Assay for the Measurement of Copeptin, a Stable Peptide Derived from the Precursor of Vasopressin

Arginine vasopressin (AVP) is a key regulator of water balance, but its instability makes reliable measurement difficult and precludes routine use. We present a method for quantifying AVP release by use of copeptin, a glycopeptide comprising the C-terminal part of the AVP prohormone. We measured copeptin in 50-microL serum and plasma samples from healthy individuals and from critically ill patients with sepsis. Our sandwich immunoluminometric assay used 2 polyclonal antibodies to amino acids 132-164 of pre-provasopressin. The assay yielded results within 3 h. The analytical detection limit was 1.7 pmol/L, and the interlaboratory CV was 2.25 pmol/L. The assay was linear on dilution of the analyte. Ex vivo copeptin stability (