Whilst copeptin is very robust for measurement ex vivo, it behaves in a similar way to AVP in the circulation, and the two markers are closely correlated.Ref-4 Copeptin concentrations in healthy volunteers range between 1 and 12 pmol/L (upper 97.5 percentile) with median values < 5 pmol/L.Ref-4, Ref-20 Men consistently show slightly higher values compared with women, but the difference in median values is only about 1 pmol/L.Ref-4, Ref-20 In contrast to many other biomarkers, the copeptin plasma concentration was similar in different age groups and showed no correlation with age.Ref-4

Copeptin responds to changes in plasma osmolality with a kinetic increase/decrease similar to that reported for AVP.Ref-4, Ref-21 Patients with diabetes insipidus and reduced AVP have very low plasma levels of copeptin,Ref-22 whilst patients with hyponatremia and the syndrome of inappropriate ADH secretion (SIADH) have elevated copeptin in their circulation.Ref-23

Whilst the normal range of copeptin mirrors the physiological AVP secretion needed to maintain plasma osmolality, in severe diseases or states, such as shock, sepsis, stroke, or cardiovascular diseases, the nonosmotic release of AVP is depicted by a sharp increase in plasma copeptin, which has diagnostic and prognostic value.


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