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Inhibin B in Plasma Samples from Male Volunteer Panel Selected for Health but Not Fertility: Sources of Variability


Correspondence to: Jane Stewart, Global Safety Assessment, AstraZeneca Pharmaceuticals. Alderley Park, Macclesfield, Cheshire UK, SK10 4TG. E-mail:



Inhibin B was measured in plasma samples obtained from 34 healthy male subjects selected on criteria typical for a phase I clinical trial across a wide age range (19–70 years).


Mutiple samples (up to seven per subject) were obtained as a set consisting of one baseline sample then three pairs of morning and evening samples. This allowed assessment of the fed/fasted state and diurnal effects. Samples were analyzed using a commercially available inhibin B ELISA assay. Across all time points, the mean plasma inhibin B was 197 pg/ml ± 67pg/ml.


The results confirmed a diurnal effect where inhibin B concentration is on average about 40 pg/ml greater in the morning and showed a negative influence of age on inhibin B concentrations. There was no overt influence of body mass index on inhibin B. A variance components analysis revealed that more than 80% of the total variability was due to the variability observed between individuals. Within the fed-fasted sampling schedule of this study, inhibin B levels were slightly lower when volunteers had eaten but the magnitude of this effect was within the variance encountered between occasions.


These results illustrate that when undertaking longitudinal monitoring of inhibin B in clinical trials as means of monitoring testicular function, it is important to obtain samples from an individual at the same time of day and to use statistical methods which analyze the magnitude of deviation of an individual from their personal baseline as well as looking at group means and influence of study duration.