Correspondence

Adrenocorticotrophin (ACTH) is formed from the cleavage of pro-opiomelanocortin. Measurement of plasma ACTH is a key step in the differential diagnosis of hypothalamic-pituitary-adrenal disorders. Prior to the development of radioimmunoassay, the bioassays employed for the determination of ACTH were highly complex, time-consuming and costly in terms of number of animals used. Their sensitivity was such that the normal early morning peak of ACTH could not be determined. The introduction of immunoassay methodology enabled the measurement of low normal ACTH concentrations. Immunological recognition of ACTH by the antibodies employed offered improvements with regard to speci city. The development of two-site immunometric assays further improved speci city and the ability to measure low normal ACTH concentrations without the need to extract large volumes of plasma. The quanti cation of ACTH is now routinely performed in clinical laboratories, with non-radioisotopic methods becoming increasingly popular