Endocrine system includes different endocrine glands that secrete completely different hormones/molecules. Some of them are interdependent, however, measurements of different hormone levels are taken by specific laboratory tests for that particular hormone secreted by specific endocrine gland.
I shall provide you with the example of Thyroid gland, in contrast to other endocrine organs that have limited storage capacity, this gland is different. It produces thyroid hormones depending on the follicular storage of the prohormone thyroglobulin.
Thyroid hormone production and secretion includes exocrine and endocrine phases that are regulated by TSH (thyroid stimulating hormone).
There are various specific steps of hormone production and secretion that may be affected by dietary as well as genetic factors.
Dietary iodide deficiency causes hypothyroidism.
Sometimes thyroid gland is overactive and the condition is called hyperthyroidism.
Usually, thyroid malfunction leads to clinical symptoms that may be milder to extreme. A physician recognizes those symptoms and orders a test to measure thyroid hormone level.
Hope this helps.