Prospective validation of cerebrospinal fluid bilirubin in suspected subarachnoid haemorrhage

Detection of subarachnoid haemorrhage with spectrophotometry of cerebrospinal fluid - a comparison of two methods

OBJECTIVES

Spectrophotometric absorption curve analysis of cerebrospinal fluid (CSF) for oxyhaemoglobin and bilirubin is necessary to accurately diagnose subarachnoid haemorrhage (SAH) in patients with typical symptoms but with negative findings on X-ray examinations. In this study, we evaluated the performance of two methods for interpreting absorption curves; one method from the United Kingdom National External Quality Assessment Service (UK-NEQAS) and the other from the national quality assurance programme in Sweden (Equalis).

METHODS

Consecutive absorbance curves (n=336) were interpreted with two different methods, and their performance was compared to the diagnosis as stated in the patient records.

RESULTS

The UK-NEQAS method displayed equal sensitivity to the Equalis method, but the specificity of the UK-NEQAS method was significantly higher than the Equalis method resulting in fewer false positive results. For UK-NEQAS, a positive predictive value (PPV) of 84.6% and a negative predictive value (NPV) of 99.7% were observed, whereas the Equalis method had a PPV of 27.5% and an NPV of 99.7%.

CONCLUSIONS

The semi-automated method based on the guidelines from UK-NEQAS provides an efficient and correct interpretation of absorbance curves with short turn-around times. We propose using this method for the routine interpretation of CSF spectrophotometric curves.

Uninterpretable cerebrospinal fluid absorbance scans caused by antibiotic therapy

BACKGROUND

The revised national guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage (UK) provide an objective means of assessing cerebrospinal fluid samples to determine the risk of subarachnoid haemorrhage. The guidelines are intended for general use, but samples rendered uninterpretable due to the presence of the antibiotic doxycycline have been described. Here, further cases of antibiotic-based interference, and their implications, are presented.

METHODS

An archival search of cerebrospinal fluid spectra performed at Hallands County Hospital Halmstad was performed for the years 2011 and 2016-2019 in an attempt to locate instances of interference. Each case of suspected interference was further investigated with in vitro reproduction experiments as a means of confirmation and assessment of potential clinical impact.

RESULTS

A total of 10 cases of cerebrospinal fluid curve interference were discovered: six due to doxycycline, three due to metronidazole and one due to tetracycline. Interference caused by the tetracycline class was revealed through in vitro experimentation to cause an apparent decrease in the sample's net bilirubin absorbance; the presence of xanthochromia on visual inspection was, however, conserved.

CONCLUSIONS

The problem of cerebrospinal fluid absorbance curve interference might be more common than previously suspected. Due to the potential net bilirubin absorbance-lowering effect of tetracyclines, the author recommends visual examination of cerebrospinal fluid samples in every case.

Analysis of blood degradation products and ferritin in the cerebrospinal fluid of dogs with acute thoracolumbar intervertebral disk extrusion, a prospective pilot study

Background

Hemorrhage in the spinal canal leads to further damage of the spinal cord influencing outcome in dogs with intervertebral disk (IVD) extrusion. The aim of the study was to evaluate blood degradation products and ferritin in the cerebrospinal fluid (CSF) of dogs with thoracolumbar IVD extrusion, and their association to clinical parameters and MRI findings.

Results

In the CSF of dogs with IVD extrusion, both net oxyhemoglobin absorption (NOA) and net bilirubin absorption (NBA) were significantly higher compared to the control groups of dogs with steroid responsive meningitis arteritis (SRMA) and idiopathic epilepsy (IE) (P < 0.001), but NOA compared to the idiopathic epilepsy group contaminated artificially with blood (IEc) was not (P = 0.890). Ferritin concentration was significantly higher in dogs with IVD extrusion compared to dogs with IE (P = 0.034), but not to dogs with SRMA (P = 0.526). There was no association between NOA, NBA or ferritin concentration and severity or duration of clinical signs. In dogs with a higher ferritin concentration the outcome was better (P = 0.018). In dogs with evidence of hemorrhage on MRI, NOA and NBA were significantly higher (P = 0.016, P = 0.009), but not ferritin (P = 0.0628).

Conclusion and clinical importance

Quantification of blood degradation products and ferritin in the CSF of dogs to assess subarachnoidal hemorrhage is feasible; however, larger case numbers are needed to evaluate the relevance of NBA and ferritin as prognostic indicators.

