Chapter 2.5 - Normal concentrations of steroids and their regulators in blood

Abstract

The concentrations of steroids in serum or plasma of blood in the basal state is the starting point for nearly all laboratory investigations of related clinical problems. The concentrations of steroids in blood plasma represents the level of exposure of tissues at a particular moment in time and the results of the tests need to consider the exact time (hours in the day) and other temporal measures (age, sexual development, and time in menstrual cycle) when the sample was taken. The steroids in serum are largely bound to proteins so only a small amount of steroids hit the target receptors. Unlike thyroid investigations where free hormones are measured this has not yet become common practice with steroids. The measurements of free steroid concentrations are improving so there may be a change in future. The results of analytical tests require judgment based on many factors. In the case of aldosterone, measurements of the electrolyte status will have been determined. The laboratory and clinician need to work together to optimize interpretation of the results. Venous blood in general should be taken directly into a syringe although sometimes blood taken via a catheter is needed to examine for instance the concentration of steroids draining an organ. The control of steroid secretion has to be considered during development and reproductive function and body homeostasis by measurements of the regulatory peptide hormones. Some new proteins that influence the gonadal axis are now included. Establishing reference intervals for the results requires careful selection of subjects for samples and is particularly difficult in pediatrics. Separation of results by age is effective for some steroids but not the sex steroids where pubertal staging needs to be taken into account.