[1] The most frequent symptoms of CMS are headache, dizziness, tinnitus, breathlessness, palpitations, sleep disturbance, fatigue, loss of appetite, confusion, cyanosis, and dilation of veins.
[4][5] CMS is characterised by polycythaemia (with subsequent increased haematocrit) and hypoxaemia; raised blood pressure in the lungs (pulmonary hypertension) can develop over time and in some cases progress to heart failure (cor pulmonale).
[6] Consensus for clinical diagnosis of CMS use laboratory values: haemoglobin in Males ≥ 21 g/dL; Females ≥ 19 g/dL, haematocrit > 65%, and arterial oxygen saturation (SaO2) < 85% in both sexes.
[1] Migration to low altitude is curative, though not immediate, as the body adapts to the normal oxygen level near sea-level and the haematocrit normalises.
Alternatively, bloodletting (phlebotomy) can be performed to lower the haematocrit temporarily; when combined with volume replacement with fluids this can have a longer effect.