Can a 15-Hour (Overnight) Urinary Catecholamine Measure Substitute for a 24-Hour Measure?

This study examined whether 15-hr and 24-hr urinary catecholamine measures show comparable associations with other physiological measures that are expected to correlate with sympathetic nervous system activity. Participants (193 healthy adults) provided 24- hr urine samples that were collected in a controlled environment (hotel), and divided into 9-hr daytime and 15-hr overnight collections. On the same day, resting blood pressure (BP) was measured, and 8 samples of salivary cortisol were collected. Catecholamine (15-hr and 24-hr) measures were correlated substantially in the entire sample, and when examined separately by sex and by race. Both 15-hr and 24-hr epinephrine (E) correlated significantly with systolic BP and cortisol; 15-hr and 24-hr norepinephrine (NE) corre- lated significantly with cortisol. Correlation coeficients for 15-hr measures were similar, but not equivalent to those for 24-hr measures. Urinary catecholamines obtained via 15- hr overnight collection approximated but were not equivalent to catecholamines obtained via 24-hr collection. Overnight collection was associated with reduced power to detect significant associations of catecholamines with criterion variables, such that use of 15-hr rather than 24-hr sampling required a relative increase in sample size of 1.32 times for E and 1.18 times for NE to detect similar effects. Researchers should weigh the costs of additional subjects to the benefit of decreased burden when choosing between the two sampling methods.