The FEV1/FVC ratio

Traditionally, a ratio under 0.7 suggests obstructive pathology. However, you must take care as this ratio declines normally as we age, which may increase the frequency you diagnose airways disease in the elderly. Conversely, a ratio around 0.7 in young subjects may in fact indicate significant airflow abnormality.

Using standardised residuals (SR’s) to determine normality for all spirometric indices is recommended for this reason as it takes normal variation into consideration.

Normal values for the FVC and FEV1 are based on population studies and vary according to race, height, age, and gender.

Whilst the percentage predicted values are commonly referred to in published guidelines and are easy to use and calculate, it has significant limitations. In fact, the percentage predicted values of normality has no statistical or physiological validity and should only be used as a quick guide.

Normal values for the FVC and FEV1 are based on population studies and vary according to race, height, age, and gender.

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