running, and normal growth. His spirometry report and flow-volume loop are in front of you. The team asks you to judge whether the test is trustworthy, interpret the pattern, decide what further lung-function testing is warranted, and explain the findings to the boy and his mother. You have 12 minutes with the family and 5 minutes for examiner discussion. [10]

Information available on request

• Two efforts are recorded as acceptable and repeatable, with a good start, no cough, a full expiration and matching values. [1]
• Baseline: FEV1/FVC ratio below the lower limit of normal (z-score about minus 2), a scooped expiratory limb, FVC within the normal range. [2]
• After an inhaled bronchodilator, FEV1 rises by more than ten percent of the predicted value. [2]
• On a previous clinic visit, spirometry when he was symptom-free was entirely normal. [10]
• No chest-wall deformity, no clubbing; atopic eczema and allergic rhinitis are present. [10]

Tasks

1. State whether you trust this test and why. [1]
2. Interpret the pattern and the bronchodilator response, using the correct reference framework. [2] [3]
3. Explain how the result contributes to a diagnosis of asthma and its key limitation. [10]
4. Decide whether further lung-function testing is needed. [2]
5. Explain the findings to the boy and his mother in plain language. [12]

Expected approach (examiner notes)

1. I trust the test because both efforts are recorded as acceptable — a good hesitation-free start with a small back-extrapolated volume, no cough in the first second, a complete expiration and no leak — and repeatable, with the two largest FVC and FEV1 values agreeing within the accepted margin. Quality must be confirmed before interpretation, because a submaximal or coughing effort produces low values that mimic disease. [1]

2. The baseline pattern is obstructive: the FEV1/FVC ratio is below the lower limit of normal with a scooped expiratory loop, and I judge that against the Global Lung Function Initiative z-score for his age, height, sex and ancestry rather than a fixed 0.70 ratio. His z-score of about minus 2 is clearly abnormal. After the bronchodilator his FEV1 rises by more than ten percent of predicted, which meets the 2022 ATS/ERS definition of a significant bronchodilator response, demonstrating variable, reversible airflow obstruction. [2] [3]

3. The reversible obstruction is an objective criterion that supports asthma within the diagnostic algorithm, and it fits his symptom pattern and atopic background. The key limitation is that lung function is often normal between episodes — his own earlier symptom-free test was normal — so a normal or non-reversible spirometry can never exclude asthma; here the test is confirmatory, but a normal test would not have been reassuring. [10]

4. No additional lung-function testing is needed to explain this result, because spirometry has already shown reversible obstruction and the FVC is normal, so restriction is not in question and lung volumes are unnecessary. I would use spirometry longitudinally to monitor control and would consider a bronchial challenge only if a future symptomatic presentation showed normal, non-reversible spirometry and the diagnosis remained uncertain. [2]

5. I would tell them, in plain language, that the breathing test shows his airways narrow more than they should but open up well with the reliever puffer, which fits asthma and is good news because it is treatable. I would explain that a normal test on a good day does not mean the asthma has gone, that we will use the test to keep track over time, and that the plan now is to treat and review rather than to do more tests today. [12]

Examiner probes

• "Why not use a FEV1/FVC of 0.70 to call obstruction?" Because children's normal ratios are higher and change with growth; a fixed cut-off misclassifies them, so the GLI lower limit of normal (the fifth percentile, z about minus 1.64) is used instead. [3]
• "His FVC is normal — does that rule out restriction?" A normal FVC makes clinically important restriction unlikely, and since the ratio is low the picture is obstructive, not restrictive; restriction would only be pursued if the FVC were reduced with a preserved ratio, and then only by measuring lung volumes. [2]
• "If the next test is normal, what will you conclude?" That his airways are open at that moment, not that he does not have asthma; a normal test never excludes it. [10]