Urinary excretion of 5-hydroxyindoleacetic acid--no relationship to the level in cerebrospinal fluid

Concentrations of 5-hydroxyindoleacetic acid (5-HIAA) were determined in urine and cerebrospinal fluid (CSF) by mass fragmentography. A pronounced day-to-day variation in the urinary excretion of 5-HIAA was found both in psychiatric patients and a healthy control. Lumbar punctures performed twice 3-12 weeks apart in 11 healthy controls resulted in reproducible levels of 5-HIAA in CSF (r = 0.89; P less than 0.001). The mean of three periods of daily 5-HIAA excretion was not correlated to the CSF level measured in 18 psychiatric patients (r = 0.09). Three weeks of chlorimipramine treatment significantly decreased CSF 5-HIAA levels (P less than 0.05), but not the urinary excretion of 5-HIAA. It might be concluded that measurement of urinary 5-HIAA excretion is of little value compared to CSF levels in studies of serotonin in the central nervous system.