Diagnosis of subarachnoid haemorrhage: Systematic evaluation of CT head diagnostic accuracy and comparison with the 2022 NICE guidelines.

Introduction: Aneurysmal subarachnoid haemorrhage has a high incidence, and morbidity. It has been suggested that a negative non-contrast CT head can rule out SAH if performed within 6 h of symptom onset. Research question: What is the sensitivity of CT head at ruling out SAH stratified by time-point, and what is the potential impact of omitting Lumbar Puncture (LP) from the diagnostic pathway? Material and methods: Systematic review and meta-analysis (PROSPEROID CRD42022379929). Three databases were searched, and articles published between January 2000-May 2022 included (Search date 27 Results: 63 articles were included (38,237 patients, 7673 with SAH). Pooled CT head sensitivity was 0.94 for excluding SAH (22 studies, 95% Confidence Interval [CI] 0.90-0.97). At <6 h, CT head sensitivity was 0.995 (6 studies, 95% CI 0.941-1.000). Most studies (57.1%, n = 36/63) were classified as high risk of bias. If LP was removed from the diagnostic pathway in the UK, assuming an incidence of 4800 SAH per-year, 336 SAH would be missed per-year, 24 per-year if LP was removed for negative CT < 6 h (95% CI 0-278) and 58 per-year if mean sensitivity is used (95% CI 0-240). Discussion and conclusion: CT head appears to be highly sensitive at excluding SAH <6 h from symptom onset. High quality, prospective data is required to further established the utility of early (<6 h) negative CT head. We recommend that if there is strong clinical suspicion of SAH, yet CT head is reported negative <6 h of symptom onset, that a LP be performed.