Table 2.

Summary of the risk stratification scheme, as recommended by the WMS 2024 guidelines¹

Risk of developing altitude illness	Risk criteria
Low risk	All of the following: • History of no or mild AMS (in those with prior travel to high altitude) • Will sleep at altitude <2800 m on day 1 of the high altitude travel • Will not ascend more than 500 m per day above 3000 m • Will have one extra day for acclimatisation after every 1000 m of ascent
Moderate risk	Any of the following, without any high risk features: • History of moderate or severe AMS • Will sleep at altitude 2800-3500 m on day 1 • Will ascend more than 500 m per day above 3000 m, but has extra days for acclimatisation after every 1000 m of ascent
High risk	Any of the following: • History of HACE/HAPE • Will sleep at altitude >3500 m on day 1 • Will ascend more than 500 m per day above 3000 m, without keeping any extra day for acclimatisation after every 1000 m of ascent

AMS=acute mountain sickness; HAC=high altitude cerebral oedema; HAPE=high altitude pulmonary oedema