As per the Indian Chest Society and National College of Chest Physicians, spirometry is useful for the diagnosis of obstructive and restrictive lung diseases and can be helpful for prognostication in several conditions such as COPD, asthma, bronchiectasis, ILD, and neuromuscular diseases.

Spirometry is an underutilised pulmonary function test in India. Keeping in view the simplicity and the usefulness of spirometry, the Indian Chest Society and National College of Chest Physicians (India) jointly supported an expert group to provide recommendations for spirometry in India. The consensus statement includes recommendations for planning, performing, and interpreting spirometry in a systematic manner.

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Let us look at some of the key recommendations:

General indications of spirometry for diagnostic purposes

Recommendation: Spirometry is useful for the diagnosis of obstructive and restrictive lung diseases

• For the diagnosis of chronic obstructive pulmonary disease (COPD), demonstration of airflow obstruction in spirometry is essential as history and physical examination have sensitivity of only about 67%
• Apart from COPD, spirometry should also be used to confirm the clinical diagnosis of asthma

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General indications of spirometry for prognostication and monitoring

Recommendation: Spirometry is useful for prognostication in several conditions such as COPD, asthma, bronchiectasis, interstitial lung disease (ILD), and neuromuscular diseases.

Recommendation: Periodic spirometry should be performed to monitor disease progression in ILD. Periodic spirometry is also useful in other conditions such as COPD, asthma, and bronchiectasis.

In COPD, worsening airflow limitation is associated with increased mortality, risk of exacerbations, and hospitalisation. However, due to the presence of several COPD phenotypes, airflow limitation alone may not adequately predict disease progression.

In asthma, the usual practice is symptom assessment rather than spirometry measurements. This is on account of the wide variability observed with forced expiratory volume in 1st (FEV1) measurements. However, in some asthmatic patients such as in the elderly and those with long-standing asthma or severe disease (who may complain of fewer symptoms despite significant reduction in FEV1), assessment of FEV1 may be useful. In these groups of patients, FEV1 assessment may allow better optimisation of therapy. FEV1 is also useful to assess prognosis in asthma.

An obstructive pattern in spirometry is associated with a higher risk of Pseudomonas colonisation of the airway; while both obstructive and restrictive patterns have been linked with increased disease severity and elevated risk of hospitalisation.

In idiopathic pulmonary fibrosis (IPF), serial measurement of forced vital capacity (FVC) is one of the most useful parameters for assessing disease progression. FVC decline by 10% (over 6–12 months) is associated with decreased survival in IPF.

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General indications of preoperative spirometry for risk assessment of postoperative pulmonary complications

Recommendation: Risk assessment of patients undergoing cardiothoracic surgeries should be done by spirometry.

Recommendation: For patients undergoing non-cardiothoracic surgery, spirometry should be done for patients suspected to have COPD and other chronic lung diseases.

In patients undergoing thoracic surgeries, the severity of airway obstruction is a major predictor of morbidity and mortality. The significance of airway obstruction may be more pronounced in patients who undergo lung resection.

COPD is associated with postoperative pulmonary complications following both thoracic as well as non-thoracic surgery. However, it should be noted that a mere reduction in spirometry parameters has not been independently associated with an increased risk of postoperative pulmonary complications after non-thoracic surgery.

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General indications of spirometry for disease screening

Recommendation: Routine use of screening spirometry is not recommended for the diagnosis of COPD or occupational asthma.

Spirometry has been able to demonstrate airflow limitation in a significant proportion of the subjects in various population-based studies (which included current or former smokers). However, it is found that many subjects diagnosed with airflow limitation by screening spirometry are likely to be asymptomatic and may not need any intervention. Additionally, numerous randomised control trials have demonstrated that adding spirometry to the available interventions for smoking cessation does not increase the rate of smoking cessation. Hence, the consensus does not recommend screening asymptomatic subjects for COPD.

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Minimum numbers of maneuvers to be performed during spirometry

Recommendation: At least three acceptable spirograms should be obtained during a spirometry session.

A study which evaluated the utility of performing multiple maneuvers for spirometry, found that the FEV1 and FVC values were obtained in the following situations:

• Average of the best two spirograms of five acceptable spirograms
• Average of the best two spirograms of first three acceptable spirograms
• Single best spirogram of first three acceptable spirograms.

The study found that all the values were nearly similar and correlated with each other with a correlation coefficient >0.99. Hence, at least three acceptable spirograms during spirometry is recommended.

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Interpretation of spirometry data

Recommendations:

• A spirometric variable is to be reported as abnormal when the values obtained are less than what is generally expected in apparently healthy individuals of similar age, gender, body habitus, and ethnicity
• Statistically derived lower limits of normal (LLN) should be used in preference to fixed cut-offs for identifying abnormal values
• FEV1/VC less than the LLN should be interpreted as diagnostic of obstructive ventilatory defect
• VC below the LLN, with normal or increased FEV1/VC, may suggest a restrictive defect
• VC greater than the LLN usually rules out the presence of a true restrictive defect
• Diagnosis of true restriction cannot be made using spirometry alone and requires a measurement of the TLC
• Reduction of both VC and FEV1/VC below LLN may suggest either obstructive or mixed defect, and estimation of TLC may be necessary to differentiate between these two patterns

Spirometric data interpretation involves evaluation of numerical values for only three variables: FEV1, VC, and FEV1/VC. Only a spirometry record with normal FEV1, VC, and FEV1/VC (i.e., all values above their respective predicted LLN values) should be interpreted as being normal. Interpretation of borderline values should be done with caution and would require additional clinical information and/or other test results to make decisions.

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Categorising the severity of an abnormal spirometry report

Recommendation: Severity assessment of both restrictive and obstructive defects on spirometry should be based on FEV1 values.

Recommendation: Impairment of pulmonary function (obstructive or restrictive) can be categorized as mild, moderate, and severe when FEV1 is ≥70%, 50%–69%, and <50% predicted, respectively.

FEV1 (% predicted) is traditionally used to classify the severity of impaired lung function in obstructive airway diseases; it has also shown to predict mortality from both cardiovascular and respiratory diseases.

In asthmatics, FEV1 is helpful in predicting long-term outcome as well as risk of disease exacerbation. Spirometric indices also correlate well with respiratory symptoms and other aspects of quality of life.