hormone clearance

Hormone clearance is how fast the body removes a hormone from the blood, by breaking it down or excreting it. If secretion is the faucet filling the sink, clearance is the drain emptying it — and the steady level in the blood depends on both. A hormone whose secretion stops will only fade as quickly as clearance allows.

The two main routes are metabolism, mostly in the liver and kidney, where enzymes chemically dismantle the hormone, and excretion, where the hormone or its breakdown products leave in urine or bile. Water-soluble peptide and amine hormones are cleared quickly and have short half-lives measured in minutes; fat-soluble steroids and thyroid hormones, shielded by carrier proteins, are cleared slowly and can linger for hours to days.

Clearance shapes how a hormone is used and dosed. Because catecholamines clear in seconds, the body can switch them off almost instantly; because thyroxine clears over about a week, it can be taken as a once-daily pill. Liver or kidney disease slows clearance and can let hormones accumulate, while some medications speed it up by inducing metabolizing enzymes.