10 steps to checking your spirometry result


Lindsay Zurba - Education for Health Africa, e-mail: linds@educationforhealth.africa

Peter Stanyer - Stanyer Electroserve, e-mail: peter@stanyersa.com


The 10-step process, outlined in Figure 1, ensures that best practices for data ­validation, interpretation and record ­keeping are adhered to in the assessment of every spirometry test. This 10-part ­series briefly outlines each step, one-by-one.

Figure 1. The recommended 10-step process to ensure your spirometry result derives from best practices for data validation, interpretation and record keeping


In a spirometry test, the measured forced vital capacity (FVC) and forced expiratory volume (FEV1) are interpreted from a series of at least three acceptable forced expiratory curves. The data can be interpreted as either the best test or the best curve.

The (new) best test is created by the software, and uses the highest FVC and FEV1 values from the three best blows, not necessarily from the same ‘blow’ attempt. The FEV1/FVC ratio is calculated and other variables are derived, if required, for diagnostic or interpretive purposes, e.g. the peak expiratory flow (PEF) or forced expiratory flow (FEF25-75%).
Alternatively, the best curve can be selected for interpretation. This is the blow from an acceptable curve with the largest sum of FVC and FEV1 of the three best blows. This best curve is then used to derive other variables e.g. PEF or FEF25-75%.

Although all spirometry software should create a best test, using the highest FVC and FEV1 from different curves, many spirometers have defaults set to something different. Users are encouraged to review the settings to ensure that the best test method is used for interpretation.

These points are illustrated in Table 1. The best blow is Trial 4 – the blow with the highest sum of FVC and FEV1. The best test, however, is the ‘new’ test created by the software, and comprises the highest FVC of the three best blows (4.04 L from Trial 4), and the highest FEV1 from the three best blows (3.04 L from Trial 2). This creates a new FEV1/FVC ratio (75.3%). These are the values that are measured against the predicted values and are expressed as a percentage of predicted (or absolute %, in the case of the FEV1/FVC), and Z-scores for interpretation.

Table 1. Spirogram illustrating the best curve (Trial 4) and best test (Best)




Founded 22 years ago, Stanyer Electroserve is a South African-based company that provides sales, service and calibration of audiometers, spirometers and vision screeners, across the African continent. Our technicians have both the experience and the qualifications to assure you the highest quality and standards of service.

We offer a variety of occupational health-related short courses including:
Spirometry, Audiometry, Vision Screening, Wellness, HIV & Counselling, Health Risk Assessment, Family Planning, Physical Examination and Health Assessment, Occupational Health Auditing Training, Peak Flow.

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