Hormones
Insulin: Insulin is secreted by the pancreas in response to eating or elevated blood sugar. It is deficient in persons with type 1 diabetes, and present at insufficient levels in persons with type 2 diabetes. The natural evolution of type 2 diabetes causes insulin levels to fall from high levels to low levels over a course of years. Thus insulin levels in persons with type 1 and type 2 diabetes overlap significantly, and insulin levels are not very useful in determining type 1 vs type 2. Insulin levels vary widely from person to person depending upon an individual’s insulin sensitivity (or conversely, their insulin resistance.) Insulin levels also vary widely according to when the last meal occurred. Insulin resistance is a risk factor for coronary disease, thus assessing an individual's insulin resistance may have some value using the HOMA-IR calculation. Insulin levels are also elevated in patients with true hypoglycemia; however the interpretation of these levels is difficult. Insulin levels, when measured alone at a random time, is rarely useful.
C-peptide: This is a fragment cleaved off of the precursor of insulin (pro-insulin) when insulin is manufactured in the pancreas. C-peptide levels usually correlate with the insulin levels, except when people take insulin injections. When a patient is hypoglycemic, this test may be useful to determine whether high insulin levels are due to excessive pancreatic release of insulin, or from an injection of insulin.
Estradiol: This is the most commonly measured type of estrogen measured. In women it varies according to their age, and whether they are having normal menstrual cycles. Hormone levels are also changed when taking birth control pills or estrogen replacement.
Testosterone: This is the male sex hormone, however both men and women have detectable testosterone levels. In men the major source is the testicles, in women the ovaries. Like thyroid hormone, this hormone is also carried by proteins, such as Sex Hormone Binding Globulin (SHBG). The amount of binding proteins can vary from person to person, or depend on other medical conditions, thus skewing the results of the Total Testosterone. A 'Free Testosterone' reduces this possible interference. In men, low levels of testosterone can indicate reduced testicular function, or 'male hypogonadism.' This can be due to disease, aging, or damage to the testicles, 'testicular or primary hypogonadism.' It may also be due to inadequate function of the pituitary gland or hypothalamus 'secondary hypogonadism' from diseases that affect the pituitary. High testosterone can occur from testosterone injections, testosterone receptor defects, or testosterone secreting tumors.
In women, high testosterone levels can occur because of production from either the ovaries or adrenal glands. Adrenal hormones such as DHEA can be converted in to testosterone.
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