Is serum copeptin a modifiable biomarker in autosomal dominant polycystic kidney disease?

Table 1 Distinct production sites of precursor arginine vasopressin in hypothalamus

Site of synthesis in hypothalamus	Magnocellular neurons (Supra-optic and paraventricular)	Parvocellular neurons
Processing of AVP	Occurs during axonal transport in the infundibulum with copeptin and neurophysin acting as chaperones for correct AVP folding	Occurs in the parvocellular neurons where it released with other releasing hormones, such corticotrophin releasing hormone
Storage	Posterior pituitary	Hypothalamus
Stimuli for release	Osmotic and haemodynamic stimuli from the posterior pituitary gland	Released in response to humoural stress together with CRH, which both act on the adrenal gland to release cortisol

AVP: Arginine vasopressin.

Table 2 Summary of vasopressin limitations compared to copeptin advantages as a biomarker using the thermo scientific B.R.A.H.M.S KRYPTOR assay (adapted from Thermo Fisher scientific)

Features	Limitations of measuring AVP	Advantages of CT-proAVP (Copeptin)
Ex vivo stability	Unstable (even at -20 °C)	Stable at > 3 d at room temperature
Sample volume required	400 L	50 μL
Time to results	3 working days	approximately 1 h
Sensitivity	Low (small molecule size, measured only by competitive immunoassay)	High (larger size, can be measured using a sensitive sandwich immunoassay)
Measuring range	1.15-73.8 pmol/L	0.7-500 pmol/L and up to 2000 pmol/L with automated dilution
Handling	Manual	Automatic

AVP: Arginine vasopressin.