A Normative Model of Serum Inhibin B in Young Males

Abstract

Inhibin B has been identified as a potential marker of Sertoli cell function in males. The aim of this study is to produce a normative model of serum inhibin B in males from birth to seventeen years. We used a well-defined search strategy to identify studies containing data that can contribute to a larger approximation of the healthy population. We combined data from four published studies (n = 709) and derived an internally validated model with high goodness-of-fit and normally distributed residuals. Our results show that inhibin B increases following birth to a post-natal peak of 270 pg/mL (IQR 210-335 pg/mL) and then decreases during childhood followed by a rise at around 8 years, peaking at a mean 305 pg/mL (IQR 240-445 pg/mL) at around age 17. Following this peak there is a slow decline to the standard mature adult normal range of 170 pg/mL (IQR 125-215 pg/mL). This normative model suggests that 35% of the variation in Inhibin B levels in young males is due to age alone, provides an age-specific reference range for inhibin B in the young healthy male population, and will be a powerful tool in evaluating the potential of inhibin B as a marker of Sertoli cell function in pre-pubertal boys.

Fig 1. Root transformed Inhibin B levels.

The red line is the model that best fits the 709 data points, which are indicated by blue squares. The model has r² = 0.35, indicating that 35% of the variation in inhibin B levels in young males is due to age alone. The green lines represent the upper and lower 95% confidence limits for the predicted mean and the orange lines the upper and lower 95% prediction limits.

Fig 2. Model residuals.

The residuals are the variations in root-adjusted observed values from the root-adjusted age-related mean value predicted by the model. The residuals have 97% goodness of fit to an ideal Gaussian curve.

Fig 3. The Normative Model.

Inhibin B levels in human males from birth to age 17 years expressed as standard centiles.