Obtaining information from the brain in a non-invasive way: determination of iron in nasal exudate to differentiate hemorrhagic and ischemic strokes

Background: Differentiation between hemorrhagic and ischemic stroke is currently made by brain imaging or analyzing blood and cerebrospinal fluid (CSF) samples. After describing a new drainage route from brain to nasal mucosa, nasal exudate samples can be considered a new and promising source of biomarkers. Saliva can also be evaluated. Methods: We determined iron in nasal exudate and saliva samples from patients of acute stroke during the first 48 h from onset. A simple, non-invasive sampling procedure was employed to obtain information from the brain. Samples were taken with a pre-weighed swab, solved in a 2% nitric acid solution and iron was measured by inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS). Results: A significant difference in the dispersion of results of iron concentration for both stroke subtypes was observed in nasal exudate samples. The interquartile range was 0.608 nmol mg(-1) of iron for hemorrhagic strokes and only 0.044 nmol mg(-1) for ischemic strokes. In saliva samples, however, the values were 0.236 vs. 0.157 nmol mg(-1). A cut-off limit of 0.102 nmol of iron per mg of nasal exudate provides a methodology with a 90% of sensitivity and a 90% of specificity. The value of the area under (AUC) the receiver operating characteristic curve (ROC) for nasal exudate samples is 0.960, considered as very good in which regards to its predictive value. Conclusions: Non-invasive samples of nasal secretion have allowed obtaining, for the first time, information from the brain. Determination of iron in nasal exudate by ICP-MS allowed differentiation between ischemic and hemorrhagic strokes.