AbstractIntroduction: Sub-arachnoid haemorrhage (SAH) occurs when a cerebral artery ruptures and blood leaks out into the sub-arachnoid space. This is often a catastrophic event for the individual and morbidity and mortality rates are significantly influenced by early intervention. This makes the role of the clinical biochemistry laboratory in early diagnosis vitally important, as delays in diagnosis can have a major clinical impact.
The cerebrospinal fluid (CSF) of healthy individuals is optically clear. It has, however, been recognised for over a century that it can become coloured (xanthochromia) following a cerebrovascular incident such as a SAH. This has made the main role of the clinical biochemistry laboratory in SAH diagnosis that of detecting xanthochromia in the CSF.
The majority of laboratories which offer a xanthochromia screening service use the national guidelines that are based upon ultra-violet scanning spectrophotometry (350 nm to 600 nm). This analytical technique is not without its problems: it is subjective, has a possibility of inter-operator variability and due to the specialised nature of the test can take many hours or even days for a result to be issued.
This project aimed to improve the current laboratory service by investigating: turnaround times, users opinions of the current service and potential alternative analytical methods.
Methods: An audit of the current analytical provision was used to assess its effectiveness and in order to elucidate the service users’ perception. This was effected by a questionnaire that was distributed to service users across three different NHS Trusts in England and Wales.
In an attempt to improve the laboratory service, alternatives to scanning spectrophotometry were investigated. These were selected through consideration of the nature of SAH i.e. blood is released into the subarachnoid space and the brain is damaged. Laboratory analysis therefore needed to focus on detecting the presence of blood and/or its breakdown products, any change in CSF constituents that arise as a direct consequence of blood being introduced in to the subarachnoid space or a specific analyte which would only be present if brain damage occurred. Investigation of current research into subarachnoid haemorrhage identified the following analytes as potential alternatives: CSF diazo bilirubin, CSF Ferritin, CSF protein S100 and serum protein S100.
Results: The audit revealed the average turnaround time for reporting xanthochromia results to be 26 hours, with almost 20% of samples being reported as equivocal. The service user’s questionnaire revealed a general lack of awareness of current United Kingdom National External Quality Assurance Scheme (UKNEQAS) guidelines for the ‘Analysis of cerebrospinal fluid for bilirubin in suspected Subarachnoid haemorrhage’ and a lack of understanding regarding the timing of lumbar punctures. Additionally, one third of users felt that the turnaround time for results was inadequate.
CSF protein S100 was found to be unsuitable due to the difficulty in achieving a suitable balance between sensitivity and specificity; at a cut-off of 0.40 μg/l sensitivity is 80% and specificity is 4%, at a cut-off of 1.60 μg/l sensitivity is 40% and specificity is 94%. Serum protein S100 was found to be unsuitable due to the difficulty in achieving a suitable balance between sensitivity and specificity at appropriate cut-offs (66 % and 73%, respectively, at a cut-off of 0.09 μg/l). When the CSF diazo bilirubin and CSF ferritin were compared to current laboratory practises using pre-defined criteria then CSF diazo bilirubin was found to be the analyte of choice to base new guidelines upon. CSF diazo bilirubin was then used as an initial ‘rule-out’ step in a new set of guidelines for the determination of SAH utilising CSF analysis.
Conclusion: The new guidelines employ CSF diazo bilirubin analysis as a ‘rule-out’ step with all samples that are above the cut-off (300 nmol/l) being processed through the UKNEQAS guidelines. In order for the guidelines to be introduced and accepted, local training and education programmes for laboratory and clinical staff will need to be developed and implemented and they will need to be disseminated through publication of articles in journals relevant to both the clinical biochemistry community and requesting clinicians.
|Date of Award||May 2013|
|Supervisor||Graham Mills (Supervisor)|