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Hyponatremia after traumatic brain injury (TBI) may influence neurological function and treatment. A causal relationship between elevated serum concentrations of Type B natriuretic peptide (BNP) and hyponatremia has been implied after subarachnoid hemorrhage and other neurosurgical disorders, although the source of BNP has not been identified. We evaluated if hyponatremia and increased BNP occur after TBI and if BNP is produced/released by the brain within 24 h after injury.NT-proBNP was measured in concomitant jugular venous and arterial blood samples within 24 h after TBI. NT-proBNP was elevated in both samples in six patients (24%). One patient (4%) showed an increased jugular NT-proBNP concentration above a normal arterial concentration, suggesting a brain source. In the other 24 patients the difference between jugular and arterial NT-proBNP was not statistically significant. Hyponatremia (or =136 mEq/l) also occurred in six patients (24%), but only two (8%) had both increased arterial NT-proBNP and hyponatremia. In both the urine sodium was slightly elevated above normal, but not statistically different from other patients. The difference in serum sodium between hypo- and normo-natremic groups was significant, but mean NT-proBNP and jugular:arterial NT-proBNP differences were not.In this pilot study BNP is elevated within 24 h after TBI in some patients. However, it does not originate from the brain and increased NT-proBNP concentrations are not consistently associated with hyponatremia or increased urinary sodium loss. more...