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Spirometry Results

An FEV1 less than 80% of predicted values for the patients age, sex and height indicates obstruction, restriction or combined

An FVC less than 80% of predicted values indicates restriction or combined

An FVC within normal limits indicates normal or obstruction

An FEV1/ FVC ratio less than 70% of predicted values indicates obstruction or combined

An FEV1/FVC ratio within normal limits or higher than predicted values indicates normal or restriction


According to NICE Guidelines 2010

  • Mild Obstruction                    FEV1    >80% of predicted, ratio < 70%
  • Moderate                               FEV1    50 - 79% of predicted, ratio < 70%
  • Severe                                   FEV1    30 - 49% of predicted, ratio < 70%
  • Very Severe                          FEV1    <30% predicted, ratio <70%


Differential Diagnosis

Obstruction can be due to Asthma: COPD: deficiency of alpha1antitrypsin: foreign body: lung cancer

Restriction can be due to fibrosing alveolitis: kyphoscoliosis: pneumoconiosis: kyphoscoliosis: asbestosis or obesity


Reversibility Test Result


When FEV1 increases by 400mls or more this will support a diagnosis of asthma. A response of less than this will support a diagnosis of COPD