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) monit oring is used and based on the individual best PEF or the predicted PEF. Re cent international guidelines have recommended the use of the best PEF rath er than the predicted PEF as an index, although there is little evidence to support which index is more appropriate. Therefore, we investigated the re lationship between the best PEF and the predicted PEF in 166 consecutive as thmatic 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. Th e best PEF was defined as the maximal PEF achieved at any time from all pre vious measurements. The predicted PEF was calculated based on a report on t he standard PEF in normal Japanese subjects. The mean best PEF was signific antly higher than the mean predicted PEF (p < 0.001). There was a strong co rrelation 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 P EF was over 110%, and in 20 patients (12%) the ratio was lower than 90%. Th e 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 whe n the predicted PEF was used as the index, pulmonary function was either un derestimated or overestimated in over half of these patients. Therefore, th e best PEF may be the better index for the management of patients with asth ma.