Update on the management of subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease. Outcome after SAH is mainly determined by the initial severity of the hemorrhage. Neuroimaging, in particular computed tomography, and aneurysm repair techniques, such as coiling and clipping, as well as neurocritical care management, have improved during the last few years. The management of a patient with SAH should have an interdisciplinary approach with case discussions between the neurointensivist, interventionalist and the neurosurgeon. The patient should be treated in a specialized neurointensive care unit of a center with sufficient SAH case volume. Poor-grade patients can be observed for complications and delayed cerebral ischemia through continuous monitoring techniques in addition to transcranial Doppler ultrasonography such as continuous electroencephalography, brain tissue oxygenation, cerebral metabolism, cerebral blood flow and serial vascular imaging. Neurocritical care should focus on neuromonitoring for delayed cerebral ischemia, management of hydrocephalus, seizures and intracranial hypertension, as well as of medical complications such as hyperglycemia, fever and anemia.

Bioinformatic software for cerebrospinal fluid spectrophotometry in suspected subarachnoid haemorrhage

Background

Diagnosis of subarachnoid haemorrhage (SAH) is firstly based on imaging and secondly on spectrophotometry. Bilirubin may be detected in the cerebrospinal fluid (CSF) for up to two weeks after SAH. CSF pigment analysis is commonly performed according to the Chalmers manual technique but may be prone to operator error. We propose an online software solution, based on the United Kingdom National External Quality Assessment Service (UKNEQAS) recommendations, to support the interpretation of CSF pigment analysis.

Methods

Based on the manual Chalmers technique, we have developed a web application (in Personal Home Page language including JpGraph module and an Oracle database®) that enables the calculation of net oxyhaemoglobin absorbance and net bilirubin absorbance. It uses data from the CSF spectrophotometry, CSF and serum protein concentrations, and serum bilirubin concentration to provide an interpretation based on the NEQAS decision tree. The application was retrospectively validated using the spectra from 350 patients, previously analysed by the manual method.

Results

In total, 91.1% interpretations from spectra analysed with the web application were in accordance with the results obtained manually. The 8.9% discordant results were mostly related to an incorrect interpretation using the manual technique.

Conclusions

The software developed in our laboratory to interpret CSF pigment analysis results is a precise, robust and useful tool that allows reproducible conclusions to be drawn. This software is available through a web interface.

The UKNEQAS scheme for cerebrospinal fluid haem pigments: a paradigm for service improvement

We describe the programme of an established External Quality Assurance (EQA) provider and a Specialist Advisory Group (SAG) to develop a successful EQA scheme for cerebrospinal fluid (CSF) haem pigments as an example of a professionally led, unfunded initiative with the real potential to benefit patients.

Within three years, we had assured sample stability, stoichiometry, and published best practice guidelines, enabling both analytical results and interpretation to be assessed and reported with an educative summary of the desired responses. Misclassification scoring of analysis and interpretation was introduced. Following audit, guidelines were modified and republished. The outcomes were as follows: Participant numbers increased from 63 at inception to 150 10 years later; The percentage of participants using visual inspection, a poor practice indicator, decreased from 27% to less than 1%; In all, 94–100% of participants consistently detected minor increases in bilirubin over the last four years of the scheme; More than 93% of participants were able to interpret analytical results linked to straightforward clinical scenarios; Misclassification scoring demonstrated that more complex scenarios repeatedly posed problems and is the next challenge to address. Scheme success is attributed to the experience of the operator and the formation of a voluntary expert advisory group, with both concerned to advance science and patient safety and thus contribute unpaid time and effort in order to succeed. In times of fiscal constraint, such resource may not be so readily available, yet is a vital part of continuous quality improvement for the benefit of patients.

What is the role of cerebrospinal fluid ferritin in the diagnosis of subarachnoid haemorrhage in computed tomography-negative patients?

Background

Spectrophotometry of cerebrospinal fluid (CSF) for bilirubin is the recommended method for investigation in suspected cases of subarachnoid haemorrhage (SAH), when a computed tomography (CT) of the head is negative for blood. There is a potential need for a simpler alternative. Measurement of CSF ferritin might fulfil this need.

Method

We have measured ferritin in the CSF from 252 patients with suspected SAH who were negative on a CT of the head for blood, recruited on a consecutive intention to recruit basis from four centres. CSF spectrophotometry was performed on all samples. A positive outcome was taken as an aneurysm found on angiography that was treated or a discharge diagnosis of non-aneurysmal SAH.

Results

A final diagnosis of aneurysmal SAH was made in six patients, an arteriovenous malformation in one and non-aneurysmal SAH in nine. Receiver operating characteristic (ROC) analysis showed that at 6.4 μg/L, sensitivity, specificity, positive and negative predictive values were 1.0, 0.48, 0.12 and 1.0, respectively. At 12 μg/L, these values were 0.81, 0.91, 0.38 and 0.98, respectively.

Conclusions

At an appropriate negative predictive value (1.0) for a rule-out test, ferritin has too low a specificity to function as a stand-alone test and we cannot recommend it as an initial screen to be followed by spectrophotometry.