http://www.ncbi.nlm.nih.gov/m/pubmed/14719513 :

Abstract

BACKGROUND: This report describes the sensitivity and specificity of glucose detection using Glucostix test strips and computed tomography (CT) of the skull base for confirming cerebrospinal fluid (CSF) fistulae in patients with persistent rhinorrhoea or otorrhoea, and comparing them with the beta-2 transferrin assay as the gold standard for CSF detection.

METHODS: Fluid samples from the nose were collected from 18 patients with suspected CSF fistulae. The samples were assayed for beta-2 transferrin using the Western blotting and immunostaining technique. CT (5mm axial slice) of the skull base was performed for evidence of skull base fracture. The glucose levels and Glucostix results were compared.

RESULTS: Out of the 18 samples, 15 were positive for beta-2 transferrin and the leaks were validated surgically in 10 patients. Give leaks healed spontaneously with conservative management. Glucostix tests produced three false positive results from blood and nasal mucus contaminated fluid. Glucostix failed to detect another three CSF leaks resulting from false negative tests because of low CSF glucose levels. The Glucostix glucose test was nonspecific and insensitive compared with the beta-2 transferrin assay. CT failed to detect three of the 15 beta-2 transferrin-positive leaks but there were no false positive results. CT produced six negative results, of which three were false negatives.

CONCLUSIONS: Glucose detection using Glucostix test strips is not recommended as a confirmatory test due to its lack of specificity and sensitivity. In the presence of a skull bas fracture on CT and a clinical CSF leak, there is no need for a further confirmatory test. In cases where a confirmatory test is needed, the beta-2 transferrin assay is the test of choice because of its high sensitivity and specificity.

New insights into the glucose oxidase stick test for cerebrospinal fluid rhinorrhoea:

Abstract

Rhinorrhoea is a clinical sign of cerebrospinal fluid (CSF) leakage in patients with skull fracture, but can also be attributable to respiratory secretions or tears. Laboratory tests confirming the presence of CSF are not sufficiently rapid to support clinical decision making in the emergency department and may not be universally available.

Detection of glucose in nasal discharge was traditionally used to diagnose CSF leak at the bedside, but has fallen into disuse as it has poor positive predictive value. We propose an algorithm to improve the diagnostic value of this test taking into consideration factors we have found to affect the glucose concentration of respiratory secretions. In patients at risk of CSF leak, nasal discharge is likely to contain CSF if glucose is present in the absence of visible blood, if blood glucose is <6 mmol.L−1, and if there are no symptoms of upper respiratory tract infection.

Cerebrospinal fluid (CSF) leakage from dural tears complicates around 20% of basilar skull fractures and 25% of facial fractures.1,2 As CSF leakage is commonly complicated by intracranial infection in 3–31% cases,1,3,4 it is important not to miss the diagnosis. Clinical suspicion of CSF leak should be raised by the presence of rhinorrhoea; however, differentiating CSF from other causes of nasal discharge (respiratory secretions, tears, and blood) presents a diagnostic challenge. Immunofixation electrophoresis of nasal secretions in the laboratory can be used to detect β-2-transferrin—a protein produced by neuraminidase activity in the brain and uniquely found in CSF and perilymph.5 This test is not sufficiently rapid to provide support for clinical decision making in emergency departments and may not be available in all hospitals, particularly in developing countries.

Measurement of the glucose concentration of nasal discharge is a traditional bedside test for the detection of CSF leaks. Glucose oxidase sticks are wetted with nasal secretions and colour change is compared with a calibrated scale to determine glucose concentration. The presence of glucose is taken to indicate that secretions contain CSF. This test is easy to perform, cheap, and widely available, but has poor positive predictive value for CSF leakage. Glucose was detected in nasal discharge from 15/17 normal children6 and in 44% of clear nasal and lacrimal secretions from people without any risk factor for CSF leak.7 False negative results, where glucose oxidase sticks have failed to detect CSF, have also been reported.5,8 We propose that if factors determining the appearance of glucose in respiratory secretions can be explained, this old test could still have a role in identification of CSF leaks.

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