Assessing hypogonadism in men--how helpful are current testosterone assays?

In recent years, hormone therapy (HT) with testosterone has gained increasing prominence and popularity in aging men. It has a demonstrated ability to decrease fat mass and increase lean body mass in men with initial 'low' testosterone levels. The Australian Pharmaceutical Benefits Scheme (PBS) only allows subsidisation of male HT if two morning testosterone values are <8.0 nmol/L (or 8-15 nmol/L with elevated luteinising hormone [LH]). The scientific basis of this 'cut off' for testosterone replacement is unclear but it is close to the lower limit of normal for some laboratories. There is well documented diurnal variation (and even seasonal variation) of testosterone. However, the PBS requirements avoid such diurnal variation by requiring two morning blood samples. The underlying assumption is that all laboratories obtain similar results.