A comparison of the individual best versus the predicted peak expiratory flow in patients with chronic asthma

In the management of patients with asthma, peak expiratory flow (PEF) monitoring is used and based on the individual best PEF or the predicted PEE Recent international guidelines have recommended the use of the best PEF rather than the predicted PEF as an index, although there is little evidence to support which index is more appropriate. Therefore, we investigated the relationship between the best PEF and the predicted PEF in 166 consecutive asthmatic patients to see which value would be the better basis for their PEF monitoring. All eligible patients had undergone treatment for their asthma for over 6 months and were asked to measure their PEF four times a day. The best PEF was defined as the maximal PEF achieved at any time from all previous measurements. The predicted PEF was calculated based on a report on the standard PEF in normal Japanese subjects. The mean best PEF was significantly higher than the mean predicted PEF (p < 0.001). There was a strong correlation between the best PEF and the predicted PEF (r = 0.77, p < 0.001). However, in 72 patients (43%) the ratio of the best PEF to the predicted PEF was over 110%, and in 20 patients (12%) the ratio was lower than 90%. The best PEF was higher than the predicted PEF in 76 patients (46%) and lower in 22 patients (13%) by more than 50 L/min. These results suggest that when the predicted PEF was used as the index, pulmonary function was either underestimated or overestimated in over half of these patients. Therefore, the best PEF may be the better index for the management of patients with asthma.