Introduction
This topic covers how hormones are measured in serum, plasma, urine and other body fluids: the main chemical classes and what they mean for testing, the choice and handling of biological material, the preparation the patient needs, the indications for testing, and how results are read against reference intervals and clinical context. It is the methodological basis for the endocrine topics that follow, so a good answer shows that hormone results are only meaningful when the sample, the timing and the patient's state are known.
Basic groups of hormones and why they matter for testing
Hormones are grouped by chemical structure. The structure determines solubility, transport in blood, half-life, the stability of the sample and the type of assay used.
The key practical point is that most circulating hormone is protein-bound, while only the free fraction is biologically active. Total concentration therefore changes when binding proteins change, for example with pregnancy, oral contraceptives, liver disease or nephrotic syndrome, even when the free hormone is normal.