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Friday, July 20, 2012

Testosterone Blood Tests Should Be Done in a Fasted State

Thanks to Dr Scally for this reference ( )

Serum Testosterone Decrease After A Mixed Meal Independent Of SHBG And Gonadotrophins

The secretion and concentration of plasma sex steroids can be affected by both genetic and environmental factors. Testosterone levels have a circadian rhythm with the highest circulating levels during the morning. Sampling for S-T determination is recommended to take place in morning hours between 07 and 11.00 h after a normal night’s sleep to have a truly representative assessment and avoid false low concentrations.

Most clinical protocols have no food intake restrictions prior to blood sampling for S-T assessment. However, earlier reported human studies have indicated an effect of food intake on serum testosterone levels, suggesting that food intake may influence the diurnal rhythm. On the other hand, previous studies have also shown that mixed carbohydrate and protein meal has no effect on total or free testosterone concentrations while acute fat intake decreases S-testosterone level and chronic high fat intake increases S-testosterone level. It has been hypothesized that acute fat intake increases the level of chylomicrons, which can reduce LH-stimulated testosterone production in vitro. However, these findings were not confirmed in vivo in a study that changed dietary fat intake from 37% to 64%.

Hence, several factors may be expected to affect the circadian rhythm of testosterone level and the impact of diet on serum testosterone level needs further investigation. Clinical evaluation of male gonadal activity often requires investigation of the hypothalamus-pituitary-testis axis. Accurate biochemical determinations are crucial to identify and exclude confounding factors that influence testosterone level. Therefore, researchers undertook a strictly controlled crossover study to investigate the effect of fed state compared to fasting state on S-T, S-LH and S-SHBG serum levels during the morning in healthy men.

In summary, their study verifies that food intake decreases testosterone level in serum in healthy men, with a 30% reduction in testosterone compared to the fasting condition. They recommend that the serum testosterone should be measured in starving condition in the morning to reduce the risk of inaccurate low testosterone levels in the investigation of men where there is clinical suspicion of hypogonadism.

Lehtihet M, Arver S, Bartuseviciene I, Pousette Å. S-testosterone decrease after a mixed meal in healthy men independent of SHBG and gonadotrophin levels. Andrologia

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