ACP Best Practice No 166: CSF spectrophotometry in the diagnosis of subarachnoid haemorrhage

Abstract

After subarachnoid haemorrhage (SAH), cerebral angiography is usually performed to establish a site of bleeding, which may then be treated surgically to prevent a potentially catastrophic re-bleed. The investigation of choice in the diagnosis of SAH is computerised tomography (CT). However, because CT can miss some patients with SAH, cerebrospinal fluid (CSF) spectrophotometry should be performed in those patients with negative or equivocal CT scans or those who have presented several days after the suspected bleed. Spectrophotometry should aim to detect the presence of both oxyhaemoglobin and bilirubin because either one or both of these pigments may contribute to xanthochromia following SAH. CSF supernatant is scanned using a double beam spectrophotometer at wavelengths between 350 nm and 650 nm. Oxyhaemoglobin alone produces an absorption peak at 413-415 nm, bilirubin alone produces a broad peak at 450-460 nm, and bilirubin together with oxyhaemoglobin produce a shoulder at 450-460 nm on the downslope of the oxyhaemoglobin peak. To minimise the frequency of false positive and false negative results, a protocol has been developed, which is described.

Cerebrospinal fluid analyses for the diagnosis of subarachnoid haemorrhage and experience from a Swedish study. What method is preferable when diagnosing a subarachnoid haemorrhage?

“…This process starts shortly (2-4 h) after the bleeding, and oxyhaemoglobin can be detected in CSF from approximately 2-12 h after ictus [34]. Oxyhaemoglobin, the oxygenated form of haemoglobin, has an absorbance maximum around 415 nm, in the violet region of the optical spectrum ( Figure 1A) [28].…”

Definitive angiographic detection of subarachnoid haemorrhage compared with laboratory assessment of intracranial bleed in CT-negative patients

“…11 However, guidelines produced under the auspices of the UK National External Quality Assurance Group (UKNEQAS) (which are currently available via http://www.immqas.org.u k/ csfguidelines.pdf) advocate that the key pigment to detect is bilirubin. The guidelines state that the presence of oxyhaemoglobin on its own has a low predictive value for SAH.…”

Pneumatic tube transport of blood-stained cerebrospinal fluid specimens has no clinically relevant effect on rates of haemolysis compared to manual transport

“…Other red blood cell breakdown products contributing to this discolouration are oxyhaemoglobin and methaemoglobin. 2 Methaemoglobin is uncommon and will not be considered further. 3 Although xanthochromia can be detected by visual inspection alone, this is considered inferior to spectrophotometry.…”

“…Red blood cells in CSF undergo lysis releasing oxyhaemoglobin within 2 to 12 h. 2,5 In vivo, oxyhaemoglobin is usually converted into bilirubin by the action of macrophages and other leptomeningeal cells. This process takes at least 6 h and up to 15 h to form post bleed.…”

“…This process takes at least 6 h and up to 15 h to form post bleed. 2,[5][6][7][8][9] Hence, current advice is to wait at least 6 h and preferably 12 h after the onset of headache before performing lumbar puncture to investigate suspected SAH. 8 Mechanical haemolysis of red blood cells in collected CSF specimens may also release oxyhaemoglobin but bilirubin is not produced due to the absence of in vivo enzyme systems.…”