Test Details: Angiotensin Converting Enzyme (ACE) is a main component of renin- angiotensin system. ACE converts the hormone angiotensin I to the active vasoconstrictor angiotensin II, causing the constriction of blood vessels and thereby increasing the blood pressure. Increased ACE concentrations in CSF are associated with neurosarcoidosis, neurologic diseases such as bacterial and viral meningitis and Behcet disease. Decreased concentrations have been reported in patients with Alzheimer disease, Parkinson disease, and progressive supranuclear palsy.