2017 ERS Methacholine Challenge Standards

After a couple years of waiting for the new methacholine standards to be released “any day now”, they were finally published in this month’s issue of the European Respiratory Journal. The standard is an open access article and can be downloaded by anyone.

The length of time taken to develop the standard was acknowledged and although active ATS participation was withdrawn because the original timeline was not met, for the most part the original ATS participants continued with the task group and the standard has been officially endorsed by the ATS.

The biggest difference between the 1999 standards and those from 2017 is the change from PC20 (provocative concentration causing a 20% decline in FEV) to PD20 (the provocative dose causing a 20% decline in FEV1) as the primary endpoint and this alone will make a difference in how methacholine challenges are performed and calculated.

The 1999 standard included both tidal volume and dosimeter protocols. The dosimeter protocol consisted of 5 breaths to TLC. The 2017 standards state that a dosimeter may be used but that this is primarily to make counting breaths and calculating the cumulative dose easier and that inhalations to TLC are specifically contraindicated due to “the bronchodilating or bronchoprotective effect of a maximal inspiratory manoeuvre with a breathhold at TLC”.

Other differences include:

  • The 1999 standard had both absolute and relative contraindications. There are only contraindications in the 2017 standard.
  • Absolute contraindications in the 1999 standards included an FEV1 < 50% of predicted (or < 1.0 L, age group unspecified) and for the 2017 standard it is an FEV1 < 60% of predicted (or 1.5 L, adults) which were relative contraindications in 1999.

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