Abstract
Corticotropin is notorious for its instability. Whereas several studies have investigated its short-term stability in plasma following venous blood sampling, studies on long-term stability are lacking. Here we investigated the long-term storage stability of corticotropin in ethylenediaminetetraacetic acid containing plasma. Specimens from healthy volunteers (neat, spiked) were stored in polypropylene microcentrifuge tubes with socket screw-caps at-20°C and-70°C for up to one and a half years. Corticotropin in plasma was measured using an Abbott research only immunoassay. Separately, specimens from patients were collected during diagnostic routine testing and stored in polystyrene tubes with push-caps at-20°C for up to 6 years. In these samples corticotropin hormone was measured using the Diasorin corticotropin immunoassay. Storage of specimens at-20°C or-70°C for up to one and a half years showed minimal changes (<11%) in corticotropin levels, while storage of patient samples at-20°C for up to 6 years showed a significant (54%) reduction in corticotropin levels. Corticotropin levels are stable in plasma when stored at-20°C for one and a half years using the Abbott research only assay, but with longer storage time a significant reduction in corticotropin levels can be expected. Once specimens are stored for future corticotropin measurements, one should consider storage time, storage temperature and assay differences.
Highlights
Corticotropin is a 39-residue polypeptide tropic hormone secreted by the anterior pituitary gland following hypothalamic corticotropinreleasing hormone release
Corticotropin levels are stable in plasma when stored at −20 °C for one and a half years using the Abbott research only assay, but with longer storage time a significant reduction in corticotropin levels can be expected
Experiment 1: Storing human plasma specimens for up to one and a half years at −20 °C or −70 °C had limited influence on the adrenocorticotropic hormone (ACTH) levels in these specimens measured by the ARCHITECT ACTH assay
Summary
Corticotropin (adrenocorticotropic hormone, ACTH) is a 39-residue polypeptide tropic hormone secreted by the anterior pituitary gland following hypothalamic corticotropinreleasing hormone release. ACTH is cleaved from precursor hormone pro-opiomelanocortin, and plays an important role in the hypothalamic–pituitary–adrenal axis by stimulating the production and secretion of cortisol from the adrenal cortex. Measurements of plasma ACTH are crucial for differential diagnosis of endocrine disorders including Cushing’s syndrome and adrenal insufficiency but can be complicated by both preanalytical and analytical factors. For long-term storage, it is generally advised to store specimens at −70 °C. This may, not always be possible in daily practice (for clinical diagnostics or research) because of limited −70 °C freezer space. The longer the storage time, the higher the chance of degradation of unstable analytes [9].
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