Acute mountain sickness (AMS) affects more than 25% of individuals ascending to 3500 m (11 500 ft) and more than 50% of those above 6000 m (19 700 ft). AMS may progress from nonspecific symptoms to life-threatening high-altitude cerebral edema in less than 1% of patients. It is not clear how to best diagnose AMS.
To systematically review studies assessing the accuracy of AMS diagnostic instruments, including the visual analog scale (VAS) score, which quantifies the overall feeling of sickness at altitude (VAS[O]; various thresholds), Acute Mountain Sickness-Cerebral score (AMS-C; ≥0.7 indicates AMS), and the clinical functional score (CFS; ≥2 indicates AMS) compared with the Lake Louise Questionnaire Score (LLQS; score of ≥5).
Searches of MEDLINE and EMBASE from inception to May 2017 identified 1245 publications of which 91 were suitable for prevalence analysis (66 944 participants) and 14 compared at least 2 instruments (1858 participants) using a score of 5 or greater on the LLQS as a reference standard. To determine the prevalence of AMS for establishing the pretest probability of AMS, a random-effects meta-regression was performed based on the reported prevalence of AMS as a function of altitude.
AMS prevalence, likelihood ratios (LRs), sensitivity, and specificity of screening instruments.
The final analysis included 91 articles (comprising 66 944 study participants). Altitude predicted AMS and accounted for 28% of heterogeneity between studies. For each 1000-m (3300-ft) increase in altitude above 2500 m (8200 ft), AMS prevalence increased 13% (95% CI, 9.5%-17%). Testing characteristics were similar for VAS(O), AMS-C, and CFS vs a score of 5 or greater on the LLQS (positive LRs: range, 3.2-8.2; P = .22 for comparisons; specificity range, 67%-92%; negative LRs: range, 0.30-0.36; P = .50 for comparisons; sensitivity range, 67%-82%). The CFS asks a single question: "overall if you had any symptoms, how did they affect your activity (ordinal scale 0-3)?" For CFS, moderate to severe reduction in daily activities had a positive LR of 3.2 (95% CI, 1.4-7.2) and specificity of 67% (95% CI, 37%-97%); no reduction to mild reduction in activities had a negative LR of 0.30 (95% CI, 0.22-0.39) and sensitivity of 82% (95% CI, 77%-87%).
The prevalence of acute mountain sickness increases with higher altitudes. The visual analog scale for the overall feeling of sickness at altitude, Acute Mountain Sickness-Cerebral, and clinical functional score perform similarly to the Lake Louise Questionnaire Score using a score of 5 or greater as a reference standard. In clinical and travel settings, the clinical functional score is the simplest instrument to use. Clinicians evaluating high-altitude travelers who report moderate to severe limitations in activities of daily living (clinical functional score ≥2) should use the Lake Louise Questionnaire Score to assess the severity of acute mountain sickness.