Hormone Pulsatility Discrimination Via Coarse and Short Time Sampling

Pulsatile hormonal secretion is a ubiquitous finding in endocrinology. However, typical protocols employed to generate data sets suitable for "pulsatility analysis" have required 60-300 samples, rendering such studies largely research methodologies, due primarily to considerable assay expense. One successful mathematical strategy in calibrating changes in pulsatility modalities is approximate entropy (ApEn), a quantification of sequential irregularity. Given the degree of differences between ApEn values in pathophysiological subjects vs. healthy controls reported in several recent studies, we queried to what extent coarser (less frequent) and shorter duration time sampling would still retain significant ApEn differences between clinically distinct cohorts. Accordingly, we reanalyzed data from two studies of 24-h profiles of healthy vs. tumoral hormone secretion: 1) growth hormone comparisons of normal subjects vs. acromegalics, originally sampled every 5 min; and 2) ACTH and cortisol comparisons of normal subjects vs. Cushing's disease patients, originally sampled every 10 min. By multiple statistical analyses, we consistently and highly significantly (P < 0.0001) established that serum concentration patterns in tumor patients are more irregular than those of controls, with high sensitivity and specificity, even at very coarse (e.g., 60 min) sampling regimens and over relatively short (2-4 h) time intervals. The consistency of these findings suggests a broadly based utility of such shorter and/or coarser sampling methodologies. Substantial reduction in sampling requirements holds the potential to move analysis of pulsatile hormone release from a primarily research tool to a clinically applicable protocol, in appropriate diagnostic and therapeutic contexts.