Comments on: Analysis of cerebrospinal fluid for xanthochromia versus modern computed tomography scanners in the diagnosis of subarachnoid haemorrhage: experience at a tertiary trauma referral centre

We read with interest the study by Goyale et al. ¹ comparing the use of cerebrospinal fluid (CSF) xanthochromia analysis to modern computed tomography (CT) scanners in the diagnosis of subarachnoid haemorrhage (SAH). It was surprising that 5 out of 11 patients in their study, where initial CT head was negative but CSF xanthochromia was positive for bleed, were confirmed to have SAH. ¹ Indeed, in one of these five patients, on second review of the CT scan, evidence of SAH was noted. With regard to the other four patients, the time from onset of symptoms to presentation at emergency department (ED) was between 4 h and 14 days (mean 62 h). It is suggested in the literature that the sensitivity of CT head (and of CSF xantochromia) is poor beyond 10 days, for which reason MRI head is recommended if presentation is later than this.^2,3 In a similar UK-based study, none of 21 patients were diagnosed with SAH where initial CT head was negative, but CSF xanthochromia was positive for bleed. ⁴ That study also showed that 266 patients where initial CT head was negative also had negative CSF xanthochromia. ⁴ Together, these findings suggest that modern CT scanners do indeed have nearly 100% sensitivity in excluding SAH. Our assumption is that the findings of Goyale et al. ¹ may, in part be due to late presentation of patients (beyond 10 days of initial symptoms) to the ED. We agree with the conclusion that CSF xanthochromia remains a vital service but for screening of SAH rather than diagnosis. Moreover, many other studies have documented that CSF xanthochromia has excellent negative predictive value for SAH, but lacks sensitivity limiting its use in diagnosis. ⁵

In their study, there were six patients where initial radiology (CT/CTA/MRI) confirmed SAH but who also had a lumbar puncture performed. We found this too to be an unusual practice; in patients where initial head radiology reveals a bleed, CSF xanthochromia testing has little to offer and delays referral to neurosurgery. ⁶

Goyale et al. conclude their work by determining the economic viability of offering CSF xanthochromia analysis out-of-hours (OOH). They base their costing on saved hospital beds through early discharge of patients who have negative CSF xanthochromia. However, in another study, it was documented that a negative CSF xanthochromia result rarely results in early discharge of patients, due to various administrative barriers. ⁴ It would be interesting to determine if offering the service OOH is indeed cost-neutral or cost-saving. This would help answer an ongoing debate across the UK about the benefit of OOH CSF xanthochromia analysis.